AM Radio RFI - RDWRIOR, got yer ears on?

[The_Raven]

Howyadoin,

My '96 SLS has a problem with AM reception where the signal goes all static-y and such when I go over 5 MPH. Idle is fine, revving the engine in Park has no effect, a slow roll has no effect, but when I get over 5 MPH or so, whammo!

In a previous topic on the old board, someone else reported the same problem. It was recommended that he pulling the RSS fuse to determine if the problem was there. Where is this fuse in a '96 SLS? I looked in the owner's manual but couldn't locate it in the fuse block diagrams.

If killing RSS does prove to fix the problem, is there a way to determine which component is at fault? I'm going to replace the existing Delco base AM/FM/cassette with an aftermarket system, but there's no point in doing this until I resolve this RFI issue...

Thanks as always!

[RDWRIOR]

Raven,

The person (Richard K.) who originally brought up this topic on the old message board (a little over one year ago) enagaged in a "back and forth" dialogue via private e-mail, in which various possible root causes of the radio interference were discussed. The leveling and/or suspension control systems were eventually ruled out as the interference source, so removing the 'RSS' fuse will probably be a waste of your time. Ultimately, two possible root causes were considered, but they were never evaluated because the "incident" '96 Deville was traded in on a new '03 Deville. Late last year, another person (Michael C.) corresponded via private e-mail, inquiring about this same radio subject. Below is the relevant text from replies, which also serves as the best reply that I can give you at this time. To my knowledge, no one has tried either of the EGR or transmission circuit evaluations that are described. So, I really don't know if either is the source of the radio interference problem, and thus, I can't (yet) tell you what, if anything, can be done to eliminate the problem.

The following is text copied from the reply message to Michael C., dated 11/18/03:

Mike,

The caddyinfo.com post that you referenced was just the first of many private e-mail exchanges that I had with the other gentleman who requested assistance with the AM radio interference problem. He found that removing the 'RSS' fuse had no effect, nor did many other ideas that I asked him to try out. There were two other possible causes that I had advised him to check out, but before he had an opportunity to do so he decided to trade in his '97 Deville on a new '03 Deville. So, I do not have a definitive solution for the problem, but I can advise you of the remaining possibilities that were never explored before.

I reviewed my archived e-mail messages on this subject, and I have copied the following from one of my last exchanges with the other Deville owner:

Try disabling the exhaust gas recirculation (EGR) valve. Before starting the engine, locate and disconnect the valve's electrical wiring connector. Then start the engine and drive the vehicle to evaluate the radio. The 'SERVICE ENGINE SOON' telltale will be illuminated, and the engine may or may not operate very smoothly. Once you have completed the evaluation, shut down the engine and reconnect the the valve's wiring connector. Then use the onboard diagnostics to clear the PCM codes that will have become set by taking this action with the EGR.

If the AM interference source still has not been isolated, then the next step to try is to disable the transmissions's electrical actuator circuits by disconnecting the wiring connector into the transmission. This is a light gray plastic connector located on the left front face of the transmission; the connector is circular and will have square "serrated" squeeze tabs on opposite sides; you sqeeze the tabs together while pulling on the connector to disconnect it. You may have some difficulty locating this connector. When examining my father's '97 Deville, I could not see the connector when looking down from above; you may need to first remove the black plastic trim panel that spans the top of the condenser/radiator area. (Do not confuse the trasmission connector with a very similar one located directly above the transmission; the second connector looks the same, but does not "plug in" into the transmission.) With the connector disconnected, the transmission will default to second gear; the vehicle will be drivable, but you should exercise caution while driving it and spend as little time as necessary to perform the at-speed radio evaluation. As you can probably imagine, this action will also cause many codes to be set, and there will likely be warning messages on the DIC. Once again, clear the codes after restoring the original conditions.

Try out these ideas and let me know what you find.

The bad news is that even if you do manage to isolate the interference source using these techniques, actually fixing the problem may not be practically feasible!

[Bruce Nunnally]

I always enjoy very detailed and well researched posts, so hopefully we'll still get to hear detailed thoughts on appropriate issues. I do sympathize though that I HATE to research stuff then have the requester be too busy to hear the answer or some such.

