'02 Chevy PU Trouble codes 0174 & 0171


#1

I’m back for further advice. This PU sets the trouble codes 0171&4 when warm or the when it has been driven 3 miles on a cold morning. Codes do not set when driven in 70 degree ambiant temperatures. I was advised to clean the MAF sensor so I bought a can of cleaner and followed the directions. You are correct, it didn’t work. What’s next guys? 02 sensors?


#2

In troubleshooting a problem, symptoms aren’t enough. Tests need to be done. One can start with a suspect list; but, they are still only suspects until proven guilty.
The next suspect is the engine coolant temperature sensor (ects). The tests are: ohms, and voltage checks, with a multimeter, of the ects.


#3

Since it’s lean on both banks you also need to check for a vacuum leak that affects both banks or possibly low fuel pressure.

If you change the O2 sensors, your shiny new sensors will still tell you that it’s lean on both banks.


#4

I’ll check the fuel pressure, however, I figured that if fuel pressure was an issue, I’d get a fuel pressure or injector code. I’ve tried spraying carb cleaner around to find a vacume leak with no luck.
Why do you think about the temperature issue and why is this an intermittant problem and not an all the time situation. I figured it to be electrical since it was intermittant.


#5

So these newer electronic wonders/blunders even monitor fuel pressure. I did’nt know that.

Looks like a defective MAF sensor or vacuum leak are the most likely probs.

As for the temp thing, it seems something is heat sensitive & causing the problem. On some Fords the intake manifold O rings will leak cold but not when the engine is warmed up.

I was going to post the PO171/174 trouble shooting flow chart from my Hyundai shop manual, but vtcodger2 posted this very good link for this problem in another thread. (Thanks vtcodger2)

http://www.obd-codes.com/p0171