Is it essential.....
 

that the heater on the lambda is wired in??? its the heater that has shorted and causing my problems, as long as its not shorted to the signal wire too.

Just means it will take longer to get up to temp and the o2 reading will be poor until engine hot. Is likely to fail mot. A new universal one is only about 40 quid.

They normally go open circuit. Difficult to understand how it could go short circuit, as only a heater element, it the controlled short that generates the heat

What were the running symptoms that caused u to start looking at this

The problem originally was that the 10v feed to the idle air valve and the purge solenoid was present at the plug behind the battery, but as soon as the engine loom was plugged in it went away. I tested the engine loom, and stripped it and it was fine. i tested the plug and the 10v feed was continuous with the earth from the ecu and lambda sensor.
At the time i didnt realise that the earth was also the earth from the lambda, so i stripped out the dash, stripped the loom right back and tested everything, of course, it was all ok, bar the main relay, which is melted, its dead.
i had continuity between the 10v output from the main relay and the 10v feed to the engine loom, which is right, i also had continuity between the 10v to the engine loom and the earth from the ecu/lambda.
What i discovered, is that the ecu, lambda, all the sensors earth through that loom onto the engine, so when the loom was unplugged, i had the 10v, but as soon as i plugged it in, i made the earth connection, shorting the circuit out, and losing the 10v.

I checked the wiring diagram again, and found the lambda link, which i missed before.
I only unplugged it to settle a niggle in my mind, and as soon as i unplugged it, the short went away, no continuity between the earth and power, everything is as it should be within the loom with the lambda unplugged.
Plug the lambda in, the short re appears.

That is why i think its the lambda.


The problem originally, well there wasnt a running problem at all, that was kinda the issue.
There was some 'creative' wiring to circumvent this issue, so he could sell the car.
he had tapped at 12v from the battery feed INTO the 10v feed on the engine loom. this gave me a 1.5amp battery drain.
it was investigating this issue that i decided that the problem needs fixing, backing 12v up through the loom back to the main relay is never a good idea, and has melted the relay.

Today wasnt a total waste of time, at least i know that the loom is not melted behind the dash.

My last 4 cars have all failed on emissions. i leave the car with him for 10 minutes and he works his magic!!

You may find that 10V from the heater of the negative side of the lambda is correct, when unplugged.
As mentioned it is only a heater element (effectively a resistor), so if you connect a voltmeter between it and ground I would expect to see a voltage.

I tested it today, its definately failed short. i cut the wires for now, will replace it when i can.

What impedance did it measure

i used the continuity tester on the multi, it measured 005 when tested across the heater.