[The_Raven]

Howyadoin RDWRIOR,

Please accept my thanks for serving as the conduit on this.

Thanks also for the research into the e-mail archives. I'm an engineering supervisor (controls software and automation), who is also largely responsible for communications with my company's field service staff. I well appreciate people who can make sense of the information provided them and give concise, reasonable explanations and advice.

I'll give the EGR a try first and see what happens.

The tranny disconnect? I'm gonna play Marlon Perkins to my mechanic Mark R.'s Jim Fowler on that one... You know, like supervising the operation from the Land Rover while ol' Jim gets to tattoo a wolverine or something?

I'm seriously thinking about replacing the radio with an aftermarket unit, since it's not the Bose system it seems like a lot less work to replace, making it more worthwhile. Would an aftermarket radio suffer from the same RFI, in your opinion?

I have a friend who is a radio repairman, he restores antique sets and such, perhaps he'll be able to sniff out the source of the RFI with a directional antenna? I only have to drive the car at a couple miles an hour to trigger the interference, he can walk beside the car with the beam, maybe, or use it in the interior. Would the right rear shock sensor be the most likely candidate, being so close to the antenna? Let's see, where did I leave that Pringle's can...

I'm sorry, I'm laying a stream-of-consciousness deal here...

Thanks again!

[RDWRIOR]

Mark,

The trial and error work performed by the original "complainant" (Richard K.) appeared to rule out the suspension control systems as a possible root cause of the AM radio interference problem, even though that seemed like the most likely candidate based on his observed symptoms. A number of other possible "sources" were also ruled out in this process.

Actually, the EGR and transmission circuits (line pressure control solenoid, or "force motor") seem like "long shots", too. So, before you try disconnecting anything, you might want to carry a portable, battery-power AM radio with you in the vehicle and see if that radio also exhibits the same type of interference that you can hear in the OEM radio. If so, then the interference truly is a "radiated" phenomenon, and it would seem very likely that an aftermarket replacement radio will pick up the interference just the same as the OEM radio, especially if you use the original antenna. If not, then the radiation may be localized to the OEM mast antenna. Otherwise, the problem could actually be an internal problem with the OEM radio that will not be present in the aftermarket replacement.

Another possibility is that the root cause of the interference is "backway" noise present on the B+ wire into the radio, which is then appearing in the audio output signals. If this is the case, why does it affect only the AM performance, and no other "playback" mode? Even if this is the root cause of the problem, it may also affect the aftermarket replacement radio if the same B+ wire is used to provide power to the new radio.

This is a very frustrating problem -- there are no obvious answers and no guarantees of any fixes. The best that I can offer is for you try out the things I have suggested above and report the results. Hopefully we can find a solution.

[The_Raven]

Howyadoin,

D'Oh! I tried a little transistor radio in the car today and got the same RFI on AM that the car stereo is getting. Again, there's no interference until I'm moving (either in Drive or in Reverse, haven't tried Neutral yet, but I will), over a couple miles an hour. It appears that the signal is being radiated from somewhere. Would an RF choke on the antenna lead be any help?

On a (probably) unrelated note, the last day or two I've been getting a sporadic clicking sound from the vicinity of the steering column, sort of a Geiger counter-type rapid-fire clicking. I don't know if there's any relationship, but thought I'd mention it.

Thanks as always,

-Mark P.

Salem, MA

[RDWRIOR]

Mark,

Thanks for your feedback on the portable radio test results. It confirms what was suspected from the very beginning: the AM radio interference is caused by radiated emissions from something in the vehicle. This rules out the possibility of an internal radio problem, or "backway noise" present on the B+ wire to the radio. Unfortunately, it also means that an aftermarket replacement radio will almost surely exhibit the same levels of interference.

Installing an RF choke in the OEM antenna cable may eliminate the noise, but even if it does, the question remains: what the h*ll is causing the interference! Since the radio noise is only present when the vehicle is in motion, every vehicle electrical system that was somehow "speed related" was identified. The "trial and error" work that was performed by Richard K. last year seemed to rule out most of these, except for the EGR and transmission pressure control solenoid circuits, which were never checked before he sold his car. If neither of those checks (described previously) eliminate the noise, then it must be that some other, unexpected circuit is causing the problem. By the process of elimination, we should be able to identify the root cause, unless the cause is something truly odd, like "electrostatic discharge of the tires" or such. . .

