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20008 Silverado p0121 now 0507
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comnavguy
User
Jul 17, 2015, 8:06 PM
Post #1 of 7
(3901 views)
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20008 Silverado p0121 now 0507
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This is a 2008 Silverado with V8 5.4 L 128,667 miles. It failed inspection because of code 0121 Throttle Position Sensor. Replaced the sensor and now it is showing code 0507 idle out of specs and it idles up to 2500 RPM in neutral and park but once in gear drops back to normal with or without A/C on.
The book says that the idle air control valve is in the throttle body. We replaced the throtle body, and we still have the same problem.
Help. Help. Inspection is due.
(This post was edited by comnavguy on Jul 17, 2015, 8:34 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Jul 18, 2015, 6:10 AM
Post #2 of 7
(3884 views)
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Re: 20008 Silverado p0121 now 0507
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This has electronic throttle control. The throttle plate is opened and closed by a servo motor that the PCM controls which allows the PCM to control the idle speed.
Did you test the TPS before you changed it or are you a parts swapper? The P0121 doesn't necessarily mean the TPS is the fault. It is a TPS performance code that basically means the throttle position didn't correspond with the expected engine load and throttle position for more than a second. A MAP or engine performance issue could cause that code to appear.
Now you have another issue that you could have created. You need to look at TPS data to see if the PCM is commanding that high idle or if you have something such as a vacuum leak causing that.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 18, 2015, 6:11 AM)
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comnavguy
User
Jul 21, 2015, 3:05 AM
Post #3 of 7
(3845 views)
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Re: 20008 Silverado p0121 now 0507
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A sometimes partsswapper. In this case, yes. I didn't know how to test the part and still don't. MAP is OK and no vacuum leaks.
We did not have the idle problem until we replaced the TPS. The truck was running smoothly. Can you explain that? Why would replacing the TPS cause idle to go haywire?
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Discretesignals
Ultimate Carjunky
/ Moderator
Jul 21, 2015, 4:31 AM
Post #4 of 7
(3840 views)
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Re: 20008 Silverado p0121 now 0507
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Without seeing some scan tool data or even some test data, your guess is good as mine.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Double J
Veteran
/ Moderator
Jul 21, 2015, 11:51 AM
Post #5 of 7
(3830 views)
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Re: 20008 Silverado p0121 now 0507
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Look into this TSB......May help
Subject: SES Light, Idle Surge, and/or Reduced Engine Power Mode with DTCs P0068, P0121, P0506, P0507, P1516, P2101, P2119, and/or P2176 - Clean Throttle Body and Perform Idle Learn Reset
Models: 2007 Buick Rainier
2007-2009 Cadillac CTS-V, Escalade
2008-2009 Chevrolet Colorado
2006-2009 Chevrolet Avalanche, Corvette, Express, Impala, Monte Carlo, Silverado, Suburban, Tahoe, Trail Blazer
2008-2009 GMC Canyon
2006-2009 GMC Envoy, Savana, Sierra, Yukon
2007-2008 Hummer H2
2008-2009 Hummer H3
2007-2008 Pontiac Grand Prix
2008-2009 Pontiac G8
2006-2009 Saab 97x
With a V8 Engine
This PI was superseded to update model years and add information concerning idle surge, reduced engine power mode, and/or DTCs P0068, P0121, P1516, P2101, P2119, and/or P2176 that may be experienced on high mileage vehicles. Please discard PIP4578.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI. condition/concern:
As carbon builds up in the throttle body of a high mileage vehicle, the ECM/PCM learns to compensate by increasing the throttle plate angle.
If enough carbon builds up, an idle surge, deceleration surge, tip-in hesitation, reduced engine power mode, and/or DTCs P0068, P0121, P1516, P2101, P2119, and/or P2176 may be experienced on high mileage vehicles.
If the throttle body is cleaned without performing an "idle learn reset/reset idle learn" with the Tech 2, the ECM/PCM may continue to compensate for previous carbon build up, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or *** * >> >>>P0507.<<<<
In a similar fashion, if the ECM/PCM of a high mileage vehicle is replaced and/or reprogrammed without performing the Throttle/Idle Learn outlined in SI, the ECM/PCM may no longer compensate for existing carbon build up in the throttle body, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or P0507.
Recommendation/Instructions:
If SI diagnosis does not isolate the cause of this concern, inspect the throttle body bore and plate for obvious carbon build up.
If carbon is present, follow the Throttle Body Cleaning Procedure in SI to clean the throttle body.
After ensuring that the throttle body bore and plate are clean, perform an "idle learn reset/reset idle learn" with the Tech 2 and re-evaluate the concern.
Notice: Depending on the vehicle you are working on, the "idle learn reset/reset idle learn" is normally found on the Tech 2 ECM menu for Module Set Up or Special Functions/TAC System.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
(This post was edited by Double J on Jul 21, 2015, 4:38 PM)
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comnavguy
User
Jul 23, 2015, 12:32 AM
Post #6 of 7
(3809 views)
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Re: 20008 Silverado p0121 now 0507
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the idle learn/reset re-learn procedure cured the problem. The TPS sensor was bad.
Thanks for the help guys.
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Discretesignals
Ultimate Carjunky
/ Moderator
Jul 24, 2015, 5:54 PM
Post #7 of 7
(3774 views)
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Re: 20008 Silverado p0121 now 0507
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Good find J!
Glad to read it was a simple case of relearn. Thanks for the follow up  Closed as solved. Can be reopened upon request by the OP.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 24, 2015, 5:55 PM)
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