Looking to see if anyone has any suggestions, as going a bit mad with an error I am getting causing the EML light to come on in my 2012 Octavia Estate, 1.6TDI, CAYC Engine.

For a while now I have been getting the engine warning light come on, and the error code being reported is P2237 - O2 Sensor Positive Current Control Circuit Open Bank 1 Sensor 1

Things I have tried aiming to resolve this:

• Replaced the Oxygen Sensor - this has made no difference

• Checked the wiring all the way from the connector to the ECU for any damage - none present

• Checked the continuity of the connections from the connector to the ECU (5 wires - all good, no shorts)

• Checked the heater supply - again, no damage, continuity from connector to the engine fuse box

• Checked the heater element resistance - as expected at around 3.5 Ohms

• No shorts between pins on the sensor

• 12V being supplied to the heater element

• Measured the voltage between pins 4 and 6 - these both show 2.5V, and no voltage difference between them

I have looked at the live data (using OBD11 and VCDS and have had the following on a couple of decent length journeys:

Voltage of oxygen sensor bank 1 sensor 1 (broadband sensor) - This starts as a constant '0.503 Lambda / 0.000 V' and after a period of time (that seems to roughly link with the temperature reading increasing) this goes to '0.605 Lambda / 0.000 V

Oxygen sensor 1 bank 1 ceramic temp-TTIP_MES_LS_UP[1] starts at 500, then after a period of time rises to around 830, then settles at a constant 827.1875 for the rest of the journey

Oxygen value calculated-LAMB_EXT_CLC_FIL - This does vary, generally reading between 0.9 and 4, but then does spike up to around 30.

Having checked everything that I can, swapped the sensor, gone back to the original one, checked the wiring etc, i'm at a bit of a loss, and starting to wonder if it might be the ECU at fault rather than the actual sensor and the wiring.

Anyone have any suggestions of what I could check or try to resolve this? Other things to test / check?

Other than the EML light being on the car appears to be running pretty well. Its done 186000 miles, no smoke, not using coolant or oil. Pretty decent fuel economy (getting over 600 miles from a tank of diesel).

Any sign of oiliness within the plug/socket connection of the oxygen sensor?

The reason I ask is from recent frustrating experience of a wideband sensor fault on our Roomster.

Eventually, I found this, which solved it once I had replaced the worst affected bit of wiring and connector on the car loom side. See

https://www.ngkpartfinder.co.uk/assets/Uploads/Sensor-oil-contamination-ver2.pdf

Nope, no sign of any oil contamination - the sensor and the wiring for it is all quite high up in the engine bay so if there was oil there it would be in a right mess!

The oil can come from elsewhere, wicking along in the spaces between wire strands, within insulation; counterintuitively.

Coolant can end up in strange places by the same mechanism.

Just thought it was worth mentioning, cos I had noticed oil in the sensor connectors on mine but hadn't thought it would matter, until I saw that bulletin and found that it really does!

Had another good check a little earlier, and no sign of any sort of liquid present on the loom or the connector to the Oxygen sensor so the hunt for whats going on continues

Long shot but maybe disconnect battery for a few hours and reconnect. Maybe the ecu has had a blip and not coping/recognising new sensor. It should hopefully reset everything and might work. Had similar problems with sensors on my old octavia. As a last resort I disconnected battery, left it overnight and reconnected and it seemed to cure itsef.

Alasdair