Throttle Position Sensor (TPS) Problem

[Landru]

I have a 1994 Park Avenue. I had a code P0122—low TPS voltage. The scanner showed a sensor output of 0.19V and 0% throttle angle at idle. WOT was 1.68V and 44% throttle angle. I checked the connections and they were OK. I jumpered the 416 and 417 circuits and got the expected 5 volts on the scanner. So, I concluded that I needed a new TPS. I installed a new one and got 0.25V at idle and about 4V (I did not write down the exact reading) and 99% throttle angle at WOT. So, I figured I had fixed the problem.

On the first drive, after about 15 minutes (about when the car would have been fully warmed up?), the SES light came on again. I stopped and scanned. Initially something like 0.17V at idle and low readings at WOT. I left the scanner on while driving home and observed what appeared to be a gradual decay in the idle reading to about 0.09V. WOT is 1.9V and 40% throttle angle. The car seems a little underpowered but is running OK. (Which is a tribute to the GM engineers and the redundancy they built into the control systems.)

I guess my caveman repair attempt succeeded in frying a $70 TPS. The new one I installed was a Borg-Warner EC3046—which the auto parts guy said was equivalent to the ACDelco 213-915. Maybe my mistake was not sticking with ACDelco. Seems like the TPS is located in a tough thermal environment—so near the coolant line and exhaust manifold. Maybe I was unlucky and got a weak part. Or maybe I have a bigger electrical problem that’s affecting the TPS. Any ideas or guidance would be appreciated.

[Bronco2]

After the car warms up do still have the 5 volts going into the TPS from the ECM? Need to check with multimeter. I doubt you fried the new TPS just by installing it.A defective new part is always possible,but its strange that you are grtting the same readings.

[Landru]

I am getting 5V from the ECM (gray wire) on a multimeter with the engine cold and warm.

[Bronco2]

Check the output wire on the TPS and see if that reading agrees with what your scanner is saying.If they are the same I would think a bad/binding TPS.If the readings look normal on the meter but not on the scanner pull the ECM ,leave it hooked up,back probe the TPS wire and compare readings there.Out of town tomorrow,will check back Mon. pm

[RABarrett]

Good diagnostics Bronco. You did, however, miss one thing, simple, but important. The problem must be checked when the light is on, when the ECM is warm. Make sure the ECM reading and the multimeter readings agree when the problem occurs. Otherwise, good show! Ray

[Landru]

Thanks for the responses. You helped me to fix it, although directly. While making the direct checks with the voltmeter, I noticed a pinhole leak in the thermostat cover gasket that was venting coolant vapor. Looking closer, I found moisture inside the connector on the TPS, though I don't know how it made it through the "Weather Pack." I "baked" the TPS by resting my shop light over it for a while in the hope of drying out the TPS. I guess the moisture was getting to the potentiometer (however that works) and causing the malfunction because now I get 0.27V TPS output on the meter at idle and other nominal readings. The code has cleared--hopefully for good. Now to change the thermostat gasket and probably the throttle body gasket as well because it also appears to be leaking. This car has 120K miles and sat for six months so I guess I will get to enjoy gasket problems for a while. Thanks again for the replies!

[Bronco2]

To Landru-your welcome.I like electrical/diagnostics problems.Its hard to do online but the problem was found. To RA Barrett-no offence meant-if you check the previous posts I asked about the warm/cold thing.Sensor outputs can degrade and cause problems well before a 94 system will turn on the lite. Also,before your comment about what I missed,I noticed that none of the 126000 members of this forum bothered replying.

[RABarrett]

It is interesting that so many people will advise regarding what should have been checked, but have no clue regarding the assistance during the problem. Also, kudos to you for being one of the few individuals with a clue regarding how the system works. Again, good show! Ray