2000 Chevy Suburban Service Engine Soon Light P0171 & P

ADZCOM

MEMBER
2000 CHEVROLET SUBURBAN
V8
4WD
AUTOMATIC
130,000 MILES

Hi, I have read so many threads concerning this Service Engine Soon Light and am still stumped as to what the solution is. After scanning the vehicle I find these codes:

P0171 System Too Lean (Bank 1)
P0174 System Too Lean (Bank 2)

At last service, fuel filter, fuel pump, air filter, pcv valve and battery were changed. Transmission was also flushed. Belts were inspected as good. This was all done 3 months prior to light coming on. I dont know whether this is related but temperature dropped to -4F/-20C. Unfortunately I wasnt prepared and had a cold start which caused the engine to crank slowly before finally starting. Drove to gas station filled up and 2 minutes driving away, the light came on. Its been 2 weeks and I have tried tightening the gas cap, changing the location where I fuel and switched from using 87 to 91. I now also park in a heated garage. Light comes on stays on a few days, clears itself for another day a so and then comes back on. On cold days, light definitely stays on and I also hear a low whistling sound when accelerating. After lifting foot off accelerator sound goes away but when I step on the gas again, the whistling sound comes back. Also on cold days, when starting engine, noise comes from belt area. Noise disappears after driving for a while. I have been told by the parts stores to change 02 sensors. Whats the problem? My Service Engine Soon light needs to go! I appreciate any assistance!

1 Reply

BLUELIGHTNIN6

MECHANIC
16,542 POSTS

Hello
Thanks for the donation.

These codes usually indicate faulty oxygen sensor(s), however it can also indicate a vacuum leak. Since you state that you hear a whistling noise (usually indicating vacuum leak), I suggest checking for a vacuum leak at all vacuum hoses, especially the vacuum hoses near the throttle body. To find a vacuum leak, first thing to do is to listen carefully at each hose for a hissing/whistling sound. Next, use a can of carb. cleaner/WD-40 to spray any suspected hose(s). If you hear the engine change RPMs, you have found a leak.

You can also test your oxygen sensors just to ensure they are not faulty. Just follow the link below and read the instructions carefully for testing your 02 sensors.

https://www.2carpros.com/how_to/how_to_test_oxygen_sensor.htm

Hope this helps..
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