mekelly

I own a 2002 LS430. Check engine light came on, scanned code P0135. That code indicates a bad o2 sensor heater circuit on bank 1, sensor 1.

I replaced the o2 sensor yesterday and cleared the code. I drove the car yesterday afternoon and the check engine light stayed off. Looks like a successful repair!

Unfortunately, when I started the car today, the check engine light came on again and I scanned the same code, P0135.

What else should I check? Has anyone got the relevant page(s) from the service manual? Continuity and/or voltage printouts for the connector and sensor?

Is there a fuse (or relay) that supply's power to the o2 heater circuit?

Thannks in advance!

rkw77080

The 2003 LS430 Repair Manual (also applicable for 2002) does not mention P0135, so I'm not sure what it is for.

The B1S1 O2 sensor can trigger 3 DTCs, 2 for the heater circuit (P0031, P0032) and another for the sensor circuit (P0134).

mekelly

Thanks for the files! Not sure why P0135 isn't listed. It's an Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1).

When the ECM determines that the sensor hasn't heated up quickly enough it sets the code. I dd check continuity between the 2 ground (black) wires on the old sensor and they're open so it does appear the old sensor is bad. Unfortunately, I didn't check the new sensor before I installed it.

Very curious!

rkw77080

You're welcome. Here are a few more pages on O2 sensors...

mekelly

I hooked my scanner back up to the car and it's not showing any voltage coming from the new sensor.
Although the new sensor could be defective, I have a bad feeling there's something wrong with the wiring harness and/or connector.

I checked the old sensor and the built-in heater circuit was definitely bad. The circuit was open and should test between 11-16 ohms (thanks RKW77080).

I purchased a new Denso sensor and tested it before installation! The heater circuit reads within spec.

So my plan is to undo the sensor connector and test the heater circuit on the installed sensor to see if it was DOA when I received it. I'll also try to check that I am getting 12V through the wiring harness to the connector.

Hopefully that checks out and it's just a bad sensor, otherwise I have no idea how you'd repair that harness and connector, there's just no room (or enough excess wire) to do anything!

coug66

I have the exact same code. My car side plug came loose exposing the 4 wires. I pulled it and the oil sensor wires up above the valve covers then soldered extension wires.