Don't forget you've got two circuits to test for on the sensor or plug, heater circuit 12v and a earth switched through the ecu, then the emissions side signal and earth, your code is suggesting heater side. did you erase the old codes,

 

Yeah I erased it and it came straight back up, and we had the live data displayed on the snap on data reader computer.

 

Coil pack failing?

 

Right, I came home from work and put a genuine secondary 02 sensor in, same fault code. It's sat at a constant 3.8 volts. Anybody come across a common problem or wiring faults?

Cheers, Edd

 

So its not jumping about anymore then? I guess that is step forward.

I think you are starting to get into the realms of needing an electrician on this, electrical problems are so hard to diagnose without actually being there. Mostly because electricity is all magic.

Dodgy earth?

 

First thing is to check that your scanner is erasing the code, some scanners don't on the pre 2000, then as you have a code for the heater circuit you need to get the wiring diagram for the 02 sensors from the workshop manual and trace the 12v heater feed from the fuse box to the sensor, then trace the earth back to the ECU, the 12v will feed both front and rear sensor and go through a couple of connections, the earth will be separate for front and rear, reading the signal won't tell you if the heater is working, it's unusual for half the sensor to be missing was it melted or broken,

 

So I'm guessing its not a common fault?
Yeah the codes are being erased, but coming back. I don't know about the sensor, it was just missing the end, probs broke off for one reason or another.
I've purchased a workshop manual so I'll dig through that and check the wires and report back.

The other thing I'm thinking is that when the old sensor broke it perhaps shorted and damaged the ECU.
Is the ECU coded to the car or can I bung another one in?

Cheers!

 

When you get the manual You may find that the 12v feed for the front and rear sensor start off from the fuse then split at one of the connectors so you will have to check if they have a feed at each sensor plug, if it shorted it should have blown the fuse and both sensors will have no heaters