1996 no overdrive

B

bd blk 12v

Fixen broken bulldogs
Joined
Sep 10, 2008
Messages
241
Hello. I have a 1996 2500 with 352k on it. The truck will not shift into overdrive. The lockup works in 3rd gear. I have tried troubleshooting the problem. I have an old snap on 2500 box scanner that I was able to use. The scanner read 281 degrees Celsius. I bought a new trans temp sensor. I homed the old one and new one and they were close to the same. I went ahead replaced it and no change. My scanner now won't read the obd2. Is there a possibility the PCM could be at fault? I have one from a 97 that did work. Would it be worth a shot to change for a test? The gauges and charging system work. The trans shifts fine just no od. Thanks for the help.
 
Have you ohmed out the O/D solenoid from the plug in the trans yet? Could be a bad solenoid, ripped O/D seals, output shaft speed sensor possibly. Did O/D just stop working one day or did it start out as an intermittent problem and did it ever feel like it may have been slipping?
 
Or a bad wire from the PCM to the trans on the ground side of the solenoid
 
The trans has never shifted into od. It doesn't even try. It shifts fine all the way to third, then lockup. I used my snapon 2500 to see output speed was reading fine. I just noticed it showed the temp hot and know it will keep it from shifting to od. I appreciate the help. Where is the od solenoid located? The fluid is also clean and not burned. Thanks
 
OD solenoid is on the VB. You can ohm it without pulling the pan though on the plug on the side of the trans
 
both OD and TCC solenoids will read 20-25 ohms. i think vb has to come down to change them.

they share a common power wire and the PCM supplies ground individually. if youre getting lockup, youve got power to the pair. the high temp is probably the issue.
 
are light throttle upshifts normal or is it hard to get the truck to go up a gear when just cruising along?
 
It shifts light throttle shifts fine. Just crusing it shifts to second well and third well also. It locks 3rd just never tries od. If you get hard on throttle on take off it shifts slow but they all seem to stock. It just doesn't slam them like a shift kit its not solid but does work. I will ohm wiring to ground and see I have a pcm to try may throw it in for fun.
 
Have you thought about wiring in a manual od switch to see if its internal or just an electrical issue ?
 
i think the best thing is to tee into the OD wire right at the ecu plug on the passenger side. i use a bullet connector there and can insert various wires or probes for testing or command of solenoids. this location allows you to test ecu by feeding it batt+ power through a test light into that port and watching to see if it lights when driving. if so, that proves the ecu is grounding and calling for OD.

you can pull the trans relay out of the pdc socket and probe for continuity from there to the test port. this would check the entire length of wire to and from the test port. if u jumper the solenoid relay pins that are closest to the battery then check for power at the test tee that will also prove out the solenoid.
 
It is possible your transmission temperature sending unit connector is lightly corroded. Clean up the connections. If that does not help bypass the transmission temperature sending unit by using a 1,000 ohm resistor in its place. The resistor gives your PCM a correct reading for overdrive to work. If that helps you have another bad sending unit. If it does not help at least you ruled a possible issue out for about $1.
 
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An update. I changed the pcm over with no change. I hooked my snap on mt2500 old school scanner to it and it wouldn't pull codes. I was able to perform solenoid tests I checked the overdrive solenoid and I could hear it clicking in the pan. I checked tps voltage at idle and found it to be .36v and wit is at 3.067v. I believe this is low. Would this be a cause of no od? Would it be smart to do the pot mod? Thanks guys
 
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