(Solved) Replaced TPS and connector, still getting P0122
 

I've replaced the TPS multiple times and just replaced the connector and I still get a P0122. Please help. This is causing a really harsh 1-2 shift. I can delete the code and when I start driving again it'll shift fine and then a minute or two later the code comes back on and the shifts start getting harsh. I've also left the battery unplugged to try to reset the PCM.

Have you checked the voltage at 0% . Should be around .065 volts

Here's the voltages

Grey 5.03 volts
Blue 0.6 volts (closed) 4.5 volts (WOT)
Black 0.033 volts

Edit: meant .65 v in post #2

Wiring stuff from my Hayne's manual. Admittedly, my experience with electrical stuff is more limited to splicing wires and replacing ceiling fans, light sockets, etc rather than troubleshooting more complex issues.

Some things I noted,

-the TPS ground splices into the engine coolant temp sensor ground, which goes to black 2

-grey from TPS goes to grey 17

-blue from TPS goes to blue 12

-the TPS is mentioned on the page prior (see pictured) with blue going to blue 31



https://cimg1.ibsrv.net/gimg/ls1tech...fde79d47cd.jpg

https://cimg3.ibsrv.net/gimg/ls1tech...7a3907f0ff.jpg

These are junk.

You can now get the GM schematics for free on AutoZone.com. Just register and go to the repair section.

http://repairguide.autozone.com/znet...3f8024bc90.gif


Testing the TPS fully is hard because you have to probe the sensor in real-time, which takes special tools. Getting to the source of you problem should be straight-forward with basic tools. Just unplug the sensor and make sure it's getting 5V at the grey wire. (Test the grey to a body ground and the black ground.)

Its also not unheard of for TPS sensors to be bad out of the box.

Hi wssix99, I had checked the voltages with the key turned halfway to have power and with the TPS plugged in while checking the voltages through the back of the connector.

Here's the voltages

Grey 5.03 volts
Blue 0.6 volts (closed) 4.5 volts (WOT)
Black 0.033 volts


You said to check the voltage with the sensor unplugged and measure the voltage coming from the grey connector wire. Is that different from what I did with the sensor still plugged in? If so, I'll test it unplugged and report back.

I've been using this webpage to troubleshoot and it seemed like a reasonably thorough resource.
https://www.troublecodes.net/pcodes/p0122/

I've gotten halfway through it (the results I posted) before the weather started getting a little unwieldy. Here's the next section that says it's for checking the wiring itself, testing that the power is about at battery voltage and testing for continuity between the sensor and PCM via ohms.

"Test the TPS circuit wiring
If the TPS checks out OK, but you still have P0122 code illuminated, you’ll need to check the sensor circuit. First, you want to disconnect the sensor connector and test for power and ground. You can do this using a digital multimeter.

Start by consulting the repair information for your vehicle to determine which pin on the connector is power and which is ground. Next, set your multimeter to the volts setting. Touching the black multimeter lead to ground and the other to the power feed on the connector, you should see a reading that’s close to battery voltage. If not, you have a problem with the sensor power supply. You’ll need to consult the power side of the wiring diagram to find where the circuit fault lies.

To test the ground side of the circuit, connect the red multimeter lead to the battery positive terminal and the black lead to ground. Once again, you should see a reading of about 12 volts. If not, you’ll need to consult the ground side of the wiring diagram to find where the circuit fault lies.

If everything is OK up to this point, you’ll want to check the TPS signal wiring to the PCM. Using a digital multimeter set to the ohms, connect one side of the meter to the harness side of the TPS connector and the other to the TPS input pin on the PCM. This tests for continuity between the sensor and PCM. If your meter reads OL, there is an open somewhere in the circuit that must be repaired. If not, the PCM is likely the problem and should be replaced. However, PCMs rarely go bad, so make sure you double check all of your work before condemning the PCM."

Here's the specific diagram for my vehicle from Autozone

https://cimg4.ibsrv.net/gimg/ls1tech...94c837f916.png

Unplugged connector test results

A) Multimeter black lead to ground, red lead to blue wire 0.08 volts

B) Multimeter black lead to ground, red lead to grey wire 5 volts

C) Multimeter red lead to positive on battery, black lead to black wire 12 volts



According to the connector testing procedure I posted above, test (A) should read 12 volts but I'm getting 0.08 volts, so would this suggest I have a frayed blue wire somewhere along its length?

Yes, this gives you an idea if your car's wiring is good; taking the sensor out of the equation.


This doesn't tell you anything because power can back-feed from the PCM and other circuits.


This is good power to the sensor.


This is a good ground.


I would test your red lead to the grey wire and black lead to the black wire; just to be sure everything is tight. You should get 5V. If so, the next thing to check is your sensor. I recall its a variable resistor, so it should test with the ohms function on your multi-meter. (I expect you should be able to find an instructive YouTube video on this. I like the ones put out by Wells.)