For your next test, try this:

On a vacant street, drive along at a speed slightly greater than that to produce the radio noise and confirm the presence of the radio noise. Then shift the transmission into neutral. Did the radio noise stop? If not, switch off the engine while coasting in neutral; the radio should remain on when you do this. Is the radio noise still present? Please post the results of this testing, which may help me determine if the cause of the interference is related to the powertrain, and (hopefully) which specific part of it.

Regarding the noise in the steering column area, I can offer no explanation. Is that noise speed dependent? Is it present even in a park/idle condition? Is it related to movement of the steering wheel?

[The_Raven]

Howyadoin,

The interference remains regardless of gear or direction of motion. Shutting the ignition off while rolling in neutral does stop the interference.

I drove around while waving the the portable radio around the interior. The portable radio emitted a good strong shriek which made it easier to identify the presence or absence of the noise. My observations indicate that the noise is constant on level ground, but modulates up and down in frequency when driving over gently undulating pavement. Heavier bumps didn't seem to have as great an effect on the shriek.

When stopping, the sound stops for a fraction of a second, starts again briefly as the weight shifts back to the rear wheels, and then stops like it was never there.

The relative volume while moving the radio around seems to indicate the interference is coming from the passenger side rear, somewhere on a line between the driver's seat and the antenna.

My gut feeling is that the problem is either coming from the ELC or RSS. Which fuses in a '96 SLS need to be removed to disable these systems for testing, or can I do it through the DIC diagnostics?

Thanks for your patience and support,

-Mark P.

Salem, MA

[JimD]

Howyadoin,

....Shutting the ignition off while rolling in neutral does stop the interference....

-Mark P.

Salem, MA

Interesting process, guys. The RF noise might not originate within the car, but may be one or more tires.

Is there any noticeable (measureable?) difference on a concrete Interstate surface with rebar vs. a county road with no rebar?

Keep after it!

[RDWRIOR]

Mark,

Thanks again for your quick reply regarding the "road test" I had proposed.

Your observations regarding the radio noise and the suspension motion coincide perfectly with the observations of Richard K. when he tried to determine the root cause last year.

At that time, the issue was discussed with "HEK", the GM engineer who is the equivalent of "bill bobynski" in matters of Cadillac radio interference. (In fact, "HEK" and "bill" were once colleagues in the "old days" of the Cadillac Motor Div.) "HEK" first thought that the root cause of the radio interference was the control module for the road sensing suspension (RSS) system, which is powered through an 'RSS' fuse. Unfortunately, it turned out that Rickard K.'s "base" '96 Deville was not equipped with that option (RPO 'F45'). Then, it was speculated that the cause was the rear electronic leveling control (ELC) system, which is powered through a 30 A 'ELC' circuit breaker (for the compressor motor)and a 10 A 'ELC' fuse. It was recommneded that Richard K. remove the 10 A fuse, but he claimed he could only find the 30 A breaker. In any case, removing it had no effect on the radio interference, and removing either the fuse of the breaker should have disabled the ELC system. That test seemed to rule out the ELC system as the cause of the radio noise.

After that, "HEK" was essentially stumped, which led to more "trial and error" fuse removal tests by Richard K. based on speculation that the noise was caused by some other "speed related" circuit, such as cruise control and ABS. As I stated in previous posts, none of these tests were successful, although the EGR and transmission checks had not been tried before the '96 Deville was sold.

Assuming that your SLS is equipped with either ELC and/or RSS, you can try removing the appropriate fuses to see if that eliminates the noise. (Apparently, the ELC and RSS fuse protection devices are located in the trunk area, near the back of the rear seat, but I can't give you any more specific instructions on how to locate them. Perhaps this is described in better detail in the owner's manual?) However, I don't expect that disabling the ELC and/or RSS will have any effect, based on the past experience of Richard K. You could also still try the EGR and transmission disconnect test methods that were described previously.

