SWRC glitch

[rockfangd]

HI all. I have heard of this before but rarely.

I just started driving my 97 SLS and the first time it happened I thought I hit a button or something but the second I knew there was a glitch.

twice now if i hit the select button down SWRC button the phone turns on and disrupts the radio, then the radio switches back for about 30 seconds and back and forth until I turn the phone off.

It has only happened twice so far but I typically keep the center consoe locked so it isnt like I can just shut the car off to turn the phone off.

Everything else works fine I was wondering if it could be just the right SWRC switch being faulty and sending an incorrect signal.

I have a replacement switch setup for the audio so I should be able to just replace the faulty unit if that is the case.\

Thanks all

[Texas Jim]

What is the SWRC button?

[rockfangd]

The button that glitches once in awhile is the select down button, right side of wheel, used for the audio system. maybe should have been more specific.

97 Cadillac SLS

Full Bose system with DSP and changer

Mobile phone and hands free with SWRC

[Cadillac Jim]

I have the same setup on my 1997 and this never happens to me. It sounds like a bad ground, or perhaps a network glitch. Please run the OBD codes and post them here. See the link in my signature block for instructions on how to do this.

[rockfangd]

will do. last I checked there were none

[rockfangd]

U1146 – Loss Of Onstar Communication.

This is the only code that came up

[Cadillac Jim]

That one could be telling us something. I've never seen that one before, but OnStar is the one thing that can turn your phone on when you are doing something else. The first thing I would suggest is that you check the phone fuses. Since analog phones are no longer supported by GM or the cell phone network, you should have NO SERVICE whenever you try to run the phone on. Your problem could be caused by RF interference on the analog cell phone frequencies, which are no longer used by the cell phone providers. I have the OnStar Diagnostic Manual but it doesn't make clear how to enable/disable OnStar, but you can disable the phone using the IPS03 override codes, number 16 (0x01) in my 1997 FSM, page 8C1-21. This is the same override data block as the BTSI notice (Brake Transaxle Shift Interlock) DIC message, "Apply Rake to Shift" message is enabled from the factory by default (and I, as many others, turn off). Beware the possibility of "bricking" your DIC module while attempting changes in these override codes.

[rockfangd]

no blown fuses. phone works fine but shows no service.

So you are saying the phone is worthless? I really like it.

I was yhinking maybe the glitch problem was just a wrong signal being sent when I puahed the select down button, Is that a possibbility and it wouldnt set a code because of its rarity to occur?

I might add that it hasnt done it in 2 days

[Cadillac Jim]

Since there is no analog phone service anymore, the phones on GM cars older than about 2003 won't work anymore. I suppose that there is private cellular service somewhere on private property, and I once detected a weak cell signal near the Ranger Station at the Grand Canyon South Rim, so it's not completely useless. But you can't get a cell phone company to enable your phone and give you a phone number, you can't make or receive calls with it unless you know somewhere that someone has an analog cell operating, and OnStar doesn't want to know you.

There were two phones for 1996 and 1997, a fixed phone with a cord and a portable or cordless phone that uses an RF link to the phone in the car. Other than the handset (one looks like a cell phone, the other has a cord) they are identical. Mine is the Fixed Phone. Which one do you have?

If the U1146 was a History code, you can probably ignore it. I don't have anything on that code in my 1997 FSM, so I expect that it's self-explanatory. If it keeps coming back or you see it Current, follow the purple wire from the phone module in the trunk and see if you can find a break or a loose connector.

I've had the phone come on once in a long while, and every time I've traced it back to the phone not being firmly on the hook in the console, or to something touching one of the SWC switches on the left side of the steering wheel. If you can solve the problem by pressing the SWC switch for END, that is an indication that the SWC switches have been jiggled. I suppose that it's possible for a bad pothole or some such to cause a switch to move somewhere, or some extra slack somewhere in the steering column to allow the SWC switches to be jiggled somehow. But, if it practicably never happens and it isn't a problem when it does, I would ignore it.

I found the SWC schematic on page 8A-152-0 of my 1997 FSM. Each SWC switch control operates two switches, one when pushed up and another when it's pushed down. There are eight switches. When you have a phone the left hand ones operate the phone, otherwise they are HVAC temp up and down and fan up and down switches. There is no electrical difference when there is a phone, just the labels. The way they work is there is a 12 Volt signal from Retained Accessory Power through the 20A Cluster Fuse in the trunk compartment fuse block through an air bag coil (!!!) to eight resistors hooked in series. Each switch connects to one of the resistors. All the switches have their other terminals connected together, and that wire goes through another air bag coil (!!!) to the IPC. Thus the IPC can tell which switch is connected by the resistance to the input. There is a table of these resistances on the page with the schematic.

The SWC hookup, other than going through two air bag coils, is actually pretty simple, and there is a built-in resolution when two switches are pressed at the same time: there is a priority set by how far up the chain of resistors toward the 12 V input that each switch is hooked up to, and the resistance seen by the IPC is that of the highest priority switch. Any switch that is pressed shorts out the inputs to all lower priority switches.

The resistances in the table are, in decreasing order of priority:

Volume Up, 1270 Ohms

Volume Down, 1564 Ohms

Select Up, 1912 Ohms

Select Down, 2387 Ohms

Fan Up/Phone, 3102 Ohms

Fan Down/Recall, 4282 Ohms

Temp Up/Send, 6652 Ohms

Temp Down/End, 13632 Ohms

A resistor to ground of 480 Ohms gives neat steps of about 0.465 Volts between switches, with 0.5 Volts for the Volume Up and Volume Down. So, how could one of the right-hand switches, which gives resistances between 1270 Ohms and 2387 Ohms, give a total resistance of 3102 Ohms or more? Well, a bad contact could do it. If you press the switch gently so that you get a scratchy contact, it's possible that whatever they have in the IPC to deal with that gets fooled once in a long while.

[rockfangd]

I have the fixed unit. see i was wondering if the SWRC switch on the right was not sending the right resistance if it could be misinterpereted as a different button being pressed? hard to explain.

the 2 times it did happen no button stopped it from trying to connect. I had to manually power off the phone. Does holding the end buttton power the phone off?

See unfortunately I do not have the manual for the cellular phone and nothing is covered in the main manual

[Cadillac Jim]

There is a section in the 1997 FSM for the phone, 9I. OnStar is a separate book.

Pressing END hangs up the phone but does not turn it off. The SWC END switch has the same effect as the END button on the handset.

If you had to turn off the phone, the problem may have been in the OnStar module, not the phone itself. The only code you have is an OnStar code, so that is another hint. I have an OnStar manual but it is the manual for the Goodwrench course for techs, not the service manual, and it doesn't address this situation. I'll look at it again tonight.