Tcm ?
 

I have a 2005 Saturn Ion that is my daily driver. My commute to work is 45 min all highway. At @35mpg it earns it's keep over my gas guzzling GMC Sierra. Car has been pretty dependable. I have only had to do a complete tune-up on it when it started running rough and I had to replace the plastic windshield wiper armature when it failed. Like I said over-all good car. Book value is not much so I do not want to put a lot into it but these days used cars are getting expensive as well to replace.

My most recent problem is crazy. It started out as what I thought a fuel pump problem. While driving down the road the RPM's and speed would suddenly drop. Now it has developed into once the car warms up the automatic door locks start clicking and then RPM's climb quickly like it missed a gear and the speedometer drops to 0mph while it's coasting at a high speed. The digital odometer readout will say POWER STR. After a few seconds everything will correct itself and be fine for a few miles and it will start all over. I am getting the following codes: P0420, P0700, u101, P0717, P1810 P0722 and P0741 (which are all transmission related). I took it to my local transmission shop and they said it is having an electrical issue with communication between the ECM and rest of the car. They said ECM loses power and keeps trying to relearn car. Advised I take it to local shop that specializes in electrical issues. Everything I have seen on line is pointing to the TCM, possibly a grounding issue. I hate to just throw parts at it but I'm thinking about just replacing the TCM and see if that is it. Some folks have advised it might just be a bad battery, transmission fluid level, or even the catalytic converter is clogged up. Unable to easily check transmission fluid level without a dipstick. Anyone else have this issue and know a remedy? I will put the codes below with explanation too.


P0420 - Catalyst system efficiency below threshold bank 1
P0700 - Transmission control system (mil request)
u101 - Lost communication with TCM
P0717 - Input turbine shaft speed sensor A circuit no signal
P1810 - TFP valve position switch circuit
P0722 - Output shaft speed sensor circuit no signal
P0741 - Torque converter clutch circuit performance/stuck off

Im replying because you had good structure to the post, and took the time to identify the codes. So, thank you for that.

The p0420 code is probably not related. Either a bad o2 sensor or the cat is actually getting clogged.

All those trans codes are circuit codes. Which would present an electrical issue, as you said.

Are you capable of doing electrical diag yourself? First, test the battery, make sure its still happy with the voltages.
Next, start directly at the TCM. I do not know pin location off hand, but check for power and ground.

Process of elimination says with 3 no signal codes, the TCM is the culprit.

I'm attaching pdf of the wiring diagrams for 2005 Ion TCM, first page for 2.2L engine, second page for 2.4L engine. I don't see any difference, but I didn't check every wire, pin, and color. Power comes in on pin 31 (ignition) and pin 32 (battery) and ground is on pin 49. Good luck!

Awesome, thanks fellas I’ll start the process of elimination.

Is the TCM outside the transmission or inside?
Check for blown fuses first.
Then check continuity of the wires outside the transmission leading to the TCM and the valve body if it is accessible on the outside. Could be the TCM itself, could be an external wiring issue, could be an internal wiring issue.

Just some food for thought

If I remember correctly, Its outside near the strut tower.

It was a bad TCM. Replaced with one from salvage yard. Runs great again!

Another happy customer