ascastil

Well I got a code po123. Measured voltage at tps and throttle closed its .8, WOT its 4.75. I know the .8 is a little high but wot seems to be in specs. I could adjust for the .8 if thats the problem, but I thought the code is for wot voltage.

Just installed new iac valve, new tb gasket, new injectors, new fuel pump, pcmforless reflash.

I dont have access to monitor any readings from the car, just a handy multimeter.

ascastil

Tested the gray wire for 5 volts, it read 6.75, is this good or bad?

Injuneer

Too high. That's the reference voltage supplied by the PCM.

The code sets when the PCM detects more than 4.9V on the signal wire.

ascastil

I was reading a writeup on testing it from a link I got here.
http://www.mainstreamtopics.com/foru...sweep-testing/.
After reading it again, maybe the instructions arent so clear. Now originally, WOT was 4.75v between the blue and black wire. Then
I read that and I tested the gray wire straight to ground and got 6.75v. Let me know what I need to do. Sorry about the confusion.

ascastil

So the gray reference wire and the blue signal wire both need to be below 4.9v?

MikeGyver

Check your meters battery.

ascastil

I swapped out batteries in my meter and double check readings in a bit. Car is getting exhaust work.

Injuneer

No. The PCM supplies 5.0V reference between the gray and the black wires. It has to be close to 5.0, or the signal voltage will be corrupt.

The signal voltage, measured between the blue and the black wire, is what the PCM checks. If the signal voltage is over 4.90V the code sets. If you have 4.75V WOT, it would be odd to find 6.75V on the reference side. The signal pulls down the reference voltage, based on the variable resistance of the rheostat that rotates with the throttle shaft.

My point in telling you that the code is based ONLY on the 4.90V value, was to let you know that 0.80V at closed throttle is not what set the code.

ascastil

Ok cool thanks for the input Injuneer. Anyways, the story has taken a turn. On my way back from getting exhaust done with no codes present, decided to go WOT. CEL came on, when I scanned it it was po122 and 123, low and high voltage. I havent gone out and checked any wires for power yet, but will when it gets cooler.

This is what I'll try in a bit, correct me if I should check other things too.
1. Check for 5V reference between gray and black wires.
2.Check to make sure voltage doesnt pass 4.9V between blue and black wires, WOT.
3. Check voltage with throttle closed between blue and black wires.

Injuneer

P0122 sets when the TPS voltage drops below 0.20V. Sounds like you may have a loose wire or damaged harness connector.

To check the signal voltage:

-key on, engine off, closed throttle, check the voltage between the blue and black wires. Should be in the range of 0.20 - 0.90V. The PCM reads that voltage when you start the engine, and sets that as the baseline (0%) throttle position.

-start to open the throttle blades SLOWLY. Watch the voltage. Should increase smoothly, with no spikes or dropouts, until it reaches about 4.00V above the closed throttle voltage when the blades are fully opened.

ascastil

OK, results are in.

Throttle blades closed, key on, engine off, voltage was .742 between blue and black wires.

Opening throttle slowly, voltage increased smoothly by .2 volts at a time till WOT which was 4.67 volts.

I noticed in my first post the throttle closed voltage I measured yesterday was .8, is the change in .8 yesterday till .742 today normal?

Injuneer

Are you sure it was fully closed both times? If there's any dirt in the throttle body, or the linkage is sticky, the blades may close in a different position.

You are also going to get different results if the reference voltage (gray to black wires) changes, and it shouldn't be changing. If its changing, and going significantly above 5.0V it may be a voltage regulation problem in the PCM. Check the reference voltage to the MAP sensor (gray to black wires) and see if that is where it should be.

ascastil

Gray to black wires is 4.97V. Ill pull the intake elbow tomorrow and clean the throttle body.

Injuneer

Now the reference voltage sounds right.

ascastil

Hmmmmmm... reference voltage is good, closed throttle voltage is good, WOT voltage is good, voltage is smooth during throttle blades opening. What the heck could this be?