Mechanics

CHEVY P0171 P0174

2003 Chevrolet Suburban

Engine Performance problem
2003 Chevy Suburban V8 Four Wheel Drive Automatic 80009 miles

Im Having Lean Codes set on my Suburban, I have changed the MAF sensor as it intermittantly sets this code aswell. I have checked the wiring to the MAF and it has the battery voltage as asked for through Mitchell, I have checked for vacuum leaks at the intake, all vacuum hoses and the intake boot both with brake cleaner and with propane, I have cleaned the fuel Injectors with Champion cleaner introduced into the fuel rails, I have monitored the 02 sensors and they are fluctuating from mid 30mv to 800mv and reacting fast, The fuel trim levels at idle are long term 25% and short term 56.1% off idle they do adjust and at cruise long term go to 14.8%
the Alcohol content is 7% normally and in the freeze frame it shows 0%.
In the freeze frame data I get when the code sets I am concerned with one data aspect that says " commanded gear 6" and when I look at the T.O.S.S it is well above 4000 or 5000 rpm.
I also checked the battery terminals and they were dirty but I have since cleaned them and still am having the problem. I have the entire freeze fram peramiters when the codes set if you want them all I can Give them to you.
Thanks for the help
Avatar
Simon1974
December 16, 2008.




Acutally you did quite a bit of testing, I would check the intake again for vacuum leaks, very common on these vehicles. I would also unplug the mass air flow sensor and see if the fuel trims go to 0 also check for a plugged exhaust this will cause a lean code. Also check the air filter a plugged filter will cause this code. Check fuel pressure and check fuel filter. A plugged fuel filter will also cause a lean code. Check for an exhaust leak that will also cause a lean code. Check vacuum lines for cracks and pcv sys, make sure it's not plugged. Post the freeze frame data and I will look at it. These are some suggestions to check, lean and rich codes are very hard to diagnose because so many things can cause it. Please post back with what you find.

Brian 1
Dec 16, 2008.
The air and Fuel Filters are both new, I visually can not see a exhaust leak and I can not hear one, I checked the vacuum lines and they are all in good condition, the pcv system operates good. With a hose to my ear I do hear alot of sucking from near the elbow on the pvc hard line but I can not see a crak or leak under the foam when I inspected it. I unplugged the MAF and it goes to 0.0 on Fuel Trim.
The freeze frame data is as follows.
P0101
Engine speed 1483
ECT 14 DegF
Veh. Speed 0
App Ave 0
acc ped pos 15%
Barometric pressure 28.12 inHG
Commanded Gear 6
Desired idle 1050
Engine Load 5%
Run Time 7 seconds
Fuel Alcohol level 0
Fuel Comp Sens Freq 4Hz
Fuel Tank Pres. SenV 1.61V
Injector PWM Bk1 and Bk2 6.38
Long Term Trim Bk1 and Bk2 13.3
Maf 11.67 g/s
Map 10.34 inHg
Short Term trim Bk1 and Bk2 0.0
Start up Coolant Temp 14 DegF
Tp andle 14.1%
Tp angle Desired 10%
Traction Control Inactive
Trans OSS 4641 rpm

P0171B
Eng Speed 1188 Rpm
Ect 190 DegF
Vehicle Speed 0 Mph
App Ave 5%
accel ped pos angle 15%
Baro 27.90 inHg
Commanded Gear 6
Desired Idle Speed 550rpm
Engine Load 5%
Runtime 3 47
Fuel Alcohol 0
Fuel Comp Sens Freq 4 Hz
Fuel Pressure SenV 1.73V
Injector PWK Bk1 4.21 Bk2 4.1
Long Term Fuel Trim Bk1 and Bk2 25%
Maf 11.96 g/s
MaP 14.47 inHg
Short Term Bk1 -10.9 Bk2 -13.3
Start Up Temp 181 DegF
T.P. Angle 15.5%
T.P. Desired angle 10%
Traction Control INactive
Trans OSS 5121

P0174B
Engine Speed 1168 Rpm
ECT 151DegF
Vehicle Speed 32MPH
App Ave 8
Acc Ped Pos Ind Angle 15%
Baro 27.90 inHg
Commanded Gear 6
Desired Idle Speed 588 rpm
Engine Load 5%
Engine Run Time 2: 27
Alcohol Content 0
Fuel Comp Sens Freq 4Hz
Fuel Tank Press SenV2.02V
Injector PWM Bk1 4.14 Bk2 4.23
Long Term Fuel Trim Bk1 and Bk2 25%
MAF 13.67 g/s
MAP 12.70 inHg
Short Term Fuel Trim Bk1 3.1 Bk2 3.9
Start up coolant 117 DegF
Tp angle 16.8%
Tp Desired Angle 10%
Traction control Active
Transmission OSS 5121 RPM

Tiny
Simon1974
Dec 16, 2008.
Looking I did not know that it had a p0101 code, this changes things, what I want you to do is take the pcv hose off and remove the insulation and check for cracks.I've had 07 silverado's with the same engine has a cracked pcv hose. Also if you can take an exhaust back pressure reading. When you punplugged the mass sensor and it went to 0 that means you are by-passing the mass air which usually means that it's bad, but before you do anthing else I found a bulletin on the p0101. Read it. This message applies to all 1999 through 2004 Chevrolet, GMC, Olds, Buick and Cadillac pick-ups and utilities that are equipped with either the 4.8 liter, 5.3 liter or 6.0 liter Gen 3 V-8 engines. Recent warranty analysis indicates that both the MAF, or mass airflow sensor, and the MAP, or manifold absolute pressure sensor, are being replaced for a MAF sensor code P0101. The cause may actually be a MAP sensor failure causing the MAF sensor code. One of the MAP sensor’s primary functions is the calculation of the speed density formula, which is compared to the MAF sensor reading. Should the MAP sensor fail, the PCM may interpret this as a MAF sensor concern and set a P0101 code. If diagnostics are followed thoroughly the technician may find a MAP sensor failure causing this condition. In conclusion, when a MAF sensor code of P0101 is found the technician needs to verify the proper operation of the MAP sensor before concluding that the MAF sensor requires replacement. The fuel long term fuel trims should be -10 to +10 but as close to 0 as possible. You said you replaced the mass air before, see if you can get another one you might still have a bad one. Post back with what you find.

Brian 1
Dec 16, 2008.
I did all of the above, I rechecked the PVC hose and it help vacuum for the last 2 days at 19 inHg but I did put a new hose on and it seems to of fixed it, I dont know if maybe it is the rubber hose on the ends.
For now it seems to be running good, thanks for the help

Tiny
Simon1974
Dec 19, 2008.
Thats great glad I could help.

Brian 1
Dec 19, 2008.
Not so Lucky. It has come on again the Fuel Trim looked fine. Im thinking of doing the intake as I have no Idea what else it could be.
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Tiny
Simon1974
Dec 23, 2008.
You said the fuel trims looked fine, what were they at?Only other thing I could suggest is take an exhaust back pressure test if you can. Check the o2 sensor connections for water intrusion. Last thing clean the fuel injectors AT THE RAIL. One other thing, you might have to have the injectors themselves tested also. I had the same problem with my wifes G6 and I did all the same testing you did and went round and round, finally I figured out what it was, I had to replace all 6 injectors and it fixed it. But I'm not saying this is the problem but I would not rule it out. Post back with any other questions. Thanks for keeping me updated.

Brian 1
Dec 23, 2008.

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