93 ETC goes brrrrt...

[jackc]

Over the past year my 93 has developed an odd problem.

Driving at any speed, I get a momentary buzz and clenching that feels like its coming from the left front. It sounds like the ABS test that the car does when you first start off. It will do it multiple times over a drive of 1/2 to xxx miles.

The clenching is subtle, but pronounced enough to sometimes trip a service ride control message.

I had it in to the dealer a few months ago, but they didn't find anything wrong (but they didn't look very hard).

One thing I do know is that if you watch the volts, there is not a voltage drop when it happens - so I think that's telling me the ABS pump is not activating.

The car is not setting any codes (other than the usual service ride controls that are due to the passive shocks and struts).

The only possibilities I can come up with are ABS activation, or something with the trans.

Has anyone ever encountered this? Or are there any other thoughts about where to go on this?

[BodybyFisher]

You are giving contrary info here, first you say "Driving at any speed, I get a momentary buzz and clenching that feels like its coming from the left front" and then "One thing I do know is that if you watch the volts, there is not a voltage drop when it happens - so I think that's telling me the ABS pump is not activating".

I am not being picky, just pointing out something. Are you sure that the ABS pump would cause a visible voltage drop given the length of time its running?

It is sounding like you have an ABS issue. Does your hub bearing also double as a rotation sensor? The ABS would engage if it sensed wheel spin.

I wonder what condition would imply more wheel spin on one wheel?, besides actual wheel spin

[Cadillac Jim]

I think that it is either mismatched front tires, a big inflation pressure difference between front or rear tires, or a wheel speed sensor (any one of the four). Please give us all the codes. It's best to run the codes right after it happens, without turning the key off. Otherwise we won't get any Current codes.

[jackc]

Thanks for the replies. Below are some preliminary reponses.

I'm just trying to brainstorm through this some. The only possibilities I can come up with that could cause the clenching, other than ABS, might be some unwanted electrical command within the transmission, or a simmering mechanical problem in the driveline where something is wanting to lock up.

Here's my responses to the observations so far:

"You are giving contrary info here, first you say "Driving at any speed, I get a momentary buzz and clenching that feels like its coming from the left front" and then "One thing I do know is that if you watch the volts, there is not a voltage drop when it happens - so I think that's telling me the ABS pump is not activating".

Yes - I understand the contradiction. If I was seeing voltage drop, then I'd be inclined to say ah ha! probable ABS activation. But its not so I'm not.

"Are you sure that the ABS pump would cause a visible voltage drop given the length of time its running?"

No, I'm not.

"Does your hub bearing also double as a rotation sensor?"

I'm assuming that it does.

"It is sounding like you have an ABS issue."

That's what I'm hoping it is - because that sounds solvable. It makes sense that a bad speed sensor in the left front hub could cause the ABS activations on that wheel.....

"I think that it is either mismatched front tires, a big inflation pressure difference between front or rear tires"

All 4 tires and wheels are identical and equally inflated.

"Please give us all the codes. It's best to run the codes right after it happens, without turning the key off."

I'll check for those and report back.

[jackc]

I checked the codes tonight and found 2:

P137 - Loss of ABS/TCS Data, and

I032 - Loss ABS/TCS Data.

Both in history.

After reading in the FSM about I032, and in light of the random ABS activations, I think I'm concluding that the EBTCM is toast.

Any thoughts?

[TDK]

Jack C,

Our vehicles may have some similar issues with the Stability or ABS systems. Please note my post and answers:

http://caddyinfo.ipbhost.com/index.php?showtopic=17753 It was topic'ed about a PZM issue, but the TCS-1225 is a code for a left-front wheel speed sensor, (and it actuates only during a hard start in Drive).

Your codes are differant (OBD-1), but perhaps your problems could be related to a "factory fix" noted for 1997 Sevilles for the TCS-1225.

Good luck!

[vdwarren]

Hi Jackc,

I have a 96SLS, and may have had simular problem. Mine at low speed after just touching the brake pedal, the left front would shudder and release.

I replaced the left front bearing and wheel sensor assy, but found that it was the EBCM.

I sent it out and had it reconditioned, problem solved.

I have a take-off bearing and sensor that tests out fine, "cheap if you need" but the Ranger or Jim can give you the check process to see if the sensor is OK.

Sorry, to get involved with the pro's, but thought my experience may help. Good Luck.

[jackc]

Thanks for the additional thoughts.

I'm still pondering how to be sure this is really an ABS/Traction Contol issue.

I disabled the Traction Control through the OBD system, but the problem is still occurring.

My next step will be to pull the fuse for the ABS pump and see if the problem goes away. I've got to dismantle a couple of things to get to the fuse, so it'll be this weekend before I get that far.

[fivepointohman]

Thanks for the additional thoughts.

I'm still pondering how to be sure this is really an ABS/Traction Contol issue.

I disabled the Traction Control through the OBD system, but the problem is still occurring.

My next step will be to pull the fuse for the ABS pump and see if the problem goes away. I've got to dismantle a couple of things to get to the fuse, so it'll be this weekend before I get that far.

Also keep in mind, not to overlook things like a bad tranny mount and or engine mounts as if they are bad you will get a buzz and or vibration as the motor moves around in the engine compartment.

[jackc]

I pulled the ABS fuse over the weekend, and the buzz did not go away.

So I guess its not the ABS causing the problem.

Both engine mounts have been replaced, along with the dog bones. I did not replace the trans mount, but it looked fine.

I've got a great transmission shop close by, so I may take it there and see if they can zero in on the problem. Or just keep driving and wait for it to get worse......