AElexus

hello to all

Im new in this forum and hope to find solution to my problem.

I have 2002 lexus LS 430 and have encountered an
issue with code p0171 for almost 9 months. Tried all sort of solutions and googled it also tried to ask different people but no luck

PS: I changed all plugs
Changed all vacuum hoses with PCV valve
Changed manifold and throtellbody gaskets
Changed MAF sensor
Changed 1st o2 sensor in bank1
Changed air filter
Changed fuel filter and cleaned injectors by machine

Any advice would be much appreciated!

Thanks in advance

Doublebase

What code is that? A lean misfire code?

If so I'd look at a few other things besides what you already did. First I'd look at the parts you used, did you use an OE part for the O2 sensor? If not I'd start right there. I find that so many cars just don't respond well to aftermarket O2 sensors. So that would be the first thing I'd change if you have an aftermarket sensor in there - and I don't care if the guy at the parts store told you it was a high quality Bosch or Denso - go right to the dealer and buy an OEM sensor.

If that isn't it I'd check for a small exhaust leak ahead of the O2 sensor. Any flex pipe that has a crack in it would cause that code. I'd also check the exhaust manifold gasket on whatever bank the code is telling you is lean...then I'd just follow the exhaust all the way down to that sensor and check everything. Small leaks is what you're looking for, nothing obvious, just small enough to let a little air in and throw off the readings on that O2 sensor.

I'd also check the air filter housing and duct work to the throttle body, any broken clamp or tear in that duct work would throw that light. Something simple yet overlooked in a lot of cases.

You mentioned fuel filter and a injector cleaning, but how's your fuel pressure? Although if the pump wasn't doing its job the code wouldn't set to only one bank, it'd be both sides and you'd probably have a multiple misfire code.

Just some ideas, but I really would look at that O2 sensor. I'd even look at that mass air flow sensor if it isn't OEM.

AElexus

Thanks for your reply
P0171 means System Too Lean Bank 1
I don't have any misfire codes.
I'm always buying parts from dealer
​​​O2 and MAF sensors are OEM and bought from dealer.
Fuel pump pressure is ok
I checked all exhaust pipe no crack at all, even i changed catalytic converter gaskets.
I checked the air filter housing is fine and duct work to throttle body is also ok and so far found no broken clamp or tear

AElexus

P0171 ( system too lean bank1 ) and
P0125 ( Insufficient Coolant Temperature For Closed Loop Fuel Control )
I have both codes
Are the two codes related somehow?

rkw77080

According to the attached DTC chart, P0125 and P0171 have one common cause - the engine coolant temperature sensor. This is an easy DIY... Take a look at the post below for tricks and tips.
https://www.clublexus.com/forums/ls-...re-sensor.html

On another topic, do you have, or have you considered investing in a Techstream? If you're not familiar with Techstream, do a search here on this forum for more detail. It will be the best USD$30 investment you can make to diagnose your LS430 DTC issues.

AElexus

Thanks for DTC chart
I have replaced engine coolant temperature sensor with tharmostat but code ( p0125 ) pop up again.
I have techstream installed in my laptop

Tom57

Have you purged the coolant system of any trapped air?

AElexus

How can I do that?

Tom57

See post # 8 > https://www.clublexus.com/forums/ls-...flush-diy.html

rkw77080

Another possible culprit for temperature sensor issue can be the type of thermostat installed, and how it's installed (see drawings below for detail).

rkw77080

It very important that you install the thermostat with its jiggle valve at the 12 o'clock position to allow trapped air to pass. The temperature sensor will not work properly if it is not fully submerged in the flowing coolant.

Tom57

AElexus, we assume that you have checked coolant fluid levels at both the radiator (when cold), as well as the overflow reservoir (located underneath the plastic air intake which covers the radiator).

AElexus

Thanks Tom57 for link
Fluid levels at radiator and overflow reservoir ok

Tom57

After verifying that the thermostat is installed correctly with the weep hole valve at the 12-o'clock position (see rkw's posts above), carefully check all wires at the terminal / wire harness connection to the engine coolant temp sensor. Since you replaced the coolant sensor, the plastic connection gets brittle, and wires have been known to become disconnected.

AElexus

thanks alot rkw77080 for the explanation
Thermostat is OEM and bought it from the dealer.
​​I checked jiggle valve and unfortunately it was down 6 o'clock position .
Turned it right (to 12 o'clock position) and cleared all DTC codes​​​​.
Let's see what is happening now