DTC Code P1635

[bluestringer]

2003 Lesabre, getting a P1635 code. The service tech says all sensors, wiring and grounds check out. He thinks it may be a bad PCM. Is this a possibility? What would cause a bad PCM?

 

[Spriteman]

Is the car still starting and running and then dying after 15 mins or so? If it is it's very hard for me to think it's the PCM.

The PCM sits in the air box under the hood and gets the coolest air coming into the engine bay. It's possible, but not likely, that the PCM is being affected by heat and causing it to fail.

The more likely scenario is that the ignition control module (ICM) is getting heated up and it's failing. Have them take off the ICM and look to see if the white thermo paste is still under there. It's probably not - that paste allows heat to transfer from the ICM to the ICM bracket and then to the frame allowing the ICM to not get too hot.

Go to www.car-part.com and search near your zipcode for a used ICM - look under ignition module. You can probably find one for around $35. You can also find a PCM for around the same $$$ - look under computer. You'll have to identify exactly which one you're looking for.

I suggest having the dealer do it and let them pay for the used parts - then when they've found the faulty part they can put a new one of whichever one was failing on the car. And no more time will be wasted - $100 max for both parts is 1 or 2 hours of their shop time. Which is what it sounds like they've already wasted.


BTW - it could still be a bad CKP sensor.

 

[bluestringer]

As far as I know it is still stalling out. They have had it for over 2 weeks now, tech says they have checked everything including the ICM and it's fine. I bought the car from them and only had it one day when it started acting up, so this is on their dime. I thought it was going to be something simple like a bad MAF, which they say was replaced before I bought it. Now after taking this long to find the problem it's got me worried something is seriously wrong with the vehicle. It gave the MAF code and the P1635 when I checked it with my code reader after it started stalling with me.

 

[Spriteman]

Just did a little more research on the P1635 code Circuit 1 relates to the following sensors:

A/C Pressure sensor
Manifold Absolute Pressure (MAP) sensor
EGR sensor

If they've been looking at the MAF sensor that would not be the problem - have them focus on the sensors mentioned above.

Check the grounds at the PCM as well as the main wire harness connector at the PCM.

 

[bluestringer]

I've done some research on it also. Saw where it suggested checking for damage or faulty connections at MAP, MAF, or TPS. Also said to check EGR and fuel pressure switch on Vin K, which mine is not. But it also said most likely there would not be any driveability problems, which mine is having problems. Mine is showing both the 1635 and a MAF code also. IDK, this has everyone stumped. I haven't heard back from them since the tech told me they were going to change out the PCM.

 

[bluestringer]

The saga continues. The dealer techs have gave up. The salesman and manager are now sending the car to an electronics specialist. The salesman said he drove the car to him and it ran fine, but it is stilling showing the P1635 and a mass air flow sensor code. Mass air flow sensor has been replaced twice. The techs could not find any sensor, wire or ground that is causing the P1635. Also the tech claimed he could not find a PCM for the car, which I find hard to believe, but I don't think that's the problem anyway.