Throttle control codes wont clear, even though named parts replaced.

Asked by Guru94N8NQ Sep 17, 2020 at 07:14 AM about the 2009 Buick LaCrosse CXL FWD

Question type: Maintenance & Repair

2009 Buick Lacrosse, 3.8 liter 6 cylinder

Approx 2 years ago, new MAF and Throttle body with TPS.

2 weeks ago the check engine light came on with "Reduced Engine Power".
Codes as follows:

P0068, Map, maf throttle position correlation,

P0102,Mass or Volume Air Flow A circuit low,

P1125, Accelerator Pedal Position System,

P2120, Throttle/ Pedal Position Sensor/ Switch D Circuit

P2138, Throttle/ Pedal Position Sensor/ Switch D/E Voltage Correlation

Since MAF and TB/sensor fairly new, I replaced the pedal.

Cleared codes. Last 3 came back (no MAF codes). Checked all connectors for
moisture and wire integrity. Did find some moisture in the multi connector (the
one mentioned in a service bulletin), dried it out and used electrolytic grease.

Tried to check voltage on TPS, but it has a 17 pin connector. Could not find a 5
volt input to the TPS. I found a 12 volt and a few under 5v (3.6v was strongest
under 5).

Cleaned up Throttle body and recalibrated TPS.

Cleared codes, they stayed off while i test drove (approx 3 miles) and same
codes returned with reduced engine power. Codes wont clear and R.E.P. light
stays on.

Live data indicates a discrepancy in my APPS voltages, but its a new pedal.

Ive tried to recalibrate the TPS again but it didnt change anything.

I cannot locate accurate info on the 17 pin connector.

At $200 for a new TB/TPS and new pedal installed, i dont want to spend it if its
not going to fix the problem.

How can i trace out this gremlin? Where might i locate good wiring info on these
sensors? How can i OHM out the sensors to determine if they are working?
Would a diag comp scan accurately locate it and could it differentiate between
bad sensors or /and ECU that needs to be replaced or reflashed.

Truth is that this is still a nice car and i couldnt replace it for the several hundred
this might cost. I dont mind spending the money, but i dont want to just
randomly swap out parts without knowing that its going to solve the issue.

Any help getting me in the right direction would be appreciated.

Dale

40,015

beatupchevy answered 4 years ago

I think you need a competent technician , other things can go wrong while trouble shooting another problem by pure coincidence . If you really don't understand the circuits then you're just guessing . I remember someone had one of those and they had a code problem , the mechanic ran it all day trying to figure it out but could not .

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Guru94N8NQ answered 4 years ago

Thanks buc. If i cant get the detailed info im looking for, ill end up having to do that. Im pretty good under the hood most of the time, but this one just keeps giving somewhat random codes. Some of my electrical readings dont jive with memory so im looking for pretty specific info to check before going that route. Dale

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Throttle control codes wont clear, even though named parts replaced.

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Throttle control codes wont clear, even though named parts replaced.

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