Mechanics

CHEVY CODES P0170 & P0171

2003 Chevrolet Suburban

Computer problem
2003 Chevy Suburban V8 Four Wheel Drive 56,000 miles

Check engine light came on in 2003 Suburban, had Auto Zone run a Check and returned Codes P0170 and P0171. They recommended O2 Sensors. Looking around there seems to be some disagreement on this as a solution for these codes together. Majority point to dirty MAF Sensor and suggest cleaning that. Any recommendations here on the best course of resolving this?

Thanks,
Hank
Avatar
HankO3rd
November 19, 2008.




I don't believe the 02 sensor is your problem.

A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty.

Note: The use of " oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.

There could be a vacuum leak downstream of the MAF sensor.

I suggest doing the following before replacing anything.
In the vast majority of cases, simply cleaning the MAF sensor does the trick. If you need instructions on doing this, just let me know and I will post them here for you.
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure.

Bluelightnin6
Nov 19, 2008.
Thank you. Yes, please post the instructions for cleaning the MAF sensor. Also, how do I check for a dirty fuel filter? For fuel pressure I assume I'd get a fuel pressure guage. Thanks again for your guidance.

Hank

Tiny
HankO3rd
Nov 19, 2008.
First, remove the MAF sensor from the vehicle. The MAF sensor should always be located in the air duct between the air filter and the throttle body.

Picture of MAF sensor connector location (1) and flow direction (2) for 2000-2005 4.8L, 5.3L, 6.0L engines below.


http://www.2carpros.com/forum/automotive_pictures/261618_0900c152800a6a9e_1.jpg



NOTE: DO NOT USE CARBURATOR CLEANER!

To clean, spray some electrical contact cleaner (something that leaves NO residue) through the sampling tube over the wires. I recommend using a MASS AIR FLOW cleaner from your local auto parts store. It is specially made for this job and only costs a few dollars.

Start with this first, post your results and if it doesn't help your issue then we will go on to the fuel filter.

I think this will do it for you though.

Thanks for using 2carpros.com!

Bluelightnin6
Nov 19, 2008.
Thanks. I'll do this tonight and see if it makes a difference. I'll let you know the results. Offhand do you know when the check engine light will reset if this is the solution?

-Hank

Tiny
HankO3rd
Nov 19, 2008.
In most cases, you will have to disconnect the battery for 10 minutes and reconnect it to reset the engine light. You can also have AutoZone delete the code the same way they ran the diagnostic scan for you. It should stay out, if it comes on again then you need to have it scanned at AutoZone again to see if it is same codes.

Bluelightnin6
Nov 20, 2008.
I cleaned the MAF Sensor and replaced the air filer at the same time. There was a slight improvement, however, when idling it " lopes" between 4,000 and 6,000 rpm-not dying but sounding close. Oddly when it drops to the 4,000 rpm mark the lights dim. The check engine light is still on, I was negligent (read as lazy) and haven't cleared the codes, so I cant offer anything there.

Thanks,
Hank

Tiny
HankO3rd
Nov 21, 2008.
Was it idleing incorrectly when you first posted? Because you neglected to state that, if so.

I suggest having the codes erased and read again in order for me to better assist you.

Bluelightnin6
Nov 21, 2008.
Ok, This is the exact same problem that I have been having for 3 years! It runs GREAT in the summer when it is warm out, but when temps drop to cold ( around 40 deg) I get a really rough idle and sometimes will die. I got the exact same codes from Auto Zone so I bought a MAF and NOTHING changed. I have taken it to 3 places and noone can figure this out. When the temps go back up the rough idle stops and it runs like a champ. This has us so stumped it is not even funny. Super annoying when it dies dropping the kids off in the school line. ANY help in this matter would be great. Thanks.
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Tiny
Oysifly
Dec 3, 2008.
Okay, I have the same issue.I replaced teh MAF Sensor and seemed to make a slight difference in performance. But I am still having the same problem. Here are my symptoms: 1. Prior to replacing the MAF Sensor, the idle did flex between 4k and 6k. It did die once and the outside temp was very cold (25 degrees).

2. After one day of smooth performace the check engine light came back but the idle seems okay.

3. I added some injector cleaner as well, the PO171 code indicated possible fuel injector problem as well.

Autozone also said that the problem could be a result of a faulty cooling system sensor?

Any help would be really appreciated.

Ryan

Tiny
Rburton21
Dec 23, 2008.
If your engine is idling up and down like that then I would suspect a faulty IAC valve (Idle Air Control Valve). Located on throttle body.

Bluelightnin6
Dec 24, 2008.

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