2000 Chevy Suburban Service Engine Soon Light Code P0171 an

Tiny
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 your assistance!
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Wednesday, January 7th, 2009 AT 12:32 PM

6 Replies

Tiny
JDL
  • EXPERT
My info says if both codes set together, to suspect fuel pressure or maf sensor.

I'm not saying to replace anything, you need to check fuel pressure and put a scanner on it, so you can see engine data, the freeze frame data should show what was going on, when the codes set.

I can't rule out an o2 sensor problem.
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Wednesday, January 7th, 2009 AT 3:33 PM
Tiny
ADZCOM
  • MEMBER
I have just cleaned the MAF sensor. Didnt really notice anything wrong with it. Is it supposed to look noticeably dirty if it is a problem? Hopefully, I did a good job. Now I just have to wait and see if the light stays off. Do you think that the whistling sound when accelerating and the noise from the belts are related or a different problem altogether? If fuel pressure is the problem, how do I fix that? Again, thanks for your assistance.
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Wednesday, January 7th, 2009 AT 4:54 PM
Tiny
JDL
  • EXPERT
I doubt you can tell anything by looking at the maf sensor. I'd put a scanner on it, that shows live engine data, you can see what the sensor is doing. A contaminated maf sensor might underestimate air flow at higher rpms.

As far as the whistling noise, do you think you might have a vacuum leak somewhere?

With a fuel injected vehicle, a fuel pressure gage is just like a screwdriver, you got to have one in the tool box. That way you don't have to wonder about fuel pressure, you can check it.
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Thursday, January 8th, 2009 AT 9:02 AM
Tiny
ADZCOM
  • MEMBER
OK its been 2 weeks since the service engine light has been off after I cleaned the MAF. I have driven over 400 miles. During that time, the temperature has also warmed up to 7 degrees Celsius. Today the temperature dropped to -17 Celsius and the light is back on. Is it likely fuel pressure, MAF or o2 sensors?
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Thursday, January 22nd, 2009 AT 8:59 PM
Tiny
JDL
  • EXPERT
Hi, i'd have to put a scanner on it, that way I can look at fuel trims and see what the sensors are doing.

As far as the fuel pressure, I'd put a gage on it.

You might gently tap on the maf sensor, to see if the engine acts up or the mil?

As far as the odds, of which sensor it might be? I don't know.
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Friday, January 23rd, 2009 AT 7:45 AM
Tiny
ADZCOM
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Thanks a bunch for your help. I'll try that!
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Friday, January 23rd, 2009 AT 12:09 PM

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