2005 Cavalier recurring P0122

Well, to start, not sure if anyone has seen my other post on my 88 Camaro but I'm still having problems there too...

Anyways, I also have a 2005 Cavalier 2.2 Ecotec automatic. I have had this car since 2016. I'm not going to lie, it's a bit of a rust bucket... the fuel and brake lines have already been replaced along with the front crossmember. But, that's beside the point.

The 05 has never had a running problem and never thrown a MIL until February, when I had been letting my sister use it. When I first got there, the car was throwing a P0122. 5V checked good and ground checked good, so I replaced the throttle position sensor about a week later (she lives 100 miles from here so it's not like I can just drive across town to fix it and the TPS took longer than expected to arrive). Code went away for a week and then came back. This time it brought along its buddy P0452 (I think that's the number... the one for fuel tank pressure sensor low voltage). She drove it with the codes (really only affects trans shift points and throttle tip in besides torque converter lock/unlock) until she bought another vehicle and I had it towed home 2 months or so ago. I took it to the dealer and put it on a lift and found a short in the tank pressure sensor, or at least in the wiring at the time. Having to wait until the tank was nearly empty and also having to get new hardware for the tank straps (had to cut a bolt to drop the tank), I finally replaced the sensor a little over a month ago now. It was fine for a couple weeks and then the code P0122 came back. Along with the tank sensor code.

I had already bought a junkyard PCM by the time I got the car back. Because, according to the wiring diagrams, the 5V reference and ground buses are common only internally to the PCM... each sensor has an independent signal, 5V, and ground wire. I also cleaned the PCM ground on the cylinder head. Anyways, also having to replace the pass side inner tie rod, I hadn't been able to get it to the shop to have one of the techs do a reprogram on the replacement PCM until last Friday. PCM was put in (with the constant power fuse out, obviously), reprogrammed, and everything was fine. Until the next day. When it threw the blasted codes AGAIN. Thinking there might be a problem with the fuel tank pressure sensor harness, I unplugged it from the body connector yesterday and reset the codes. It didn't even make the 5 minute drive to work this morning without throwing P0122 again. As I was going home, I unplugged the A/C pressure sensor (which is not fun to get at BTW), leaving the TPS as the only sensor on that 5V and ground bus, and reset codes again. And it threw the P0122 again!

1. TPS is NOT shorted.
2. 5V bus has 5.08 volts and is not shorted to ground bus. Measured at both TPS and A/C sensor connectors. I'll try measuring the resistance in the wires when the weather decides to cooperate.
3. Problem is quite intermittent. Sometimes it will go a couple days or weeks without throwing the code, other times the codes will be 10 minutes or less apart.
4. Tank pressure sensor is new. Harness will be checked once I run some more gas out of the tank as I noticed some rodent debris when I dropped it to replace the tank sensor. Sensor is also NOT shorted. At least as of yesterday when I tested it.
5. No indication of corrosion on sensor OR PCM connectors. Or the gas tank to body connectors.
6. Using a Tech II, I have noticed that when the sensor signal drops out, the TPS, the A/C pressure sensor, and the fuel tank sensor signals ALL drop out at the same time. The manifold pressure, coolant temp, and intake air temp sensors are unaffected. I have not seen a code for the A/C pressure sensor even with it unplugged.

Between the 2 cars, I'm beating my head against a wall here. I'm getting tired of having to drive a relative's 2012 200 that Geico refuses to fix accident damage from 4 years ago on that also has an exhaust leak I just don't feel like fixing... I just need this car to last another year, and to do that, it needs to pass the I/M 240 inspection in January, which it's clearly not going to do as of this point, with the MIL on and throwing codes for the throttle position and fuel tank pressure sensors and not being able to clear all monitors. It had cleared all monitors after replacing the PCM, except the Catalyst monitor, when I took it for the drive after replacing the PCM before it threw the P0122 again. But it's going to reset 4 of them every single time I have to clear out the P0122 and the tank pressure sensor code.

Definitely sounds like you're chasing a 5V reference wire shorted to ground. Been there, and it's never easy. Like Paul says, the trick is heat and vibration. It's my experience that intermittent, brief shorts will usually set sensor codes and not 5V reference circuit codes. That's why you're getting a P0122 and not a P06XX.

It sounds like you've eliminated the sensors themselves, which leave the 5V reference wires themselves. I grabbed this from the GM wiring diagram:



Some careful shaking of the harness while watching the 5V reference might be a good next step, as long as you don't get too aggressive with the shaking. Just some gentle pushing and pulling are the trick.

The other option would be to access the PCM connector and remove pins 23 and 25 from C1, and 65 and 67 from C2 one at a time and recheck for the codes. For example, if you remove pin 23 and the P0122 comes back, the short isn't in the A/C Pressure Transducer wiring. But, if you remove pin 65 and the code never comes back, you know the issue is in the MAP wiring.

Make sense? If depinning the connector isn't an option, you can also cut the wire close to the PCM. Somewhere repairable, after you've found the problem.

Okay, been a couple months, same issue. Car is due for both renewal of registration and inspection by the end of the month. Can't renew reg without inspection, can't get inspection if car is throwing codes every 45 seconds.

New TPS installed the other day.
TPS 5v and signal rewired straight from PCM to sensor bypassing entire harness.
J/Y PCM replaced with warranted reman.
Just pulled the tank again to examine harness. After the loom and the tape came off, no wire damage evident. No wire damage evident between body harness connector and rear body connector either. And I would have thought that the resistance of the tank pressure sensor between 5v and ground side would be more than 4.13K? I don't have the chart for P0452 handy at the moment...
Not sure exactly how to pull apart the PCM connectors to get the terminals out... The covers come off easy enough but I'm not sure how to get the TPA locking bars out so I can pull out the terminals individually.
I have no problems on the MAP at all or the IAT.
IDK if I have enough leftover gray wire to bypass all 5v wires on the primary (TPS, FTP, and A/CPS) bus in the engine harness... but that's going to be the next thing if I have to do so after I put the tank back in (going to be fun with a 1/3 of a tank in it). I have all the necessary pinouts for the C100, PCM, and the connectors going back to the rear body connector.

Just wondering if the TPS is adjustable? This is just a quotation from a Google search "Did you adjust it when you installed it? If the signal value is less than .17V then the PCM sets this code.
Read more at: www.obd-codes.com/p0122 "

The TPS on pretty much all GM vehicles is not adjustable after 1990. Not sure about the trucks and anything else running TBI, however. Someone correct me if I'm wrong.

Was looking around the C100 area after I shoved the fuel tank back in and found...

Right at the top of the harness bundle, there was a bunch of wires that seem to have been pinched at some point, all different colors. The worst one was.. GRAY. It had 2 holes worn in the insulation about 1/4" apart. So I cut the tape and pulled back the loom in the part going to the PCM about 10" back, cut the wire, and pulled it out of the harness. I cut out about a 4" section of the wire and soldered in another piece. I couldn't pull the C100 either out of the bracket or apart (I already said the car is a rust bucket and the bracket would have been royally messed up), so I don't know what terminal this wire was in, but wish me luck...