Hi

I bought a 2001 LS430 with 200.000 miles last October and on the way home the check engine light came on.
Code P0125. Insufficient Coolant Temperature For Closed Loop Fuel Control.

Since then I have changed the front O2 sensors on the left and right side (after that the light was off for 4 weeks, but then came back on again),
I checked the fuel cap and lubricated it,
I changed the temperature sensor,
I changed the thermostat,
I changed the battery,
I made sure there is enough coolant.

What else can I do?
When I delete the Code, or unhook the battery for a minute, the code is gone. Then I can drive for a day or two and then the Check Engine Light comes back on again.
It comes on after driving for a while - at least 15 minutes, by then the engine is defiantly in operation temperature.
It does not come on, when I start the car.

Please let me know what else I can do. I was really looking forward to this car, but I was not able to enjoy it at all. This check engine light drives me crazy.

Thank you!!

 

Is the temp gauge right below the half mark once the engine is fully warmed up?

 

Hi, thank you for the quick reply.
Here is a screenshot from a gauge in the internet,
i drew a read line where the needle is at, once the car is warm.

It is always above the white line, which is just below the middle.
I can take a picture of my car tomorrow, if that helps.

 

Read live data with a scanner to see what the computer is seeing from the ECT sensor. Could have gotten the wrong one or it's defective.

 

Can you recomend a scanner? I did buy one at amazon, it worked on all the other cars of my household, except on the Lexus. When plugged in, not even the light came on.
So I sent it back. If you have a name or a link, that would be helpful.
The ECT sensor I bought was an OE equivalent, and having a broken one and then buying a broken one by accident, does not seem very likely. I am sure it must be something else.

 

What brand of O2 sensors did you install? That code is set when the O2s don't ever send a rich mixture signal to the ecm. It's caused by defective O2s, vacuum leaks, low fuel pressure, defective fuel injectors, or an exhaust leak. The fact that it went away for a month after new O2s were installed points me to defective or contaminated sensors.

 

I installed the O2 sensors from Denso, which I think are the right ones. Is there a way to find out which of your suggested problems would be the right one?
I did get the code read out by a friend, but it was not at a Lexus dealer. Do you think they have a more sophisticated way of reading out the code at the dealership, that would give me more information of where the problem lies?
Or which sensor might be faulty?

 

the first step if no light it on the scanner and it works on other cars then check the fuses in the two fuseboxes under the dash.

Second step is does the scanner still work on other cars now? Is it's battery flat or pins bent etc.

If you need a new scanner, I recommend either a reasonable quality elm327 based dongle like an obdlink mx or similar and a phone app like 'car scanner' (free and it works on Android phones) or obtain a techstream cable for your pc.

 

Thank you for your reply. I just ordered another elm327 scanner. I had sent the other one back. I dont think it was because of fuses - I was able to scan the car with a scanner my friend had. But it was one where you could not read out anything but the code itself.

If the problem is with vacum leaks - how would I go about finding the leak? Or if it is a vacum leak at all?
If its low fuel pressure - would I be able to notice something while driving?

I have to mention, that the car drives just the same, (very good in my opinion, lots of power) no matter if the light is on or not.

 

When your new scanner turns up, try the app "Car Scanner'. It's the only app that I know of that will actually talk with the ls430.

I doubt a vacuum leak is causing it to run too cool or to throw that code. However removing air leaks is a good thing to do.

First step is to look at and feel the rubber vacuum hoses (especially the PCV line and the Fuel vapour line - also known as the VSV - it's the one with solenoid halfway back of the manifold on the left hand side of the car) .

If they are nice and supple and rubbery, then the chances are that have been replaced already.

If they are like old hard to touch and/or visually cracking rubber then you know it is time to replace them. You can easily get all the replacement rubber from an auto parts store in cut to size lengths for a few bucks. My advice is to drive to the closest store and just replace them one by one. It'll take less than half an hour to replace all of them if they need it.

 

And in reference to the coolant temp - you should checkthe wire for continuity between the sensor and the ECU.

 

Best/fastest/easiest way to find a vacuum leak is to spray brake clean at suspected leak points. After listening to the engine to try and get a rough idea of where air hiss is originating from, give it a small spray. If the engine stumbles when you spray a suspect area that's a leak point

 

We checked the wire from the sensor - it looked fine. Also my mechanic said, that if the wire was damaged, it would throw a code immediatly and not after driving for a while.
I will check the vacuum hoses with him next time I am there.

 

If the car runs fine and has power I would guess it's not a vacuum leak or fuel problem as there would be other codes. Whichever scanner you end up with make sure it reads live data. You can monitor the O2 outputs and make sure you get the full voltage swing on both sensors.

 

So just to clarify, is the code that keeps getting triggered the same "too cold for closed loop"?

There is only one temperature sensor.
And you have replaced it anyway.
Checked the wire for continuity (multimeter) back to the ecu... well that's the obvious things out of the way.

when the code is cleared it stays off for a day and then returns.

Are there any other symptoms or observations at the time that the code is set? Hesitations? Temperature guage reading? Time after start up? Is it random or always about 2-3 minutes after start?

Let us know when your new scanner turns up.