Transmission DTC woes
This vehicle was refered to me by a local transmission shop. The van intermittently goes into limp mode (stuck in second gear) And sets a P0760 code. When this occurs the PRNDL display will blink for a split second (boxes appear around all the letters). If you cycle the key off and on it will reset sometimes. You know it didn't reset if the PRNDL blinks when the key is cycled on.
Checked the resistance of the solenoids using C4 at the PCM.
Pins 19 and 1 1.5ohms
Pins 19 and 2 1.5ohms
Pins 19 and 6 1.5ohms
Pins 19 and 10 1.7ohms
Resistance spec is 1-3ohms
None of the resistances changed while wiggling/tugging on the harness or connector at the trans.
At this point I decided to scope the control side of the OD solenoid circuit (YEL/GRY wire treminal 1 in C4 at the PCM). I used the scanner to activate the solenoid and the scope showed an pretty even square wave. I then ran the vehicle until it went into limp mode and I noticed the voltage through the solenoid dropped off to zero.
I moved my test point to terminal 19 in C4 at the PCM which had no voltage. I proceded to then test the circuit at terminal 26 at C2 at the TIPM which also had no voltage during a limp mode occurance. At this point I wanted to see what the relay control side was doing and connected a probe at terminal 10 of C1 at the TIPM.
This is where I'm getting lost. When the trans goes into limp mode both voltages dropp to zero, but based on the schematics I've got terminal 10 in C1 at the TIPM should stay hot all the time. We thought the relay could be bad, but it has done the same thing with three different relays. Anyone have any ideas?
The traces I uploaded were taken from the YEL/BRN wire Term 10 in C1 at the TIPM and the YEL/GRY wire Term 1 in C4 at the PCM.
I noticed that there appears to be a pretty steady glitch in the YEL/GRY circuit until the OD solenoid is commanded on steadily. There also appears to be some kind of fluctuation during the initial OD activation. Then when the trans goes into limp mode both circuits drop to zero volts.
What kind of van? Its not posted. Wiring diagram indicates Honda probably. I can tell you I had one of these a few months ago on a V6 Accord. Throwing the same code at like 70k. Old woman drove it. I ended up replacing the wire from the module to the valve and it fixed my problem. Couldn't find inside the harness where it was bad.
We need to know what van you have here, but the wiring diagram shows it to be a Mopar product. Dodge/Chrysler PCM strategy powers off the transmission relay when a trans fault is detected. By doing so this puts the trans in “limp in“ mode. Terminal 10 at C1 should be grounded at all times unless the PCM detects a fault. Once P0760 is detected the PCM will shut the ground off de-energizing the…
Hi Kyle: Want some unsolicited advice? Assuming that all modules have been checked for Active or Stored codes, I'd verify Original vs. Current VIN in all modules. If you have wiTECH, use the Loss of Comm Test to see if you are getting dropouts from a module. HTH, Guido
Classical VSS behavior.Put a scope to it and see what happens.
Based on what you wrote and the code, I would be replacing the solenoid pack. When the PCM recognizes a fault it will shut power off from the relay. You could try scoping one of the other solenoids that are working and comparing it to your suspected bad one.
When I run into solenoid faults on these I will scope the current for the faulty solenoid. Compare it to another solenoid that is not setting faults. If the current is low for the OD solenoid then the PCM is at fault. If the current is the same it is a solenoid issue. I have replaced both tons of solenoid packs and PCM’s for solenoid faults.
Hey Benjamin, I did scope the solenoid circuits and all of them were pretty much spot on the same current peak draw. We went with a solenoid pack and so far so good.
There times when the resistance check on the solenoids won't give up the bad solenoid. Here's what i do back probe pin 10 at the transmission get you a light that carry's a load hook one lead to ground one lead to pin 10 turn the key on it should light the light for a second are so if so the tipm is doing its job. Next back probe pin 19 at the transmission this time hook one lead to power and…