Before doing any of that, however, try this:

Repeat the low speed "road test" that you performed earlier. With the vehicle rolling in neutral and the engine switched off, rotate the ignition switch back to the "RUN" position, but not to the "CRANK" position, so the engine will still be off. You had indicated that with the engine off, the radio noise goes away. So, with the engine off, but the ignition switch back in "RUN", does the radio noise return immediately? If so, is the noise continuous, or does it appear briefly and go away again? Try this test and post your observations.

[KevinW]

When stopping, the sound stops for a fraction of a second, starts again briefly as the weight shifts back to the rear wheels, and then stops like it was never there. 

I think you're on the right track with the RSS system. At low speeds or when you touch the brake pedal, it goes to firm mode, in which case there's no current flow. The fuses are indeed in the trunk compartment fuse block - 10 (IGN+) and 20 (B+) amp mini fuses, both labeled RTD (Real Time Damping?).

Unfortunately, it turned out that Rickard K.'s "base" '96 Deville was not equipped with that option (RPO 'F45').

My understanding is all the regular 1996 models (except Fleetwood) had the RSS as standard; the sportier versions had the CVRSS.

[RDWRIOR]

My understanding is all the regular 1996 models (except Fleetwood) had the RSS as standard; the sportier versions had the CVRSS.

I do not know for certain what the situation was for '96 models, but my interpretation of the '97 Eldo/Seville/Deville service manual (which I am looking at right now) is that ELC was standard on all three models, but CVRSS (RPO 'F45') was optional and/or available only on certain models. The service manual shows diagrams for ELC with and without CVRSS. When CVRSS is present, the ELC compressor is controlled by the CVRSS control module, which also receives the inputs from suspension position sensors at all four wheels. With ELC only, there is only one (rear) position sensor, which directly controls the ELC compressor.

The '97 manual only refers to one active damping system, which it calls CVRSS; there is no RSS.

I know for a fact that my father's '97 Deville is equipped with ELC, because I have heard the compressor operating. I also know for a fact that the vehicle is not equipped with CVRSS, because I have noticed (when performing oil changes and front chassis lubrication) that the front suspension lacks the position sensors -- the brackets where they would attach on the struts are present, but the sensors are not.

A GM VIN search that was performed last year confirmed that Richard K.'s '96 Deville was not factory equipped with RPO 'F45' -- a fact which he independently confirmed by checking the vehicle's service parts RPO tag. He did find circuit protection devices labelled 'ELC' but nothing for 'RSS' -- this suggests that his '96 Deville was essentially identical to my father's '97 Deville, and definitely lacked any sort of RSS/CVRSS. That being the case, how could that (nonexistent) system be the source of the radio interference? Even if Mark's '96 SLS has a RSS or CVRSS system, why are his radio symptoms identical to those of Richard K., if Richard's car lacked the system?

Perhaps the situation was different in '96? I really don't know, and I do not have ready access to a '96 service manual. If anyone reading this does, please look in section 8A ('Electrical Diagnosis') of Book 2, under 'Electronic Level Control' and 'Suspension Controls' and post your findings here.

I've kind of been trying to make this point from the beginning in this thread: I believe the RSS/CVRSS "angle" -- logical though it may be -- was ruled out as an explanation some time ago, although I freely admit I may be wrong. . .

Hopefully Mark can perform the follow-up "road test" that I described in my last post, and hopefully the results will shed some more light on the problem.

[Marika]

This may or may not apply but I know someone who had the same problem in their car, albeit, the car was not a Cadillac.

They figured out that something was wrong with his alternator and after they replaced the alternator and all the wiring to and from the alternator and all the wiring to the other equipment associated with it (battery, starter etc.) the problem went away.

Apparently one of the most common causes of interferance for AM radio, besides flouresent lighting and leaking electrical wiring is electric motors and essentially, an alternator is an electric motor.

Just something to ponder.

[The_Raven]

Howyadoin,

Sorry I haven't had the chance to do the neutral roll with the ignition in "run"... I was cooped up in my recording studio all day yesterday. I do the engineering work in the studio, so you can imagine how crazy noisy audio makes me!

I'm doing a bunch of driving today, so I'll be able to do some more testing today and report back.

Thanks as always,

-Mark

P.S. Are there build codes that will help determine what equipment is installed? Those are located in the trunk, right?

