I've got a code 21 on my 84 Vette and am trying to check the TPS. I'm measuring the voltage between the A and B terminals as suggested with the ignition on but engine off, I'm getting 4.85 volts at closed throttle and then 5.09 volts at wide open throttle, nowhere near the .525 volts it's supposed to be. It does change voltage when I move the throttle but I'm confused by the voltage.

Any suggestion/guidance appreciated.

 

...some TPS are movable, while others are fixed. set while engine is running across A&B to a value of .54 volts +/- .7 for either type. for fixed version it is possible to delicately oblong the holes with a file to achieve the same results..check tech note stuff in my signature

 

You could pull it off and just check the resistance. It's just a variable resistor. I'm not sure how much it should vary for that model. The voltage and resistance changes are proportional.

It should change slowly as you vary the position. If it jumps around, something is up. It's been said an analog meter is better for this, as digitals change more slowly.

I'm not sure how the fixed versions work.

 

Did this just start all of a sudden or had you done some work on the engine just before it started?

I'm not familar with the 84 setup because it's different than the later years, but for my 86, Code 21 (TPS High Voltage) will set if the ECM reads voltage higher than 4.5 volts with the either the ignition "ON" or the engine running, or engine running and more than 2.5 volts for more than 3 seconds with only a small amount of air flow (forgot the exact #) measured in Grams per Second.

So if yours is the same or similar, you've got high voltage readings on both ends of the spectrum. All I can suggest is for you to loosen the little bolts/screws that attach the TPS and rotate the connector end downward. This (at least on the TPI engines) will lower the voltage.

You may be able to bring things back into proper range doing that. Then clear the stored error code by disconnecting the battery for 30 seconds, start the engine and see if the code returns.

If the code returns (or if you're unable to lower the voltage readings,) check the TPS readings again and if they're back up there showing high voltage readings, you may need a new TPS.

One other check you can run is to clear the code, then disconnect the TPS. Start the engine and let it idle for about 1 minute or until you get a SES light. Then shut down the engine and pull the code from the ALDL.

If you pulled Code 21 there's a short on TPS wire 'B', either shorted to voltage or shorted to 'C' (both of those are TPS wires)

If you pulled Code 22 you need to use a test light on TPS wire 'A' to get a 12 volt reading

If the test light comes 'ON' you've got a faulty TPS connection or TPS sensor

If the test light is 'OFF' you've got an open circuit on TPS 'A'.

When you wrote "A and B", you are using the top and middle wires on the TPS, right? Top being 'A' and middle being 'B' and 'C' is the lowest one.

Those are the ones I use for checking; top and middle and the ones I'm referring to above.

I'm kind of shooting in the dark on this one because I don't know how much your system differs from mine and how your TPS is actually mounted.

Hope this helps, though

Jake

 

I just adjusted my 84 and i used the bottom 2 wires, worked fine, no problem.

 

On the 85 and up TPI, the bottom wire is a 5 volt reference voltage that isn't used to check/set the TPS voltage. So I see that the 84 is different.

Like I said, I'm shooting in the dark on this one. Hopefully some other guys with 84 knowledge will post and help you with your problem.

Jake