I have got a code 21 on my ST205 WRC so replaced the lamda sensor but when I came to clear the memory I still kept getting code 21. I checked all the wiring for continuity which was fine. I am now completely baffled as to what the problem is. I also checked resistance of the wire but that was ok. Any help would be appreciated. Thanks

Sent from the middle of nowhere

You need to reset the ECU by pulling the 15A fuse to clear any error codes.
All explained here on Kris and Loosey's site - http://www.gtfours.co.uk/

Go to:
How to > Check Error Codes > ECU ST205
Check for 205 ECU Error Codes

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Yep did all that ranging from pulling the fuse, taking the battery off to completely to removing the ECU completely while checking the wiring. Still got the error code!

Stick a meter or test lamp across the two white wires inn the connector and make sure you have power with the ignition on

If it shows an O2 sensor code immediately without even starting the engine then I would expect it be lack of heater current.

As Steve says, this is the 2 white wires. One should be fed from the 12V ECU supply (live when on, check relative to engine earth) and the other should be pulled down to earth by the ECU to switch on the heater.
With ign on - if neither white is at +12 relative to engine earth then the problem lies in the 12V feed to it. If both are at +12 then there is a problem with the ECU or the link from ECU to sensor.
If one is at +12 and the other at ground, then unplug the sensor and check continuity between the 2 whites as the sensor may be duff.

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Hi Guys. Bit of an update. First of all my heater wires are black not white, the ground is white.



In the diagram pin 2 is 12v with power on. Pin 4 is earth (tested). With power on voltage between pin 1 & pin 2 is between 2.5v and 3v with the engine warmish, having stood for half an hour after driving home from work. I have just put a brand new sensor in. I'm not quite sure what these figures mean especially the voltage between 1 and 2 which seems to be moving.
Any help really appreciated