118d showing P0036 and P0038 codes (rear O2 sensor)

[Only118d 14]

My F20 118d (2016) is showing P0036 and P0038 codes on my cheap OBDII reader.  

 

Note I didn’t/don’t have a CEL (check engine light) on the dash, I was just checking my OBDII scanner on the car. 

 

So before I blow $200 to $500 on a new O2 sensor does the following make sense or has anyone got any ideas on what else I can check first?

 

As I understand these codes pertain to the post Cat O2 sensor heater circuit. 

So I found the post cat O2 sensor underneath after removing two covers.

I couldn’t see any obvious damage or issues to the sensor, wires or connectors. 

So I thought I would check for continuity of the heater circuit of the O2 sensor as I think this is all you can check for in this case. 

 

However I can’t work out the wiring of the sensor as the wire colours aren’t the usual (they are black, white, grey and red). 

Normally there would be two (2) white wires for the heater circuit. 

I am guessing the heater circuit is the red and white wires based on some searching on the www (and some deduction). 

 

So I continuity (bell) checked between all pins in the O2 sensor connector including between red and white but none appear to be connected. 

 

So I think the heater circuit in the O2 sensor is toast/burnt/broken.  

 

So in summary:

 

1.       I assume the heater circuit for the post Cat O2 sensor isn’t super important or I would get a CEL?   

a.       Although I would still like to fix it. 

 

2.       Does anyone know the colour coding of the O2 sensor wires? 

a.       And what the resistance should be on the heater circuit. 

 

3.       Is there anything else I should check before buying a new O2 sensor? 

 

4.       Does anyone have a good/cheap source for a replacement O2 Sensor?

a.       OEM part number 13628589104 (I think). 

 

5.       Is there anything else I need to consider or check or should i just change out the O2 sensor.  

 

 

 

 

Thanks

 

[kwhelan 241]

clear the codes, they might not come back, lots of bogus faults like that, its only the recurring ones that need attention

[Only118d 14]

On 3/14/2024 at 9:57 AM, kwhelan said:

clear the codes, they might not come back, lots of bogus faults like that, its only the recurring ones that need attention

Thanks kwhelan, I have reset the codes and it comes back repeatedly unfortately.  

[Only118d 14]

So I have ordered a replacement from BMworkshops ($300 + gst).

It will be a week or so before it arrives and I am offline for a couple of months before I can fit it anyway.   

Note the price from CC-BMW was $700 + gst.  

[Palazzo 478]

Have a look at Spareto next time, $170 delivered for a Bosch sensor.

[Only118d 14]

56 minutes ago, Palazzo said:

Have a look at Spareto next time, $170 delivered for a Bosch sensor.

Thanks Palazzo, that is a great price.   I will add Spareto to my "check first for parts"

[Only118d 14]

I finally fixed / replaced the O2 sensor. 

 

The new O2 sensor is the Bosch unit (0 281 004 746) as provided by BMworkshops.

 

Redoing the continuity / bell test across the red and white wires (heating circuit) returned a positive result on the new sensor. 

Where the old unit didn’t so I am sure the heating circuit of the old O2 sensor had broken/burnt out. 

 

So I fitted the new O2 sensor and cleared the ECU fault codes. 

After running the engine there are no more ECU fault codes showing so I am hoping all is fixed now.