P0171 and P0174 Lean condition on my new LX470 ... (2 Viewers)

[cwmoser]

Got a Check Engine light this morning.

My ELM327 scanner says the fault is:
P0171 – Powertrain System too Lean (Bank 1)
P0174 – Powertrain System too Lean (Bank 2)

This is a new to me 2002 LX470 with only 25K miles.

What's the thinking about how to troubleshoot this issue?

 

[CurbsEnthusiasm]

30 seconds ago I mentioned this truck to a friend and now your having issues!

My first thought was o2 sensor...

 

[cwmoser]

One maintenance record shows that O2 sensor Bank 1, Sensor 1 was replaced because of a Check Engine light 500 miles ago.
(This was done by an independent Lexus service center, not a dealer service center)

I read that both P0171 and P0174 could mean an air leak, MAF sensor, clogged Fuel Filter, or bad Fuel Pump.

Where is the pressure port to measure Fuel Pump Pressure and what is the acceptable reading?

I've just received the Mini-VCI interface cable to a PC but have not used it. Will it point out the problem area?

Don't want to but I might have to take it to a Lexus Service Center.

 

[2001LC]

How's gas cap do you hear air suck in when loosened? Disconnect battery for 30 minutes while cleaning MAF to reset ECM. As always clean & re-grease battery post when every disconnected.

Is it running ok? Lots of bad gas around clogging fuel systems.
Quick low fuel pressure test, is to pinch off return fuel line. (Edited: Pinching could damage line!) If idle comes up, or runs better would indicate need for fuel pressure test.

 

[cwmoser]

How's gas cap do you hear air suck in when loosened? Disconnect battery for 30 minutes while cleaning MAF to reset ECM. As always clean & re-grease battery post when every disconnected.

Is it running ok? Lots of bad gas around clogging fuel systems.
Quick low fuel pressure test, is to pinch off return fuel line. If idle comes up, or runs better would indicate need for fuel pressure test.

I do get a swoosh when I remove the Gas Cap.
MAF - I'll check to see if it is dirty and blow off any dirt /dust on it.

Fuel Pressure return line - I assume its under that fancy plastic engine cover?

Regarding Gasoline, I put in Premium when I took delivery. It did have 1/2 tank of "California gas".
Wonder also if the Engine can be retuned for non-California emissions settings?

 

[Julian Stead]

Normally its just the maf sensor, be careful as they are fragile, I would use a cleaner. Check for any green on the connections aswell. If this vehicle is new to you then do some checks to air filter, fuel filter, pcv valve, add a fuel cleaner and give it a blast up the road to clear out.

PCV valve could cause this also but it isnt so common.

 

[2001LC]

I do get a swoosh when I remove the Gas Cap.
MAF - I'll check to see if it is dirty and blow off any dirt /dust on it.

Fuel Pressure return line - I assume its under that fancy plastic engine cover?

Regarding Gasoline, I put in Premium when I took delivery. It did have 1/2 tank of "California gas".
Wonder also if the Engine can be retuned for non-California emissions settings?

Return fuel line comes from PS around back intake manifold then to area above fuel filter. The fuel inbound line is just to the left of this in picture, going under that round device (regulator) coming from fuel filter into fuel rail.

If you find pinching return line (Edited: Pinching could damage line!) helps. You could have on vehicle fuel injector cleaning done, followed up with can of 44K in the gas tank. Just make sure the shop that does the work also includes a pressure test as parts of the service. This will save you some $$.

Julian made good points, don't touch MAF wires, use a MAF cleaner only. I assumed you checked inbound air and all is good including Throttle body cleaning, before your OP.

Is engine running hot, cold or normal?

 

[cwmoser]

Thanks for the call outs of the inbound and outbound fuel lines and regulator.
I do find this information interesting. I am pretty familiar with component
locations in my Isuzu Troopers but this LX470 is a whole different animal.

BTW, where is the Fuel Filter located? I was reading some other postings that stated the
Fuel Filter is good for 100K miles. My LX470 only has 25K miles.

The Engine is not running hot. The Engine does seem to feel like it does not have as much
power as those that I have test driven. Was reading that a dirty MAF could cause these
symptoms too. Otherwise all is well with my "new to me" LX470.

 

[Julian Stead]

The fuel filter might last 100k but quality of fuel will have an effect, it might only have 25k but it's still 14 years old so don't just go by mileage, components can break down with age, especially a filter element soaked in fuel all its life. My filter is located at behind the battery on the inner wheel tube, mine is a UK spec landcruiser though.

