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Engine codes P0122 and P1406

Tiny
SMITHSONSAUTO
  • MEMBER
  • 1994 CHEVROLET S-10
  • 4.3L
  • V6
  • 4WD
  • AUTOMATIC
  • 60,000 MILES
These two codes keep coming back. I replaced TPS and IAC no fix. I replaced EGR no fix. New ECM fixed for a few days then came back. I was told by fellow tech to change main speed sensor which made sense because it was shifting odd, so I changed it fixed issue for about a month. Now it is back again. I am a tech and have followed to the letter all flow charts and done everything. I truly believe I am on the right track with speed sensor. Maybe exciter ring in transmission that speed sensor reads off? Do I need to re-flash computer again? I am really scratching my head here.
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Thursday, October 4th, 2018 AT 4:34 PM

13 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning

What is the exact issue you have?

1994 cannot be reflashed. Are you sure you gave us the correct information? 122 and 1406 are for OBD 2 and the information you gave us is an OBD 1 system.

Roy
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Friday, October 5th, 2018 AT 3:31 AM
Tiny
SMITHSONSAUTO
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  • 9 POSTS
My bad 1996. I am working heads on a 1994 the s10 is a 1996, OBD2.
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Friday, October 5th, 2018 AT 7:16 AM
Tiny
SMITHSONSAUTO
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  • 9 POSTS
The exact issue is a p0122 TPS circuit low voltage keeps popping. The engine idle all over the place, shifts really hard, idle sometimes to 2,800 rpm. Had to shut down the EGR code 1406 pintle pos. Circuit I believe is secondary to TPS trying to fix first even though I tried a new EGR valve all circuits, signal voltages and references were good.
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Friday, October 5th, 2018 AT 7:26 AM
Tiny
SMITHSONSAUTO
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  • 9 POSTS
These two codes are all that are present and come together to the party like a couple. And by the way Good Morning to you too.
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Friday, October 5th, 2018 AT 7:36 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
LOL. I hear you.

What is the TPS voltage at idle? It should be.5 to.75 volts. Make sure it rises smoothly up to 4.8 volts with the throttle open.

This will affect how the transmission shifts as well.

Roy
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Friday, October 5th, 2018 AT 8:09 AM
Tiny
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  • 9 POSTS
Voltage is right on.48.5____4.8. But when disconnecting TPS and jumping signal wire and reference wire voltage was almost 5 volts that is why I replaced the VCM. Just wondering if I should use genuine GM parts instead of Napa.
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Friday, October 5th, 2018 AT 8:43 AM
Tiny
ASEMASTER6371
  • MECHANIC
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No, that is correct. It is a 5 volt reference voltage. You just jumped it and it should be 5 volts because it has no load.

With the TPS connected, it only goes to 4.8.

Roy
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Friday, October 5th, 2018 AT 9:26 AM
Tiny
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Correct, but on flow chart it says disconnect TP sensor plug and jump with wire sensor signal and 5 volt circuits if greater than 4 volts replace VCM.
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Friday, October 5th, 2018 AT 11:29 AM
Tiny
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You know I am sitting here thinking of what you said, feeling a little stupid now I am at a loss totally just going to start over start with EGR issue and then go back to the TPS.
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Friday, October 5th, 2018 AT 11:45 AM
Tiny
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If sensor is unplugged there would not be a losd but like I said I am starting over.
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Friday, October 5th, 2018 AT 12:17 PM
Tiny
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Okay, let me know if you have any other questions.

Roy
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Friday, October 5th, 2018 AT 1:06 PM
Tiny
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I appreciate your time.
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Friday, October 5th, 2018 AT 2:26 PM
Tiny
ASEMASTER6371
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Never a problem.

Always glad to help.

Roy
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Friday, October 5th, 2018 AT 2:44 PM

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