Check Engine Light P0125 P0171

I have a 2002 Tacoma 2.7 Automatic with 300k on it. I recently cleaned the throttle body out and it had a lot of carbon and oil build up. I put new gaskets on the throttle body and started it up. It had excess carb cleaner from me trying to clean out the intake as best i could without removing it. So it was a bit hard to start and once started blew nasty smoke until it cleared up and seemed to run better than it ever has.

Then a few days later i got a check engine light. I figured that it was oil and carbon that was in the intake that made it's way to the O2 sensors and thew a CEL. So i pulled the O2 sensors and they looked clean but i cleaned them by soaking them in carb cleaner and flushing the holes out. I reinstalled them and disconnected the battery cables and touched them together to clear the codes. But the threw a CEL again so i just took it to O'Reilly and let them run a scan on it. They came back with a P0125 Insufficient coolant temp for closed loop fuel control. And P0171 System too lean bank 1.

I assumed that it was going to be the O2 sensor but after some googling it seems that P0171 is usually a MAF sensor or a vacuum leak. I will check for a vacuum leak tomorrow since i did have everything apart to clean the throttle body. But when i looked at the PCV valve it was clean but seems broken. When looking down inside the hole from the top i can see a sideways spring and seems there is a metal ball under it. Nut sure if the spring is supposed to be sideways...

This truck is also a California emissions truck if that helps.

 

Could both of these codes point to the #1 O2 sensor? That's what I'm leaning towards since it threw it after cleaning the throttle body and rolling smoke out of the exhaust afterwards.

 

I think i just fixed the problem. The intake boot clamp right after the MAF sensor was loose causing a vacuum leak. I tightened it and disconnected the battery to clear the codes and it runs better now. Took it on a short drive and it had not thrown a CEL yet so i hope this fixed it.

 

Doesn't sound like it has had time to rerun the readiness tests. I dont think a vacuum leak would cause a p0125. Drive it a few more times and longer or attach your scanner and see if the monitors have been run. Sounds like you might still have a coolant sensor or thermostat problem.

 

I don't have a code scanner i let my local parts store scan it.

The truck ran really good at first then all the sudden it thew a CEL and started running odd. I took all of the intake tubes off to clean the throttle body and i forgot to tighten 2 of them but one was really loose. I think then it was first put on the boot was kind of in a bind from wedging the rubber tubes back on the aluminum MAF housing. Then after i drove it the vibrations cause it to fall into place and then started leaking.

I did a lot of researching the P0125 code and it seem that on Tacomas that code is more for the O2 sensor than coolant temp. So i was for sure i had to replace the O2 sensor i was about ready to whip out the credit card and buy both Denso O2 sensors from rockauto. But then i fell down the rabbit hole of Vacuum leaks and there is a good video of it on youtube on a 2.4 tacoma.

I am assuming the P0171 from the leaking MAF sensor then triggered the P0125. That's just a wild guess but it all started after cleaning the throttle body. And when i pulled the O2 sensor out it was clean there was no oily residue or carbon anywhere on it. But if it throws another CEL for the P0125 i am going to replace the O2 sensors. But for now it seems good i have been running it for a while now and it has yet to trip it again.

 

Still no CEL looking good..... Seems a loose intake boot clamp can cause a lot of havoc

 

Check engine light is back i wont have time to take it in for a new scan for a while. I am assuming the P0171 is probably fixed from tightening the intake boot clamp. So i think the P0125 code will still be there but i should probably order a new Denso just to rule the O2 sensor out. It has 300K miles on it and blowing a bunch of carb cleaner mixed with carbon and oil out of the exhaust might have done it in.

 

I just replaced the #1 O2 sensor and truck runs better. So far the CEL has not came back but i will try to give an update on it in a week or so. I hope this helps anyone else searching for a P0125 code.

 

I think you're on the right track. The P0125 (at least for 1996) is because the O2 sensor doesn't register a rich condition 140 seconds after starting the engine while these conditions are met continuously for 1.5 minutes: RPM > 1500, speed 25-62 MPH, and throttle open.

A vacuum leak could cause this or the heater circuit in the O2 sensor isn't working and doesn't heat the sensor soon enough. With the O2 sensor too cold it can never register rich. The exhaust gases usually heat the O2 sensor, but to get better emissions around this era they added a heater to get the O2 sensor temperature up sooner, so the engine could go into closed loop and get better emissions soon after starting the engine.

The P0171 is system too lean which could be several things, vacuum leak, low fuel pressure, blocked injector, bad MAF or O2 sensor.

The repair manual only points to the heater or heater circuit (wires) for P0125, but I could see how a vacuum leak could trigger it to.

P0135 or P0141 would indicate the heater circuit is drawing too much or too little current, and since you don't have one of these codes it may not be the O2 sensor. But these are 2 trip logic, so maybe they just haven't triggered yet.

Anyway, it sounds like you should check for vacuum leaks, then replace the upstream O2 sensor especially if it's old. And check for any problems with the wiring like a broken wire at a connector.

You can get a OBD2 scanner for cheap under $20 that hooks to a smart phone by bluetooth and graph out the output of the O2 sensors and check other sensor output.

 

I already fixed the codes further back in the thread. The P0171 was from forgetting to tighten 2 of the throttle body clamps. The P0125 was caused by a bad O2 sensor. The CEL is still off and normally it would have kicked back on by now so i think it's all fixed now.

 

This is my last check in on this thread. My check engine light has not come back on so I'm happy the O2 sensor fixed my P0125 code.