 

[Julian Stead]

Low mileage cars can suffer with lack of maintanence due to PO's ignoring service interval dates, not saying yours has but It happens a lot. My trucks PO did that, 7k miles in 8 years, some years it was only driven to get MOT(safety inspection). So he ignored servicing to much, full Toyota service history up to that date but I've had to change all uj's due to lack of grease, no play but stiff, same for front wheel bearings and needle bearings. Ball joints where dry, brakes where binding. My timing belt will be done soon as it now only has 10k but it's still 8 years since the last.

Point being is to still do a complete checkover, then happy motoring.

 

[2001LC]

Typical the fuel filter is not a PM item, it supposedly designed to last forever. That said, I change mine out around 60K miles. Your LX with only 25K miles is unusually low. It indicates it was driven very short trip and parked for very long times, this brings it's own issue. Corrosion of fuel component's, gas tank lining being number one. The fuel pump to fuel injector may be clogged up. Try a can of 44k in tank first, then the on vehicle fuel injector cleaning to get that "free" fuel pressure test, if pinching return line gives any boost to RPM as suggested above..

Running lean means your not getting the desired amount of fuel. This will cause and engine to run hot. The temp gauge doesn't move very much in these (Mr. T didn't want us to worry). Some of the guy have a scan gauge (of some sort) hook-up while driving, to monitor the engine temp.

Do some reading up on issues common to vehicles stored for long periods. This will give you a road map to follow through systems that may have been effected.

Also consider getting the factory manual (FSM) it will be invaluable if you plan on DIY your own rig.

As note in picture above; follow the fuel line which in front of return line, out to the fender-well and you'll see the black cylindrical fuel filter.

I pull the 20A EFI fuse while engine running to cut fuel (cut pressure) before removing lines connected to fuel filter.

 

[cwmoser]

I'm not familiar with the fitting with the green color on it. Any hints?


I cleaned the MAF sensor with some cleaner. Then took my LX470 out for a spin.
I note that at cruising speed the Long Term Trim for both banks is over 20. Is this normal?

 

[Julian Stead]

The connectors can turn green from moisture ingress, which is a bad thing, as long as you they are clean your good to go.

 

[Julian Stead]

Sorry, is the long term trim a percentage, 20% is still lean, it should be close to zero.

 

[PADDO]

As a singular data point my LT trims always fell within +/- 3% (from 0) when I monitored such things. I know others have reported similar results. As I understand it figures less than +/- 5 % are satisfactory.

 

[cwmoser]

Sorry, is the long term trim a percentage, 20% is still lean, it should be close to zero.

My ELM327 reports LTFT1=21.9 and LTFT2=21.9 cruising at 1500rpm

I'm wondering if my ELM327 is reporting bad numbers though.

It reported 21.9 and 21.9 when I cranked my LX470 after it was sitting for a couple hours.
Then when I got back home and parked at idle it was 7.8 and 6.2

Engine Temperature is normal.

 

[PADDO]

After cleaning the MAF did you disconnect the battery (some say 10 mins, some 30) to clear the engine management memory? If not it can, apparently, take 10-15 mins of driving for the LT trims to stabilize and reflect what's really happening.

 

[Julian Stead]

If you are using Code reader you can use it to help diagnose the issue, don't think of the issue of running lean as such, as O2 sensors read oxygen, so it means there is to much oxygen. This can be a misfire as the oxygen isn't burnt, fuel delivery issue, vacuum leak, cracked exhaust or a faulty sensor somewhere. The sensors used to work out fuel strategy are O2 sensors, maf sensor, tps sensor and coolant temp.

You use the readings to help diagnose by reving engine to 2000 rpm hold it there for say a minute, if there STFT/LTFT starts to go within normal range then look for a vacuum leak, if the numbers start to rise then fuel starvation(blocked injectors or fuel pressure). Keep listening for a misfire, it only has to be slight. You can check oxy sensors by disconnecting a vacuum pipe and watching the STFT shoot up.

My money is on fuel pressure or vacuum leak as both banks read the same.

 

[Julian Stead]

Sorry a faulty sensor would make both banks read the same also.

 

[cwmoser]

I reved engine to 2000rpms for over a minute. LTFT1/LTFT2 started off at 21.9/21.9 and settled down to 14.8/15.6.
Then at idle (697rpms), LTFT1/LTFT2 = -3.9/-3.1 and STFT1/STFT2 = -0.8/-4.7.
At idle for some time seemed to stay at these numbers.

I did not notice any misfire.