Not Dave

It's the bane of my existence! Not really. A thorn in my side.

Since I purchased the car a month ago the SES light has been on. Originally scanned it had MAF, misfire and TPS codes. I was able to get the misfire and MAF taken care of. At the inspection station the TPS code was gone but the EVAP code showed up. Found out the EVAP solenoid was full of charcoal so that was replaced and the other parts were cleared out. OK. Back to the inspection station. No SES light for two days! I get there and leave the car. The guy starts it, pulls it into the garage and the SES light is on with code P0123 for TPS high voltage. WTH? Automatic fail. So I go home.

Several days later (I went out of state) I check the PCM to see if the connections are clean, which they are. I had read how someone found water intrusion on theirs and after cleaning the connections it fixed the problem. No corrosion. So I move on to the TPS module and connector. I check the voltage: 0.78 and 4.66 with an even rise while testing. There were no spikes or drops. After testing through about 7 or 8 pulls on the throttle there was nothing to indicate a problem. Consistent. I had previously unhooked the battery to check the PCM so the SES light had been reset.

I start it up, let it idle for a few minutes and no SES light. Shut it down then about 45 minutes later go for a short drive. No light. I even hit it in 3rd gear from 50mph to 90mph, pedal floored. No SES light. Drove fairly normal back home. No light. I'll try it again tomorrow. If the light comes on I'll check the wire going into the PCM to see if it has the same voltages of the wire at the TPS side.

The SES and TPS are a PITA. If it will stay off long enough I can get the car inspected.

Injuneer

To set the code, at some point the signal voltage exceeded 4.90 Volts for one second. Might indicate an intermittent short in the connector between the gray wire and the dark blue signal wire.

Not Dave

Can't rule that out. I did reroute the connector so it had more slack in it between all the other tubes and wires in that little area. Being I've had the P0123 code before changing out the TPS sensor I can probably rule the sensor out.

It was my feeling that sometimes if you disconnect a plug and reconnect that sometimes helps. I visually inspected the 4 plugs on the PCM and didn't see any contaminants in them, they all looked clean and the seals are doing their job. Maybe (my thought) by doing that if there was an anomaly in the connector it has righted itself.

If I continue to get the code I know it's intermittent so could be a grounding issue or what you mentioned. Hopefully if it does come back around it won't be until AFTER it passes inspection, then I'll have a year to sort it out.

I've done a lot of searching both here and other forums on this issue and possible fixes. There are very few posts with the issue being solved. Time will tell.

Injuneer

The short between the 2 wires could also be anywhere in the harness.

GaryDoug

If there were a short, it would be between the gray and blue wires. While that's possible, it's far more likely an intermittent open at pin B (black wire) of the TPS connector. It probably got "fixed" when you unplugged it and plugged it in again.
Even an open inside the TPS or at pin C would give a low voltage, since the TPS input of the PCM has a slight pull-down (~47k ohms). If pin A (gray) or C (blue) of the connector were open, the failure would be P0122 (low voltage)

Not Dave

Didn't fix it. SES light came back on this morning just after I left the house headed to the inspection station. I don't have a scanner, just assumed it's the TPS high voltage code again. I'll get me a code reader soon. Need to get the USB cable and download Doug's software.

I'll check continuity of the lines from TPS to PCM. I believe I'll be looking for some ohm resistance, not sure how to do it. Will google how to check for opens or corrosion on a wire.

I had been on FML leave from work due to my wife having hip surgery so had a lot of time. Now I'm back at work so the car sits until I can find time to work on it.

GaryDoug

You can buy a simple code reader for under $25. This one would work just fine: Note: This is a upgraded chinese-made knockoff of a discontinued version by Autel. If you want to buy a real Autel version (with less capability), here it is:

Not Dave

I picked up an Autel AL309 off Craigslist (local) this afternoon. Got the codes cleared. I've driven about 50 miles so far and the SES light hasn't come on. I understand it takes about 60-80 miles for the light to come on if a code has been thrown.

Clearing the codes also clears the freeze frame data. I'm wondering if I clear the codes then go to get the car inspected will they know and will it fail because the data isn't complete? Of course I couldn't look at the FFD to see what the parameters were when the TPS high voltage code was thrown since I cleared the data first. Now I know. I'll drive it some more tomorrow and when the SES light comes on I'll stop and write down the FFD when it occurred.

If I can simply clear the codes and it'll pass inspection that way then I'll do it. It still has high idle surge at times. According to the tach it shows about 1,350 RPM at idle. Actual through the monitor shows about 800-820 RPM. The car's tach is off by quite a bit. When it idles high the tach shows about 2,300 RPM so I'm guessing it's around 1,800 actual.

I haven't done anything (been working) to track down the P0123 code origin nor the intermittent high idle. I can do so in the morning. I have a feeling it's a grounding issue. My throttle body is pretty mucky and I did take it off a couple of weeks ago when I cleaned out the IAC sensor area, also sprayed it with throttle body cleaner but some of that stuff is baked on there for many years. It needs a soaking and thorough cleaning. GM doesn't make them any more so only aftermarket units are available (in larger 52 and 58mm sizes). I'm also figuring it could probably be rebuilt to replace worn parts.

At any rate the car still drives fine. It gets roughly 21mpg on average with very little highway driving. Kinda low maybe or maybe not.

More to come.

GaryDoug

Probably, if they connect to the DLC. Some states do and other's don't.

Not Dave

I just tested the voltage going into the PCM from the dark blue TPS wire. It showed a normal 0.65 V until I moved the wiring harness behind the purge solenoid, at that time it jumped up to 1.7 V. Move the harness around and the voltages moved up and down. Left the harness alone and it goes back to 0.65 V.

My car has a gremlin! Need to start tearing looms apart to see where the issue is. Bummer. It could be a loose ground wire somewhere too. Once I figure that out it may be the end of the high voltage issue. Moving the wire around at the TPS plug did nothing so I know it's somewhere between the sensor plug and the PCM plug. I think.

Looking at Shbox's website for wiring help along with other internet searches. I found from his site that it was the dark blue wire on the gray connector #22.

GaryDoug

Do this: Push a very small pin or needle through the black wire at the TPS cable and use a wire to ground it to the engine somewhere. See if the problem with the voltage shifting when you move the harness goes away. If it does, you are looking for a broken black (ground )wire to the pcm signal ground for the TPS.
When done, seal the punctures with some clear lacquer or nail polish or...

Not Dave

That's a good idea. I'll do that next time I have the hood up. I buttoned everything back up. Had to get new 1" black wire loom from the auto parts store and some new reflective tape for it over the AIR injection as the old stuff practically fell apart. The loom had sagged down to touch the AIR check valve and the silver tape was partially burned through. The loom wasn't damaged and neither were the wires that I could see.

Not Dave

I ended up going back out to the garage and found out it was indeed a bad ground. I temporarily have a new ground wire grafted in and test drove it. No more high voltage or engine surge. Not sure where the bad portion is but glad to have figured out that's the problem. If all goes well it's off to get inspected then registered tomorrow. Thanks guys!

EDIT: Just got back from driving it about 25 miles. No SES light though two codes did come up. P0123 as it was in there from before the fix and the one for EVAP Purge Solenoid. Well, that EVAP thing came up because I failed to reconnect it yesterday and drove around with it like that. Spotted it today and reconnected it. DOH!! The codes have been cleared and the car should be good to go.

Tapatalk on a Note 2.

Not Dave

Passed inspection! No codes thrown! Now to pay the state several hundred dollars for registration.

Tapatalk on a Note 2.

Black93lt1

Gary is this the other thread you were talking about with the tps problem....i show code 22 which I believe is code p0122