Code 22 - TPS voltage low.... but I think the TPS sensor is good (Page 1/2)
McCool JUL 18, 02:15 PM
Okay so here's what's going on...

The idle on my 2.8 is very irratic, it bounces between 1000-2000. It throws code 22.

I checked the voltage at the ECM. I'm supposed to be getting approx. .5 volts at idle and around 4.5v at WOT. I'm obviously getting nowhere near that, hence the code 22.

I have 5 volts between the grey wire and the black ground wire.

I cleared the ECM codes and jumpered the grey wire to the blue wire on the TPS to send 5 volts to the ECM to verify that there were no problems with the wiring, I saw the 5v between the blue and ground at the ecm, i let the car run with those wires jumpered till it threw a code 21. The service manual says that means the wiring and ecm are good and the TPS is the problem. With the TPS sensor disconnected and the blue and grey wires shorted, the idle is MUCH better, Indicating to me that the injectors are okay and that the TPS sensor is the problem

Here's the wierd part. As far as I can understand, the TPS senskr is just and potentiometer.... When I put an ohmmeter across the blue wire and the tps ground wire at the ECM, I can see a smooth transition between around 1400 at idle up to 5500 ohms at WOT. Which to me means that's the TPS sensor is good providing that those value are the proper ones for the TPS

So first question, can anyone confirm the resistance values for the TPS sensor? And question two, is measuring the resistance values of the TPS sensor a good way to diagnose whether the sensor is functioning properly or not?
fierosound JUL 18, 02:46 PM

quote
Originally posted by McCool:

So first question, can anyone confirm the resistance values for the TPS sensor?
And question two, is measuring the resistance values of the TPS sensor a good way to diagnose whether the sensor is functioning properly or not?



The Factory Service Manual - Section 6 Driveability & Emissions - Fuel Injection
Pages 6E3-A-42, 43 has a diagnostic flow chart showing only expected voltages to determine good/bad TPS sensor.

If NOT the TPS itself, could be a short or open circuit, even a faulty ECM.

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McCool JUL 18, 06:12 PM

quote
Originally posted by fierosound:
Pages 6E3-A-42, 43 has a diagnostic flow chart showing only expected voltages to determine good/bad TPS sensor.



I am not getting the correct voltages, I get .01v at idle and .06v at WOT hence the code 22. But the fact that I can read TPS resistances at the ECM would Indicate to me that the TPS is fine provided the ohmic value is supposed to be between 1400 and 5500 ohms.

I dont think the ECM is to blame because as I said before, I removed the TPS harness, jumpered across the 5 volt grey and the blue wire and the idle conditions changed entirely and the ECM threw code 21 for TPS voltage too high, which is exactly what it should do.
theogre JUL 18, 07:19 PM
1 wire is 5v
1 wire is ground.
Check them before checking other things.

then read volts to frame on signal wire. Back probe it while connected to sensor.
then do same but at ECM plug.

Even If you have a good sensor...
Sensor Socket maybe be bad or dirty. Can easily clean/fix Weather pack plugs but need a tool or can easily wreck them. if later car w/ metripak 150 PTS, is different the Weather Pack type and harder to clean them.
Wire(s) to ECM can be crap
ECM may have problems w/ its sockets or anywhere inside.

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fierogt28 JUL 18, 07:23 PM
Replace the TPS, its only a 100$ part. Replace with AC Delco for best results.

On my 88GT, I replaced the TPS and IAC , cleaned the throttle body and adjusted the throttle adjustment screw to the throttle plate opening.
But if yours has a cap over it, don't touch it ! Its already set. Its just because someone fooled around with my TB before I did. (the cap was already off)
These cars are over 30 years old...parts don't last forever.

A bad ECM would set code 55. If your wiring is tested good, its the sensor.

Be sure, and check manually...the battery connections and grounds. Don't assume, look carefully.
Sometimes problems are stupid overlooked problems. Been there.

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88 GT, Loaded, 5-speed.
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fierosound JUL 18, 07:49 PM

quote
Originally posted by McCool:

I am not getting the correct voltages, I get .01v at idle and .06v at WOT hence the code 22.
But the fact that I can read TPS resistances at the ECM would Indicate to me that the TPS is fine provided the ohmic value is supposed to be between 1400 and 5500 ohms.




The ECM tells you there's a problem with the TPS.
The voltages you get when testing tell you there's a problem with the TPS.

Reading 0 ohms would mean it's dead.
Getting the readings you are getting does not mean it's any good though.

See advice from other guys above...
McCool JUL 18, 08:15 PM

quote
Originally posted by theogre:

Sensor Socket maybe be bad or dirty. Can easily clean/fix Weather pack plugs but need a tool or can easily wreck them. if later car w/ metripak 150 PTS, is different the Weather Pack type and harder to clean them.





I'm actually leaning towards the weather pack/sensor socket connection honestly. I already called around and no one seems to stock replacement weather packs, even the GM dealership said there wasn't a hope in hell that they would have a replacement connector. I may have to order a set online. In the mean time I think I am going to try to rig up a solid connection without using the weatherpack because I really think that the TPS is functioning properly and the problem is elsewhere.

Can anyone confirm that the TPS is just a potentiometer and does anyone know what the resistive values of the TPS are supposed to be?
Patrick JUL 18, 08:54 PM

Google and YouTube are your friends.

theogre JUL 18, 11:52 PM
Weather Pack parts are still common and available.
You can reuse an extinct shell w/ new connects because All Weather pack shell uses same pins inside. Shells don't even care if pins are male/female in them. The only part different is for bigger/smaller size wires... wire seal and crimp part is made to take them. Most are green seals w/ matching pins for use w/ 20-18ga wire.

if you can't or don't want to make terminals, get a generic pig tail "kit" w/ right terminals from Dorman etc and use them in you old shells and splice the wires.

I don't know which pins (male/female) you need for TPS. Go to AZ etc and look in Dorman Help! and Conduct=tite to start. or www.dormanproducts.com amazon etc
McCool JUL 25, 11:38 PM
I took my TPS apart to confirm a few things because no one has the answer for the question I have.

So in order to help the next guy out here is an easy way to diagnose if the TPS itself is working.

The TPS has three wires running to it:

The Gray wire (5V Reference) connects to pin A on the TPS
The Blue wire (TPS signal) connects to pin B on the TPS
The Black wire (Ground) connects to pin C on the TPS

The TPS is a simple three pin potentiometer, nothing fancy about it. A functioning TPS will read approximately the following resistive values:
Across A and B - 5000 ohms at closed throttle with a smooth transition to 1000 ohms at WOT
Across A and C - 4200 ohms at all times
Across B and C - 1000 ohms at closed throttle with a smooth transition to 5000 ohms at WOT

If your TPS reads close to these values then it is functioning correctly and the code 22 is due to a bad connection or an ECM problem.