: What next? PCM shot or something I'm missing? Please help.

07-15-05, 01:19 AM
Perhaps you saw my earlier post regarding wild idle on my 95 sls: http://www.cadillacforums.com/forums/showthread.php?t=45720
Well, I've replaced a knock sensor and the ISC motor and the symptoms are still the same.

So I read out PD01 (Throttle Position - Degrees) and it is jumping all over between 12 and 25 sometimes jumping to 45 or 55. I go out and pull the connector from the sensor and no change (it still keeps jumping around just the same).

I measure the dc voltage at PCM terminal 1B15 (throttle position sensor input) at the PCM and it is going from .2 to 1.8 vdc through the range of accelerator pedal position. The voltage corresponds with the pedal, but the pd01 reading just keeps jumping around randomly as before. I also checked the voltage at pcm 2c1 (sensor return) and it was rock solid at .2 volts through all accelerator pedal range.

I'm also getting a P026 (shorted throttle position switch), but I'm sure that's because the PCM is calculating my throttle position around 30 degrees when my foot's off the pedal.

I'm still fighting the P132 (knock sensor problem). It's input votage is supposed to be between .3 and 4.2 vdc, but it is riding up around 8 volts. I've traced that circuit, and I'm pretty sure its intact.

These problems happened at the same time. I'm $167 into parts replacement and dreading buying a new PCM if that's not the problem. Do you think the PCM should be next? I've given it bbob's rap test and no change. Will I have to get the PCM programmed by a pro or will it just work when I plug it in?

Thanks in advance. I really need the help!

07-15-05, 01:18 PM
Check the wiring harness to/in the intake. Follow it down and take the wrapping off the end under the throttle body and see if the insulation is coming off some of the wires.

07-15-05, 10:59 PM
Check battery voltage to the PCM at 2c4 & 2d4 (CKT 480)ORN.

07-18-05, 01:33 PM
Don't rush to change the PCM. The manual should have a trouble tree to help resolve a problem. What happened if you disconnect the trottle position sensor? In that case the voltage on a PCM side should not jump at all.
Anyway, even if the PCM is bad, you should not change the PROM. Only the PCM. And you can find it on-line used for $50+. I changed my PCM this way and now it's fine.
P.S. You MUST use your old PROM in new PCM.
But again, don't change the PCM without more analysis yet.

07-18-05, 11:25 PM
Thanks for the tips, I'll dig in again on Tuesday and post my findings. This help is greatly appreciated!

07-19-05, 06:46 PM
The Oldgamer says that he bot a pcm for $50.00. I would like to know where he got that. All I'm seeing are about $250.00

08-18-05, 01:38 AM
Follow up:

Well, I dug in on the Tuesday I said I would and was simply stumped. The voltages at the TPS and Knock Sensor Inputs were way out of whack. I replaced the knock sensor previously with no change then the ISC (Idle Speed Control Motor) - still no change. I cut the wire for the input of the TPS and the voltages were about 1 to 5 as expected. I then decided I would change the PCM. I found one on ebay brand new for $98 shipped. I forgot to check the transmission fluid life indicator before I replaced the PROM, but I managed to reset the warning.

Anyways, the problem was in the computer. The car is fixed. My gut feeling in the beginning was computer or a major harness failure. My conclusion is if you experience a ton of codes and the computer has b+ and ground where it should, it is likely the computer. 45 days out of commission and $167 in unneeded parts could have been averted if I just would have swapped the computer out.

Anyone know where I can cash in my PCM core?

Thanks for all the help.

08-22-05, 01:13 PM
The Oldgamer says that he bot a pcm for $50.00. I would like to know where he got that. All I'm seeing are about $250.00


08-22-05, 01:29 PM
delzy, two bits says that if you plug the old PCM back in, it will work also. The symptoms you described were of bad or loose connections which you might have cured by plugging and unplugging the PCM.

08-22-05, 06:53 PM
Pay up!! I did reset all the connections twice. I thought that was it when I started. But you can keep your $.25 (if you want to buy my "good" PCM for $50). I'll even ship it to you for free!!!