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Paul M ASE Master
Paul M ASE Master, ASE Master Tech
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What do you check/replace for a P1639 code (5 volt reference

Resolved Question:

What do you check/replace for a P1639 code (5 volt reference 2 circuit)?
Submitted: 6 years ago.
Category: Chevy
Expert:  Paul M ASE Master replied 6 years ago.

Hello and thank you for using Just Answer


this is most commonly caused by the AC pressure sensor or the Fuel Tank Pressure sensor


click here for the testing information


let me know what you find and if you need more help



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