Make sure the PCM is actually requesting O/D first..... be absolutely certain the trans is the problem before replacing it.

 

Is a pinout for the pcm in the service manual? Could the speed sensor on the back of the trans cause a no overdrive situation? Does it matter that I can hit the od button on the shifter and the light goes on and off, but obviously no change in rpm. What about a trans temp sensor? I know it won't go into od if the pcm thinks the trans is to cold.

 

Service manual does indeed have connector pinouts.

Speed sensor on trans also drives the speedometer. If the PCM wasn't getting a signal from it, it would whine about it. (and you would also have other shifting issues.) Yours is a 98 though..... so, pretty good chance that the sensor on the trans is merely the 'output speed sensor', and PCM gets its cue for vehicle speed from the rear wheel speed sensor. (as would the speedo.) But, if the RWSS, and the OSS didn't agree, it should whine about that as well..... (though, it wouldn't be the first time the PCM didn't complain about something that was obviously 'not quite right'......)

O/D button just sends a signal to the PCM, PCM turns on the lite, and then simply won't ground the control circuit for the O/D solenoid.

Trans codes may not necessarily turn on the CEL. May not hurt to get the codes read, and see if anything interesting pops up.

Temp sensor may indeed be a problem. Only way to verify that though, is to be able to read real time data, and see what temp the PCM thinks the trans is. If it though the trans was overheating, it would turn on the trans temp light in the dash.

Think you need to be able to look at real time data here. Trans temp, is PCM actually requesting O/D, etc.

 

First, you are awesome lol. The second is my fault for not updating my sig, and it may not matter, but my truck is now a 2001 with a 360 and 46re. I scan the truck all the time, I never get any codes. Can I find the od pin on the pcm, backprobe the plug and manually apply power to the od wire while on the fly? That would at least tell me if the pcm is telling the trans to switch into overdrive right?

 

PCM controls the ground side of the circuit. The O/D, and TCC solenoids get power from the same source. (thick red wire on 8 pin connector.) If you test the wire, you will indeed see power there, provided the engine is running..... Question becomes, does the PCM actually GROUND the circuit? Would have to wire a test lite in line with the circuit. If the lite comes on, but, the trans don't shift..... either the solenoid is bad, or, you have bigger issues.

 

Ok, sounds like fun. Ill be able to get to do it tomorrow, ill let you know what happens.

 

Backprobe the OD solenoid wire with a volt meter (on the Durango it was C2 pin 21 not sure if its the same on the ram) go for a drive... while in 1st, 2nd, and 3rd you should be getting 12+ volts. When the PCM commands OD it should read 0v. once it downshifts back you should have 12v again.

If that checks out okay then either your orifice filter in the overdrive piston housing is missing or the overdrive piston seals are bad.

Edit: just checked my 97 ram FSM and it says the OD solenoid is B21 (white connector), i assume its the same for 98.

 

You said the od light goes on and off ?, so is the od light blinking when you try and use od ?, if so, then the blinking od light is telling you that there is a problem some were, you just need to figure out what it is.

 

I think he mean that the light goes on and off as he is pressing the OD off button... not that its blinking on its own.

 

With the engine and transmisison fluid cold, disconnect the PCM connectors Terminal #1 of connector B (violet wire) is the trans temp signal. The terminal is numbered on the connectors. Find yourself a good ground. The resistance (thru the temp sensor) should be roughly 2000 ohms with the fluid basically at room temp. If the resistance is much higher than this, then the PCM is seeing a temp that is colder than normal; if the resistance is much less than this then the PCM thinks the temp is higher than normal.