4L60E Downshift Problem

BP-MAN · January 9, 2006

Mr. GM-Technician: Have Read Past Tranny Problems Posted,Some Are Close to Mine but NO Cigar ! I Have 1996 GMC SL 1500 4X4,305 Vortec,4L-60E,approx.120,000 Miles. After initial startup the Truck will start out in 1st and up-shift fine,first stop I make it starts back out in 2nd,will not go back into first unless You Manually down-shift selector from Dr.to 1st. Had Service Engine light on but NO CODE, I changed the 1-2 and 2-3 Shift Solenoids,No Good,changed Pressure Control Solenoid and cleaned Pressure Switch Assy. No Good,Took it to Tranny Shop and He Said it was the ECM,I Got Re-Built and Re-Flashed unit from Standard Electronic Parts,Worked Great for 15 Mins. Had No Service Engine Light on and shifted properly for 15 Mins Driving then Light came back on and lost First down Shift Again,When it does Work it Runs Great,Tranny Feels Great ! At every stop after that first up-shift I have to pull the selector into first,pull out then up-shift selector into Drive,If I had a Clutch I would feel like I was driving a 3 on the Tree Again !!!!! I Have heard this was one of the first years for this computer shift and it is a Pain in the ---!!!!! Any Info would be appreciated other than a Gallon of Gas & a Match !!!!! I Thought of that First !!!! THANK YOU !!!!! B.P.

BP-MAN · January 10, 2006

I don't work on tranmissions, but I know enough to be dangerous. First of all, '96 is not the first year for electronically controlled transmissions, but that's irrelevant to what's going on.

I'm having a real hard time buying that the engine light is on but there are no codes. It sounds to me like the PCM is seeing a fault in some electronic component related to the trans and is defaulting it to 2nd gear.

You need to find someone that can tell you why the engine light is on. I'm sure they'll find that it's because of some DTC stored in the PCM and it's probably trans related.

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GM-Tech · January 10, 2006

I don't work on tranmissions, but I know enough to be dangerous. First of all, '96 is not the first year for electronically controlled transmissions, but that's irrelevant to what's going on.

I'm having a real hard time buying that the engine light is on but there are no codes. It sounds to me like the PCM is seeing a fault in some electronic component related to the trans and is defaulting it to 2nd gear.

You need to find someone that can tell you why the engine light is on. I'm sure they'll find that it's because of some DTC stored in the PCM and it's probably trans related.

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And your point is?

BP-MAN · January 10, 2006

I Thank You for Your Prompt Reply !!! I took this Truck for a ride at approx.6:30 PM this evening and it worked Perfect for 10-15 Mins,after a stop sign it shifted from 1st to 2nd a little hard and it went back to screwed up again,the Service Light was on the whole time though !!!!You may think I'm full of You know what,but I was standing there at My Local Repair Shop when He had His $16,000 Snap On Analizer hooked up to read the Trouble codes and there wasn't any !!!! He scanned all the operating perameters and They all showed Good,I've Known Him a Long Time and He was Perplexed Why there was NO Codes,so was I !!!!! I have No GMC Truck Dealer close to Me but I Guess I will have to locate one and see if They can find something with this Truck !!! When I eventually find out what is wrong I will post it to let You know the Fix !!! I Appreciate Your Time !!!! B.P.

Ranger · January 10, 2006

I don't know much about that model of scanner but if it's handheld maybe you can persuade your friend to take a ride with you, hook up the scanner, and when the trans start screwing up again see if it flashes a code on the scanner. I haven't used a scanner before so I don't really know if it'd work that way but that'd be my idea.

GM-Tech · January 9, 2006

I don't work on tranmissions, but I know enough to be dangerous. First of all, '96 is not the first year for electronically controlled transmissions, but that's irrelevant to what's going on.

I'm having a real hard time buying that the engine light is on but there are no codes. It sounds to me like the PCM is seeing a fault in some electronic component related to the trans and is defaulting it to 2nd gear.

You need to find someone that can tell you why the engine light is on. I'm sure they'll find that it's because of some DTC stored in the PCM and it's probably trans related.