Hi, on my 51 plate bug the front lambda sensor system is giving a problem, the sensor is fine (ive changed it out for one i know works) the problem is that there is 12v live for the heater, no probs there. But there is a constant reading of 3.7v on all other wires, the two earths and the signal, anyone else came accross this problem? also any ideas? thanks in advance

 

Are you taking the voltage with the engine running? i cant remember of hand but i think it should be about half a volt variable but will check.Below is a manual that gives you a detailed way of testing.
http://cgi.ebay.co.uk/Subaru-Impreza...item35b198b47c

 

With the engine running you should get about 0.1v to 0.8v to check the earths check terminals 8 and 9 on your ecm/ecu

 

Yeah mate, the sensor voltage is fine, ive got a bigger problem as said the voltage from the ecu is 3.7 on all wires (two earths and signal) this is measured under the bonnet with the lambda sensor unplugged. I will pin out the wire back to the ecu to check for a break later, but i cant see that being the problem if there is voltage at all three? prehaps there is a burnt/corroded track in the ecu? any one else had a similar problem?

 

There shouldnt be power on terminal 1 of the sensor according to the manual this should be a earth fed from the ecu terminal 8/9. Sensor terminal 2 is the heater which is ok,terminal 3 is the - signal which shows 2.4 to2.7v going to ecu pin 29,and teminal 4 is the + signal which shows 2.8 to 3.2v going to ecu pin 19.God knows why theres power coming of your ecu pin 8/9 but the rest looks ok.

 

so now you see my problem could be a broken/burnt/corroded track in the ecu, ill have to open it and have a look

 

Sorry got a bit confused when you said a problem with the signal and 2 earths,what you meant was 1 earth and 2 signal As there is only one earth at least it halfs the problem id disconnect from the ecu and see if the wires are shorting across first.

 

there is four wires mate, a 12v live for the heater, and an earth for it (earths through the ecu) also there is a signal wire from the lambda to ecu and another earth for the signal circuit that goes to the ecu. Ill have a poke around and see what i can find. The only wire that is good is the 12v live, shows 14v when the engine is running, which is spot on, the rest seem to be floating around 3.7, which looks like an ecu voltage to me.

 

Emmisions problem fixed, passes on fast idle and idle now, thanks for the help