Codes P0171 and P0174 this weekend
Thread Starter
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Codes P0171 and P0174 this weekend
Last weekend, during a trip to Canada, I got a CEL light on my Vortech supercharged 02 coupe. No driveability issues until a Sunday autocross.
The trip to the autocross site started with the CEL on but it went out after about 10 minutes. Still no driveability problems.
After the 3rd a-x run, the CEL came back on and while the car ran fine under power, the idle speed was very low (engine died a couple of times) and was fairly rough. This went on throughout the day.
On my trip home, the CEL light never came on, everything seemed to run fine at cruise speed but I still had a very low and rough idle. I could feather the throttle and eventually the idle would smooth out and I saw the usual 800 RPM.
The only codes displayed are the P1071 (Fuel Trim system Lean Bank 1) and P0174 (Fuel Trim System Lean Bank 2). Both show as history codes and prior to the weekend, there were no PCM codes shown so the two codes had to come from whatever this problem is.
Ideas??
The trip to the autocross site started with the CEL on but it went out after about 10 minutes. Still no driveability problems.
After the 3rd a-x run, the CEL came back on and while the car ran fine under power, the idle speed was very low (engine died a couple of times) and was fairly rough. This went on throughout the day.
On my trip home, the CEL light never came on, everything seemed to run fine at cruise speed but I still had a very low and rough idle. I could feather the throttle and eventually the idle would smooth out and I saw the usual 800 RPM.
The only codes displayed are the P1071 (Fuel Trim system Lean Bank 1) and P0174 (Fuel Trim System Lean Bank 2). Both show as history codes and prior to the weekend, there were no PCM codes shown so the two codes had to come from whatever this problem is.
Ideas??
on this one. Same thing happened to my '04 Suburban this past weekend.
Former Vendor
Joined: Mar 2006
Posts: 153
Likes: 0
P0171 indicates a lean condition on the driver's side while P0174 indicates a lean condition on the passenger side. If you are getting both codes, the problem is most likely a global problem like bad gas or a potential leak somewhere in the intake system after the MAF. If you are only seeing one of the codes, then it can be related to something specific to that side of the engine like an exhaust leak or a bad injector.
You can read a complete description here.
You can read a complete description here.
Pro
Joined: Oct 2006
Posts: 734
Likes: 0
From: Bryan Texas
I was getting P0174 codes after the car ran badly a few times. I could smell raw gas even. I assumed it was detecting a non-existant lean condition and started dumping gas into it. I replace the o2 sensors and have not had anoymore problems. I was also getting o2 sensor codes as well.
Thread Starter
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Found the problem! 
I have a Breathless Performance Vortex air intake system on the car and somehow one of the band clamps holding the coupler from the back side of the MAF to the bridge came loose. Apparently it was allowing enough extra air to flow into the engine from behind the MAF to cause enough of a lean condition to cause the codes to be set.
The low and rough idle was due to the same thing; the bridge would move around slightly as the engine idled and the gap would increase and decrease.
Once I tightened up the clamp and made sure that everything was tight, the rough idle went away.
Sometimes it pays to check the basics :o
John: thanks for the link, good read.
I have a Breathless Performance Vortex air intake system on the car and somehow one of the band clamps holding the coupler from the back side of the MAF to the bridge came loose. Apparently it was allowing enough extra air to flow into the engine from behind the MAF to cause enough of a lean condition to cause the codes to be set.
The low and rough idle was due to the same thing; the bridge would move around slightly as the engine idled and the gap would increase and decrease.
Once I tightened up the clamp and made sure that everything was tight, the rough idle went away.
Sometimes it pays to check the basics :o
John: thanks for the link, good read.
