How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask rpmdiag Your Own Question
rpmdiag, Tech and Instructor
Category: Chevy
Satisfied Customers: 7752
Experience:  Since 1975
Type Your Chevy Question Here...
rpmdiag is online now
A new question is answered every 9 seconds

I have a 1999 Chevy Express 5.7L with DTC code P0102 which

Customer Question

I have a 1999 Chevy Express 5.7L with DTC code P0102 which is MAF sensor low voltage in circuit A I checked the ground an its Ok I checked for 12 volts on the pink wire and its OK I then the yellow cpu reference voltage at the cpu end and I got 4.1 volts I checked the HZ value at the other end and got a reading of 131 which went lower when i reved the engine does this suggest a problem with the CPU should it have a full 5 volts reference voltage?
Submitted: 8 months ago.
Category: Chevy
Expert:  rpmdiag replied 8 months ago.

Hi, I'm Ron and I will be helping you today.
Stand by for a moment while I prepare your answer.

Expert:  rpmdiag replied 8 months ago.

That's correct, it has to be a 5 volt reference. This means that if your grounds are good, then the PCM can be bad. You really should check the wave form of the MAF with a scope to be sure that the MAF is indeed good and NOT consuming the .9 of a volt. See attachment.

Thanks, Ron

Customer: replied 8 months ago.
I replaced the MAF with a used one i believe is good but the code came back up and i did check for 5 Volts at the wire coming out of the CPU and got 4.1 it drops down to 3-at the other end of the wire
Expert:  rpmdiag replied 8 months ago.

Then I would be checking into the PCM closer if you're satisfied that the grounds are okay.

Thanks again and please remember to rate me 5 stars and keep this link in case you need me again later on.


Expert:  rpmdiag replied 8 months ago.

Hi, I’m just following up with you to see if there are any more
questions you may have.