P0174 (lean bank 2) but NO P0171

[MH_Stevens]

2003 Land Cruiser with 260,000 miles. Runs great (on new coils and plugs) but I have the difficult to diagnose Lean on Bank 2. I do NOT have the lean on bank 1 code. Does this help in diagnosis? Seems the error must be specific to that one side. Searched till the cows came home for vacuum leaks. Like others have reported the CE light goes of on a good run then reappears.

System reports fuel consumption an only 5.4mpg but I have not tested this with manual fuel measurement. New fuel pump made no effect.

Just need to know what i'm not finding any causes.

 

[OEMGUY0720]

Next basic steps would be to inspect your MAF sensor, then upstream and downstream O2 sensors actual condition. Check also your short and long term fuel trims if you have realtime data from your OBD tool.

 

[2001LC]

^^^^^.
Also consider, there are many sellers of bootleg coils and plugs. Where purchased, matters.

 

[andrewderrick]

Start looking for a vacuum leak that would only affect one bank.

 

[Aracobuilt]

I am currently going through a lean on bank 1 code, causing a slight rough idle and check engine light. I noticed the PCV valve grommet and hose was more of a hard plastic than rubber. I replaced them and noticed a considerable improvement but not a complete fix. I ordered and just received a few other vacuum lines, but I am not convinced my issue will be resolved. I am starting to feel that what seemed like a simple and straightforward fix is going to cause a lot of frustration. Might even need to resort to a smoke machine.

 

[OEMGUY0720]

I am currently going through a lean on bank 1 code, causing a slight rough idle and check engine light. I noticed the PCV valve grommet and hose was more of a hard plastic than rubber. I replaced them and noticed a considerable improvement but not a complete fix. I ordered and just received a few other vacuum lines, but I am not convinced my issue will be resolved. I am starting to feel that what seemed like a simple and straightforward fix is going to cause a lot of frustration. Might even need to resort to a smoke machine.

That’s actually the best route and eliminate the frustrating guessing game of an evap and/or vacuum or exhaust leak, I had good luck with this product.

 

[Gartenmeister]

I am currently going through a lean on bank 1 code, causing a slight rough idle and check engine light...... I am starting to feel that what seemed like a simple and straightforward fix is going to cause a lot of frustration.

My LX had lean bank 1 when I bought it. It ran fine. If cleared the P0171 code would come right back. I asked the local Toyota dealer to fix it, they started with cleaning MAF but that didn't work. Next they decided it needed a fuel filter, I was skeptical since the code was for just one side, but whatever, filters are cheap. It worked. 2000+ miles and no code. FWIW

 

[2001LC]

Sometime we only see a single BK lean DTC. When both, are running lean. The one BK, just happens to cross the DTC threshold, the other stay just below.
Watching fuel trims as we drive. Is a very useful tool.

Order I look

1. Tech stream data while driving i.e FT, ECT, AT temp,
2. Air filter & MAF. Just and east look. Usually results in a, Rich condition.
3. Vacuum leaks
4. Fuel pressure & flow.
5. O2's
6. Spark.
7. Compression.

Always look over:
Engine for signs of wire damage.
Cabin for water entry into dash and junction boxes.
Aftermarket wiring.

 

[lowenbrau]

My LX had lean bank 1 when I bought it. It ran fine. If cleared the P0171 code would come right back. I asked the local Toyota dealer to fix it, they started with cleaning MAF but that didn't work. Next they decided it needed a fuel filter, I was skeptical since the code was for just one side, but whatever, filters are cheap. It worked. 2000+ miles and no code. FWIW

I guess once they start to rust, it might be time to change them, This was a fresh paper towel. <barf>

 

[lowenbrau]

One more data point. 1999 LX470, 450,000km I had high LTFT in both banks. got a p0171 code that wouldn't stay cleared. Bought and used a smoke machine to look for vacuum leaks, found none. (thanks for the recommendation @OEMGUY0720) that machine is slick. It didn't help find any leaks but it gave much confidence that I didn't have any. Cleaned the MAF, no change 5.1 at idle. swapped the ugly fuel filter, finally reluctantly swapped the fuel pump and that did the trick. Surprising since the rig pulled hard to 160kph on the old pump. I guess quantity doesn't equal quality. Both short and long term trims spend most of the time near 0 now.