Testing read lead to grey wire and black lead to black wire is 5 volts on the nose.

Here's a video of the voltage going from closed to WOT (sensor connected, measuring through the back of connector). There's a weird thing it always does only when going up, is right at 2 volts it'll say OL but not when going down. The previous new one also did this. But the voltage movement is always smooth so I had been ignoring it.

Testing one of the sensors by itself using ohms shows closed about 0.5 to 4.8 turned completely. It'll do OL at 2 ohms and periodically do OL randomly.

What are the odds that three new ACDelco sensors would all be bad? Maybe I should try another brand and see what the results are.

It looks good. Do you have leads that would allow you to test the pins on the PCM and test the voltages there? (You could have a wiring problem between the sensor and the PCM.) ^ That's also the next step in the OBD code procedure.

You may also scan threads on TPS. You may find some other ideas. I'm not saying this thread will have any gems for you, but it shows that this circuit can be a PITA: https://ls1tech.com/forums/general-m...-up-again.html

I'll have to read up on testing the PCM. I'm not even sure where it's located.

That's not "right". It could be the sensor, or one of your contacts loosing its connection to the lead you are probing.

If it is the sensor, it could be the source of your code.

There are contacts that travel around a circular "track" of metal inside the sensor and if those two loose their connection, the circuit (and voltage) will cut out for a second.

Does this happen 100% of the time, always at the same place of motion?

It was always at 2 volts hooked up, or 2 ohms with the sensor disconnected and testing for resistance. On every sensor I tested.

Here's the thing, I brought a couple of the sensors into my lab to our engineer equipment fix guy and disassembled them, or rather, took the metal circle cover off. Didn't see anything that stood out but cleaned the track with an air canister and ethanol. Reassembled them and hooked them up to my multimeter. Same OL error at the same point. However, he was able to get it to travel without producing an error by holding it rigidly. He was also using his Fluke multimeter, as opposed to my $25 one.

I'm going to hook the sensor he got to work right up to my truck and redo the readings using his Fluke multimeter and report back.

I really appreciate your help, wssix99. I'm in the middle of writing my dissertation and this is not something I need to deal with right now. I'm hoping it's a crappy sensor quality issue and not a deeper electrical issue. I found the PCM but if I find a wire short that would be a huge PITA to unravel it from the main wire bundle and feed a new one through.

This is a particularly difficult sensor to test. Some codes (not yours) can only be probed with the sensor fully installed.

When you disassembled it, did you find a spring inside? I recall one other thread mentioning that a member got a batch that was missing that part. As you found, the contacts maintaining contact is key. If they separate, then you'll get that low voltage condition.

Probing the PCM is a pain. I recall some members have had a short in that wire and had to pull the harness apart to find the break. (That kind of break/short doesn't happen on its own - it happens usually during other work on the engine.)

This part is a slip ring: http://www.moog.com/products/slip-ri...lip-rings.html

Some slip rings are cheap sh&!. (Like the one in the TPS sensor.) Some are higher quality, like the one in our steering column (commonly called "the clockspring"; I think its a slip ring and not actually a clockspring) that feeds power to the steering wheel airbag. I used to study near a factory that produced the slip rings that handled all the electrical for tank turrets. Cool stuff - too bad we don't have a better one in the TPS...

Good luck with your dissertation. Are you kidding when you say that you are working on it now? Most of the writing happens two weeks before the draft is turned in, right? ;)

Well, the nightmare seems to be over. One of the new sensors that wasn't working right that we opened up, fiddled with and cleaned the track with ethanol and an air can, and the Fluke showed a smooth, no error voltage increase and decrease, was reinstalled and the code went away yesterday evening and as of now, with probably close to two hours of driving everything seems fine.

I also pressed the connector female ends more closed to ensure the best possible contacts.

Not sure what specifically fixed the sensor issue but I won't look a gift horse in the mouth.


One thing I did remember is that I have a BAFX real time OBDII scanner that bluetooths to my smartphone and can monitor the PCM's TPS data in real time. One of the sensors that seemed to check out, voltage-wise, a few days ago didn't show any TPS data in the PCM. But the sensor that worked yesterday shows smooth changes in the TPS data while driving.

Thank you, wssix99.


And ACDelco, up the specs and QC for whatever factory makes your throttle position sensors.

For LS1 Tps idle voltage should be 0.47-0.55 volts and no more than 4.69 at WOT. otherwise you'll be getting the P0122.

There is another thing to watch out for here, also. The serial bus for the OBDII connection is so slow that it can look like the TPS is zeroing out.

I had a good sensor that was showing bad on my real-time scanner because the scanner and PC were faster than the OBDII was sampling/reporting the data.

Measuring the signals directly at the sensor (like you did here) is much more trustworthy.