P1276 even after sensor changed - showing 0 resistance

[4StringBass]

Hi,

We recently got P1276 "Fault Code 22, signal delay time for oxygen sensor ageing, bank 2".

 

The sensor got replaced and within 50 miles it had thrown the same fault code again.  I reset it, and it was 100 miles before it tripped the CEL this time.

 

Hooked the Durametric up and went for a drive.  There is no resistance showing on the bank 2 plug (see attached image).  Everything else was roughly the same for bank 1 and bank 2 as we were driving.

 

I have done a continuity test between DME pin 30 and the oxygen sensor relay pin 87 as per the workshop manual for both sides of the car, with one sensor unplugged each time and it seems OK, it's not an open circuit.  There is approx the same resistance in the heater circuit of both pre-cat sensors when measured from the sensor plug.

 

What other resistance in the system looking for?

 

What can I check next?

 

I'd rather eliminate everything before throwing another sensor at it.

 

Thanks in advance!

[Ahsai]

You can try this.

- Unplug the bank 2 pre-cat sensor

- Check if the pin with the black wire has +12v with key ON engine OFF. That's the power supply to the heater of the O2 sensor.

- Check continuity between DME pin 30 and the pin with the red/white wire on the O2 sensor socket.

[4StringBass]

@Ahsai, thanks for your reply.

 

Yes, 12V power to the black wire.

 

I have made a mistake in reading the DME pin 30 to relay, as I was using the 97-99 wiring diagram to figure out the DME and I've actually just been measuring an earth connection 😩

Does anyone have the DME pin out for a 2002 Boxster S?  Part number 996.618.605.00?

 

[Ahsai]

Ah, your's is DME 7.2 so it has 5 plugs on the DME.

 

Since you have Durametric, you can plot the O2 sensor voltages of all the 4 sensors. After engine warm up and at idle, you should see the precat voltage swing between ~0.2v to 0.9v about once a second. The postcat voltage should remain close to 0.6~0.7v steady.

 

This P1276 code is complaining about the switching delay of the sensor (between lean and rich). If you have a regular scanner that reads mode 5, you can also see the O2 sensor test results that will give you more clues.

 

Is the replaced sensor Bosch and the model correct?

[4StringBass]

On ‎6‎/‎20‎/‎2019 at 5:48 PM, Ahsai said:

Ah, your's is DME 7.2 so it has 5 plugs on the DME.

 

Since you have Durametric, you can plot the O2 sensor voltages of all the 4 sensors. After engine warm up and at idle, you should see the precat voltage swing between ~0.2v to 0.9v about once a second. The postcat voltage should remain close to 0.6~0.7v steady.

 

This P1276 code is complaining about the switching delay of the sensor (between lean and rich). If you have a regular scanner that reads mode 5, you can also see the O2 sensor test results that will give you more clues.

 

Is the replaced sensor Bosch and the model correct?

@Ahsai, you're a legend.  It's the rear sensor reading a tenth of what it should be.

 

Thanks again.