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michael, ASE Certified Technician
Category: Chevy
Satisfied Customers: 667
Experience:  17 ASE Cert.; over 20 yrs. exp./18 with GM
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I have a 1994 Chevy C1500 2wd with a 4l60e automatic transmission.

Resolved Question:

I have a 1994 Chevy C1500 2wd with a 4l60e automatic transmission. One day while driving, the tranny wouldn't shift past 2nd gear. I had it put on a scanner and tranny showed to be shifting properly. There are no PCM codes stored. I was told that the PCM , ignition switch, trash in fluid or a broken wire could cause this. Replaced ignition switch, PCM, and checked entire truck for broken wires. Found none. Dropped pan and changed fluid and filter. No trash or metal in pan. No burnt fluid. I reset the computer and the tranny will shift fine, then quit again. My question is , What should I do next? I Can't afford a shop bill.
Submitted: 9 years ago.
Category: Chevy
Expert:  michael replied 9 years ago.

hello. what needs to be done is the ECM needs to be checked for any trouble codes that may be stored in it. your local Autozone or Advance Auto parts should be able to check for codes... and it's free. at that point you can reply with the code #'s and we'll be able to check for what may be causing your issues.



Customer: replied 9 years ago.

Hi, Autozone, etc. told me they can't scan a 94. Only OBDll. I stated in my post that diagnostics showed no codes. (Only a 12 using jumper wire and service soon light) I also have a book of codes and a breakdown of the 4l60e and how it works. None of that helps when the on board computer is not receiving any codes. I can completely unplug the transmission connector and run diagnostics, i get all kinds of tranny codes. I reset computer and plug tranny back up, it shifts fine then stops shifting again. No codes have ever stored when tranny quits shifting. Thats all I know. I was hoping someone in this world had the same problem and could tell me what is causing this.

Expert:  michael replied 9 years ago.

hello. you've stated there are not any codes... yet when you "reset" the computer... it will shift fine again. that in itself would indicate that the computer has set a code that is inhibiting the transmission to shift properly... as is done in most cases when a trouble code sets.


BUT, in the absence of a trouble code... and with the issue that your stating... the most likely cause of this issue would be one of the 2 shift solenoids in the transmission. given the age of the vehicle... i'd recommend replacing both of them and checking/tracing the transmission internal harness to make sure it's in tact.



in the pic below is a data link connector... to be sure we're "on the same page"... your jumpering terminal A to terminal B with the key on and the engine off and letting it flash code 12 at least 3 times... right?



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Customer: replied 9 years ago.
Hi Michael, Yes, I've jumped A & B in ALDL and and SES light flashes 12 three times and continues flashing 12. Nothing else. I pulled the pan again after running truck to test and now I have metal shavings in the pan. It's junk I guess. Now i'll start looking for another tranny. Thanks for your help, anyway.