This past weekend my MIL came on. I plugged in my OBDII and got a P0171 malfunction code. System Lean Bank 1.

Truck:
97 F150 SC 4x4 OR
Gibson catback dual exhaust
K&N filter
88,000 miles

My first thought was the MAF is dirty but wouldnt both banks registered this error code?
What side is Bank 1, Driver?
Could this be an O2s? Isnt that a seperate error code?
Possibly a leaking intake manifold gasket?

Ive checked for vacuum leaks and havent found anything.
The code hasnt returned since I cleared it.

Thanks for any ideas.

Ron Hanson
http://www.flippebit.net

 

p0171 Lean means insufficient fuel. Fuel codes are 0170-0175. If it were an O2 censor, you would get a code between the range of 0130-0161. Too lean can normally be corrected by restoring adequate fuel pressure. Since your truck is running, you can rule out a fuel pump failure and changing the fuel filter will more than likely solve the problem.

 

If that code is fuel pressure related, could it be the code thrown when the gas cap isn't tightened well. Before I spent lots of money replacing stuff, I'd try retightening the gas cap, reset the computer and see if it throws it again. Well, I guess you might as well change the fuel filter with that many miles...

 

Taking into consideration that all cars made after the mid 90's had to be compatible and with similar DTC's. (diagnostic trouble codes). The lack of a properly tightened gas cap wil be a P0440 code. Emission system codes are between P0440 & P0446. good luck.

 

to: Ron Hansen, Clearing the code by disconnecting the battery will most likely only be a short term answer if you do have a bug.
Two Trip Logic will show you a check engine lite if the problem reoccurs. What this means is driving the truck 2 or more times with a minimal drivng time of 20 minutes should be what it takes to reset the check-engine lite. Keep us infomed.

 

Thanks everybody. I cleared the code with my Actron 9615. I also disconnected the battery so it could relearn it fuel trims. Unfortunately the light came on when my wife was driving so I dont know what she was doing so I could recreate.

Im still curious what side is bank 1.

This could be so many things Id like to narrow it down. I guess I'll look over everything this weekend and check for air leaks in the intake system and wait for it to come on again.

Throttle:
If it was a fuel pressure problem wouldnt it had leaned both banks and set an P0191 for fuel rail pressure?

My understanding of P0171 was the computer needed to compensate with an overly rich fuel trim to compensate for a overly lean condition on one 'bank'.

 

FYI: I found a good troubleshooting list for OBD codes here:

http://personal.riverusers.com/~mira.../2000_dtc.html

 

I recreated the error code. Passing at 69mph. According to the data freeze fuel trims look normal for the load:
Calc load: 58.4%
LT FL TRM 1: 22.7%
LT FL TRM 2: 21.1%
ST FL TRM 1: -4.7%
ST FL TRM 2:-1.6%

I checked the realtime data right after this happened and noticed
the O2 sensor #1 BNK 1 was reading 0volts intermittently. I dont think that is normal. Shortly after it started reading correctly.
I think my o2 sensor is going but not enough to trip the trouble code.

Now I just need to know what side is bank 1.

 

Ron bank one is the pass. side and yes if your 02 was reading 0 its bad but be sure to check wiring and connectors to the 02 before replacing it. good luck
DAVE

 

Thanks Dave
Ill post if I find the problem

 

Actually your comment about the fuel pump is not entirely accurate. the fuel pump for the f150 could be going out. and it could throw the code if the ecm recognises the fault during 3 consecutive cycles but I think that would not likely be the case with the OP's vehicle. It is possible one of the injectors on bank 1 is clogged. IF it were the fuel pump and the rest of the system is good then he would have both the p171 and the p0174.

 

yes if the rest of the fuel system is operating correctly and the fuel pump were the culprit you'd get poth the p0171 and p0174 because the fuel does go to both sides of the engine. My thoughts on this are either a clogged injector that is so miniscule that it doesn't cause the engine to have a noticeable misfire under general operating conditions, a leaking intake manifold gasket on bank 1 side or a vacuum. isse. It could also be the up stream O2 sensor and the codes for that could be either p0171 or p0420..

 

I would check the connector for a bad ground wire

 

You know you replied to a 20 year old post?