Can a failing pcm cause Trans problems

BATCH209

MEMBER
2000 CHEVROLET SILVERADO
5.3L
V8
4WD
AUTOMATIC
285,245 MILES

I have a 2000 silverado 4x4 ex cab short bed truck with a 4 in lift. I have a rebuilt 4l60e from Monster with a 1000 miles on it. The other night it started to slip into 2nd gear. This is the same problem that it had in December when monster gave me the go ahead to return that trans for a warranty repair. I don't have any check engine lights on and the atf is still clean just like before. They tried to tell me that I have a bad pcm but the truck runs great. Is this possible and if so how can I diagnose this for sure. I don't want to throw parts at it.

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,645 POSTS

Do you mean the 4L80-E trans? That is the one that came with the vehicle.

Regardless, the transmission shifts are controlled either by the PCM, TCM, or VCM. Now the question is this, does it slip or does it have a delayed shift? If there is a slip (no torque) when it shifts into 2nd gear, to me it sounds like it could be a pressure sensor (allowing trans pressure to drop low) or it could be an internal issue such as a worn intermediate sprag, excessive eccentricity, or the sprag is rolled over or damaged. The only way to check theses items is to remove and take the trans apart. As far as an electrical issue regarding the PCM, one of the other control modules, it should set a trans code. Also, usually the trans doesn't experience a slip, but rather failure.

I would start with checking pressure to make sure it isn't low allowing the clutch pack to slip into gear. If that checks good, I feel it may be an internal issue.

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Wednesday, February 18th, 2015 AT 8:12 PM

BATCH209

MEMBER
2 POSTS

No it does have a 4l60e. That is what my fear was, I never have had so much trouble with any company with a warranty. It looks like I need to bring home my trans pressure gauge and take down the pressures. It slips it revs about 300 to 500 before it engages 2nd gear. The confusing part is no check engine light. And when I had this problem with the last trans it had about 20 on it. There warranty rep keeper telling me that it was a pcm problem. But I had to prove them wrong with the line pressure test and a video of the tach showing it was slipping.

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Wednesday, February 18th, 2015 AT 8:35 PM

JACOBANDNICKOLAS

MECHANIC
109,645 POSTS

Check the pressure and let me know what you find. It could be a simple sensor issue. If the sensor is working at all (sending wrong info) it may not send a code.

I have to be honest, I did some checking before I replied to you. Everything indicates a different trans for this vehicle. Was this something that you changed or was recommended to you? A different trans may be causing issues with the PCM or TCM. Just a thought.

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Wednesday, February 18th, 2015 AT 8:55 PM