Thanks!

[KevinW]

I do not know for certain what the situation was for '96 models, but my interpretation of the '97 Eldo/Seville/Deville service manual (which I am looking at right now) is that ELC was standard on all three models, but CVRSS (RPO 'F45') was optional and/or available only on certain models.

RSS on the base DeVille was unique to the 1996 model year. For 1995, Speed Sensitive Suspension (SSS) was standard, and the following year (1997), the electronic suspension was dropped altogether. My 1996 E/K service manual shows the ELC integrated with the RSS module. The 1996 Dealer Sales book also shows the suspension as "Road Sensing - Real Time" on the regular DeVille, and the continuously variable version on the Concours; this is consistent with the information in the 1996 sales brochure.

I suspect the RSS has a different RPO code; it would be interesting to see what Fxx codes (or could it possibly be "Z55"??) appear on the SPID label! I'm also anxious to see the effect of removing the RTD fuses.

[RDWRIOR]

Kevin,

Thank you for your very helpful reply concerning the suspension options for MY '96!

It seems to corroborate what the GM "expert" ('HEK') suspected when he was first approached with the complaint long ago -- that the RSS system was the root cause!

However, it is puzzling why Richard K. could not locate any fuses for the system in his '96 Deville, which led us to assume that his vehicle was not equipped with that option.

Anyway, with this new information, I strongly suggest that Mark locate and remove the appropriate RSS/RTD fuses(s) as previously described by Kevin, and then road test his SLS again. Hopefully this will confirm what was suspected from the very beginning of this "project" one year ago. With confirmation, I hope 'HEK' can suggest a "field fix" to remedy the radio interference.

Please keep me informed of the results. . .

[The_Raven]

Howyadoin,

In an example of the irony that permeates my life, I caught a cold... from my doctor.

I'm laid up this morning, but I'll have some results shortly. Thanks for sticking through this!

-Mark

[Marika]

Talk about odd....

I decided to test and see if my 92 Seville also displayed interferance on the AM radio.

What I noticed was that while in PARK or DRIVE there was none, when I shifted to NEUTRAL, the interferance appeared and when I shifted back to PARK or DRIVE it went away. Shifting to NEUTRAL brought about the interferance, but not to the point where it drowned out the station, but you could hear a definate difference in the amount of white noise. Regardless of what station I tuned to, the noise was consistent.

Is there a small electric motor inside the transmission?

[The_Raven]

Howyadoin,

EUREKA! Found the source of the RFI!

Had the car at the garage tonight, and did some further diagnosis on this problem. First we tried shielding the antenna by wrapping the base in cloth, then wrapping two layers of aluminum foil around that and grounding that to the same ground as the antenna. That had a minimal effect at best, seeing as how this RFI really blasts pretty strong.

Next step was to remove the ELC fuse from the trunk fusebox. This had no effect on the RFI.

We found that pulling the "RTD" fuse at the trunk fusebox eliminated the RFI completely. Of course, it also threw the ever-popular "SERVICE RIDE CONTROL" in the process...

We also did some scanning with our handy-dandy RF detector (cleverly disguised as a Radio Shack pocket radio), and found the RFI was blazing strongest in the area noted in the attached picture. There was no RFI to be found in the wheelwells or anywhere outside the cabin and trunk, so I think we've go this pinpointed.

The next question is, of course, what the heck is that module, and how do I replace it? I've tried before to remove that trunk panel and it was not very cooperative. Does the rear seat have to come out to access it from that side?

Thanks as always!

-Mark P.

Salem, MA

[The_Raven]

bump

[RDWRIOR]

Mark,

I am glad that you have been able to confirm that the root cause of the AM radio interference is the RTD module.

As I described in a previous post in this thread, I have discussed this issue further with my expert colleague, 'HEK'. Based on what he has told me, however, there does not appear to be an easy solution to your problem. Apparently, the radio interference is a product of the "slew rate" for the control signals from the RTD module to the actuators in the suspension dampers. The slew rates are set by the internal hardware and software of the module, and there is no practical way to change them.

