1275 Code on 2001 Boxter S (closed loop issue)

[adrianw]

Hi,

The car has been logging codes (1275 & 1128) for a bit which I had thought might be to do with there being no bolts left where the header meets the rest of the exhaust system.

I got the bolts sorted and replaced an Oxygen sensor on Bank 2 as it had been rubbing off the auto box and the insulation was a bit thread bear. So I thought I had a solution for each code.

But now I am still getting this 1275 Ageing sensor code.

When the engine is running I can see the other three 02 sensors cycling as you might expect but Bank 1 sensor 2 as my OBD Wiz software calls it is sitting at about 0.07 mv, where the others are 0.1 to 0.8 mv.

So it looks dead.

But - If I switch on the ignition and leave it for a minute all the O2 sensor values settle down to 0.44 mv (I think the manual suggests 0.45mv?).

When I start the engine the suspect 02 sensor behaves like all the others until the engine goes closed-loop - then it fluctuates below 0.1 mv.

The local specialist wants to get an auto electrician in - but I am thinking that the sensor is behaving and that it might actually be giving a correct value as it senses it.

Thoughts?

Cheers

Adrian

[adrianw]

[adrianw]

I forgot to say that we swapped this O2 sensor for a new Bosch Part and it gave the same readings which made the specialist think it was an electrical issue.

But the fact it seems to behave in Open-Loop makes me wonder.

[adrianw]

Hi,

I've been doing a bit more back ground reading and I wanted to confirm that bank 1 sensor 2 is the post cat sensor used to check the cat is working as expected.

What might this sub 0.1mv value post cat say about the cat?

Is (<0.1mv) too 'out-of-range' or could it mean there is too much oxygen coming from the cat?

Cheers

Adrian

[adrianw]

Hi,

I was reading the Pelican article about vacuum leaks and the trick about taking the oil cap off to check for effect.

So I connected the OBDWiz from cold turned on ingnition and all four sensors are showing 0.45mv.

Start the engine, all four start to fluctuate in Open loop, car moves to closed loop Bank 1 Sensor 2 flatlines below 0.1mv.

So I take the cap oil cap off and the engine immediatly starts to run much rougher.

After a few moments the Bank 1 Sensor 2 recovers and starts showing values > 0.1mv.

What's going on there?

Cheers

Adrian

[adrianw]

Hi,

Anyone know what to do with the "oxygen sensor test harness" described on Page 97-12 of the Bentley Service manual?

It is a connector on the bottom of rely panel 2, just under relay 10

Cheers

Adrian

[mikefocke]

How the sensors should work is described here https://sites.google.com/site/mikefocke2/oxygensensors.

[adrianw]

Hi
After time with a specialist independent and then Porshe with no diagnisis from either I asked my local garage to smoke test the exhaust.

I had asked both the independant and porsche to try this but they both neglected to do so.

So now i know i have a cracked catalyst.

Why are garages so keen to avoid smoke testing?

At least this thread has closure now.