[Nzclive]

Apologies if this is the wrong place for this query, I’ve been trying to avoid a post to ask for help… just stubborn! I have a P0036 o2 sensor heater control circuit sensor 2 fault that I cannot shift. 1k1 Golf. No other faults. Back pressure from the cat seems ok. Car runs great. Have replaced the sensor with another bosch unit and the fault remains. Scanner is telling me the Voltage is 4.5v.
Stumped.

 

[Meirion Rhys]

o2 sensors are typically 4 wire, the heater side is 12v supply and ground, sensor side is typically 5v with reference voltage on the return much like any other sensor like MAF, MAP, CTS and so on.

heater control could be as simple as a fuse blown from damaged wires on a previous sensor, or a control module fault, or damaged loom wiring.

 

[Nzclive]

o2 sensors are typically 4 wire, the heater side is 12v supply and ground, sensor side is typically 5v with reference voltage on the return much like any other sensor like MAF, MAP, CTS and so on.

heater control could be as simple as a fuse blown from damaged wires on a previous sensor, or a control module fault, or damaged loom wiring.

Thanks, I was hoping it was a fuse but I cannot find any reference to a fuse for the o2 sensor. I’m going to test the heater circuit again.

 

[Crasher]

Which part number Bosch sensor did you fit after the cat?

 

[Nzclive]

The part no. Was 03C906262P

 

[Crasher]

That is a VAG number, so it was genuine and your car is DSG. Further than that I would need to look at the wiring diagram at work tomorrow, bank holiday today.

 

[Nzclive]

So I think I’ve narrowed the fault down to the ground wire on the heater circuit. I’m getting 12v on the +ve heater wire but only when I use an engine ground. From what I can tell from research it’s the ground that is switched for the heater circuit. But can I find a fuse or relay associated with the o2 heater circuit… can I #@ll! I found some references to fuse F11, mine didn’t have a fuse there so Ive slapped a 20amp in.. suffice to say I’m clutching at straws now and it made no difference to the fault code.

 

[Crasher]

I need to check at work but yes the heater is ignition live power, ECU earth switched and if the sensor is genuine and definitely not faulty, this is going to be either wiring from the ECU or the ECU itself which does very occasionally happen due to water damage as VW put it in a daft place. I diagnosed one on a 2008 Golf 5 yesterday and it is only the second in about two years.

 

[Nzclive]

Thanks Crasher, I connected the diagnostic scanner up to it again today. On the data stream it’s showing the heater circuit switching rapidly between on and off. Faulty relay? But if so which one is the heater circuit associated with and wouldn’t I be getting other faults?

 

[Crasher]

No relay, ECU direct drive.