Code 21 TPS voltage high?

Tiny
GILBRO
  • MEMBER
  • 1990 CHEVROLET CHEYENNE
  • V8
  • 2WD
  • MANUAL
  • 170,000 MILES
Getting one code 21 TPS voltage high. Tested the TPS with voltmeter across blue and black wire and with ignition on throttle closed got like 4.6. I then gradually opened the throttle and the numbers were coming down. Is this a bad TPS because I just replaced it like 2 weeks ago. Any and all help would be appreciated.
Friday, September 29th, 2023 AT 7:59 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,068 POSTS
Hi,

With the throttle closed, it shouldn't be over 2.5v. We may have a short to power or the new part has failed. I have seen a lot of aftermarket parts either not work at all, or they fail after a short time.

I attached the diagnostics below for this code. Take a look at them and let me know if you are comfortable performing them.

Let me know what you find.

Joe'

See pics below. Just a note: With the throttle closed, you should be at approximately 70v.
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Friday, September 29th, 2023 AT 10:56 PM
Tiny
GILBRO
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  • 12 POSTS
Does scan mean measure? Because I don't have a scanner but I do have a voltmeter. Just want to make sure so I'm not wasting anyone's time.
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Sunday, October 1st, 2023 AT 1:38 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,068 POSTS
Hi,

That means a scanner is used. If you have a multimeter/voltmeter, check the gray wire first for a 5v reference signal. The dark blue wire is the signal return, so that is the one that should be near 0v when the throttle is closed.

When you check for the 5v reference, you can have the connector disconnected. When you check for the TPS signal, it needs to be connected and you need to back probe the dark blue wire.

Let me know what you find.

Take care,

Joe
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Sunday, October 1st, 2023 AT 7:58 PM
Tiny
GILBRO
  • MEMBER
  • 12 POSTS
With the ign on not running I got 5.04 volts on gray wire back probed blue wire n got 4.17 with throttle closed. I slowly opened the throttle and the numbers decreased to 0.3. I also checked for continuity on ground wire back to battery and there is.
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Sunday, October 1st, 2023 AT 9:47 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,068 POSTS
Hi,

That sounds like it is working backward. Is the TPS still under warranty? If it is, I would switch it out and see if that changes things. Something isn't making sense. LOL

Let me know.

Joe
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Sunday, October 1st, 2023 AT 10:20 PM
Tiny
GILBRO
  • MEMBER
  • 12 POSTS
I had wires hooked up wrong. Thanks for your time and knowledge. Much appreciated.
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Wednesday, October 4th, 2023 AT 8:18 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,068 POSTS
Hi,

Thanks for the update. That explains why it seemed to be working in reverse. LOL However, that is a very easy mistake to make.

Regardless, I'm glad to know you got it fixed and it's working properly again.

Take care of yourself and feel free to come back anytime in the future.

Joe
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Thursday, October 5th, 2023 AT 5:19 PM

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