Engine/Transmission (1994 - 1998) no downshift and no tcc unlock

[TBurow]

i have a problem with my new truck, the trans wont downshift and it will not unlock the converter if i floor it, when i got the truck the converter was bad and the trans was slipping(from not downshifting), i rebuilt the trans and got a goerend converter it still dont downshift or unlock, i replaced the gov solenoid, put a 100 ohm resistor in the 5v ref line for the trans, replaced the valve body, put a resistor in the tps line, checked that the tps is working and still no unlock or downshift. the tps goes to about 3v at wot. is the pcm bad? i can retrieve codes with my snap on scanner, but it wont give data for some reason, it has no codes. is there a flash for this? anyone have a good used pcm?

1996 ram 2500 4x4 with an auto

 

[KMott]

The condition you are describing is exactly how my truck is. But in my case, i prefer it that way since i have a stock torque converter, which wont put any power down. I have eliminated the tps using a variable resistor in its place. There is quite a bit of information on it if you look around this site. i know with my setup the output voltage is a constant 1. 6 volts, which allows lockup around 90km/h, and it wont come out unless i hit the brakes.

The best thing you could do, is get a hold of a shop manual and find out what the voltages should be coming from the tps at closed and wide open throttle. In the book i have here, it's saying 0. 5 to 1. 5 volts closed, and 3. 5 to 4. 5 volts at wide open. But im not sure how this will cross over to your truck. the tps seems to be prone to problems so i would look there.

Good luck, kevin m.

 

[TBurow]

i have ordered a replacement ecm to check if this is the problem since i get no comunication with my snap on scanner. all the symptoms point to ecm failure, i have chainged the value of the resistor on the ground side of the tps and all it does is delay the lockup and still no unlock or downshift. the tps voltage is . 8 at idle and 3. 5v wot. so the sensor is working.

 

[zstroken]

ECM failure shouldn't give you a lockup condition, unless the output is shorted. Before you put your new ECM in. Look at the wiring. I had an issue on the transmission harness on the truck that took out my ecm. Basically all of the insulation had fallen off of the wires and the 12V shorted to the 5V.

 

[TBurow]

i will check it today. but im concerned with the lack of live data on the scanner, i can pull codes but no data.

 

[TBurow]

Fixed

tried the new pcm and had the same results, no comunication with scanner and same shifting way too soon and no downshift or tcc unlock. so having wasted $215 i went out to my old truck and cut the diagnostic port and wired it directly to the pcm connecter and now had comunication, made a new harness for the tps and wrapped it in aluminium tape(heating and a/c foil tape) and wired it directly to the pcm connecter. truck shifts fine all is good hope that is the end of my problems. guess the factory harness is fried somewhere.