'HEK' suggested that the first thing you should check is the antenna's ground connections. Make sure they are tight and corrosion free. Then check the antenna cable's connection to the antenna for the same concerns. If neither of these checks yields any improvements, then fabricating a grounded foil "shield" over the module and its wiring harnesses may reduce (if not eliminate) the interference. Unfortunately, you will have to do some experimentation in this regard. . .

As to the process for removing the RTD module, I have no personal experience in doing this kind of work on Cadillac models of your vintage. However, I did consult the electronic service manual for the '98 Deville, which should be identical to your vehicle. It suggests that the RTD module can be removed from inside the trunk by first removing the trunk "bulkhead panel" that is shown in your attached digital photograph; there is no mention of a need to remove the rear seat. Unfortunately, it offers no explanation of how to actually remove the bulkhead panel, and I understand that you could not determine a means of removing the panel in your vehicle. Hopefully someone else reading this thread has actually been able to remove the panel before and can offer some practical tips.

You have stated that you intend to replace the RTD module. Based on my colleague's explanation, I am unsure if replacing the module with a new one will offer any improvement. I suppose it can't hurt to try this out, but I imagine that a replacement module is very expensive, and that you won't be able to return it for a full refund if it does not fix the problem.

Also, my colleague remembers that the AM interference produced by the RTD module was not particularly strong; it was perceptible only when listening to weak or moderate stations. How would you describe the "pervasiveness" of the interference in your vehicle? Is it present on all AM stations, regardless of station signal strength? Or, do you notice it only on weaker stations, which just happen to be the ones that you listen to regularly?

[The_Raven]

Howyadoin RDWRIOR,

Thanks for checking back on this!

We've checked the antenna ground and cable, all is good there. I'll try shielding the RTD module if I can get the panel out, shielding the antenna base was not very effective. My shielding technique would be to wrap the module in cloth to insulate the foil from contact with the module, duct tape it on so all metal is covered, then wrap the module in aluminum foil , solder a wire to the foil, then connect the wire to ground. Am I missing anything?

If replacing the RTD module is necessary, is it safe to assume that I could get a module from a junkyard? Any '96 with CVRSS would be OK to use, assuming the RPO suspension codes match, no?

Also, regarding the relative strength, the RFI is pretty strong... it drowns out even the strongest local stations once you get 30 miles or so from the transmitter. When I use the pocket radio, the shriek of the RFI when the radio gets within a foot or so of the module blows away just about anything.

Thanks as always for your knowledge and patience!

-Mark P.

Salem, MA

[RDWRIOR]

Mark,

The shielding technique that you described for the RTD module should be more than adequate. In fact, it may be overkill, especially since you are in the mode of experimentation at this point. A relatively simple foil overlay with a ground wire should be an adequate starting point to determine if a module shield has any real effect on the radio interference. (It may have none!)

Actually, testing the integrity of the module case's ground may be the best first step. Perhaps you can measure the continuity of the case to a wired ground point. Simply adding a ground strap to the case may be very effective, and then you may not need to make an additional shield.

Try to use an actual woven braid conductor for the ground strap, if at all possible, as it will offer lower inductance vs. a "traditional" round wire.

If the shielding of the module has little effect, then try adding shielding around the wiring harnesses leading out of the module and branching to the actuators in the suspension. (I realize that this will not be easy.) Don't be consumed with making the shields perfect and durable until you can judge their effectiveness in reducing the radio interference. You wouldn't want to invest a great deal of time "over engineering" the shields only to find that they offer little improvement.

Try out the shielding, and report the effects. If there is no real improvement, then trying out the addition of capacitors across the power and ground inputs to the RTD module may offer improvements.

If you can try out a salvaged RTD module from another vehicle, then it can't hurt to try. The module from another '96 model with similar options should work, but you may want to locate and record the part number from your existing module to match to any replacement. Keep in mind that the reason that your vehicle seems to be worse than my expert colleague tends to expect could be due to an internal "durability" problem with the module, such as a broken solder joint or a defective capacitor. Another "high mileage" sample from a salvage vehicle may exhibit similar symptoms, even though it is otherwise functional, whereas a brand new replacement module may not. However, I just do not have enough confidence that a brand new module is a likely solution to your problem for me to recommend that you spend the "big money" for this type of part.

Good luck!