Fixed P0125 now have P0135.

[RUNMYTA]

HELP!! I had a CEL on my 99 Limited and had a buddy scan it and it had a P0125 low engine coolant temp. I replaced the Air/Fuel sensor (Cali model) with a DENSO and reset the computer by disconnecting the battery. Drove it about 10miles and CEL came back on. Took back to buddies to scan and now it has P0135 O2 Sensor heater circuit, but the P0125 is gone.

What could it be???:wtf:

 

[TheDurk]

HELP!! I had a CEL on my 99 Limited and had a buddy scan it and it had a P0125 low engine coolant temp. I replaced the Air/Fuel sensor (Cali model) with a DENSO and reset the computer by disconnecting the battery. Drove it about 10miles and CEL came back on. Took back to buddies to scan and now it has P0135 O2 Sensor heater circuit, but the P0125 is gone.

What could it be???:wtf:

Do a resistance check on the new sensor and clean the connections on both sides and see where that gets you. P0135 is very specific, and basically there is a wire loop from the ECU to the sensor heater and back again. Something along there is not right. You did get the correct Denso sensor number, right?

If the sensor passes, and the cleaning doesn't help, I think the FSM has a procedure for checking continuity from that end.

 

[RUNMYTA]

I have a Cali Emmsions so I bought the DENSO 234-9002. Verifed that was the right one on URD's website.
Clean the connections today with electric cleaner and also cleaned MAF. Cleared code via battery disconnect and still CEL light comes back on. Going to check resistance on O2 this weekend. Other than that I am still stump how this wasn't an issue with old O2 and now it is???

 

[DaveS]

If the sensor is good, as stated above there is likely a break in the circuit between the sensor and the ECU - either the plug that the sensor connects to is bad or there is a break in the wire leading from it to the ECU - you will need details from the fsm referenced above to find out the route it takes and where this wire goes into the ECU so you can start checking continuity

 

[Baja Runner]

Double check the ground that runs from the "Diagnostics" connector in the engine bay to the plenum.

The P0125 code usually means that the O2 sensor is bad, but, If it were me I would have checked the resistance of the ECT. It is weird that the code would change with the sensor. (Making me think that it is definitely the issue here)

You can also check the voltages at the ECM of the inputs of the sensors, but its essentially the same thing as hooking up a diagnostics OBD2 program to the port to check fuel trims, O2 sensor output and MAF output.

I cross referenced the part # on Autozone website, and looks like you've got the right one...

Part Number: 234-9002
Warranty:
3 MO
Application:
With automatic transmission
With California emission
Up-stream sensor (located before catalytic converter)