A3 1.6 54 plate

[goose0709]

Hi Hopefully someone will be able to give me some guidance.

I have carried out a cambelt change on the above vehicle and the EML has come on afterwards. Thinking there was something wrong with the timing I have checked and re-checked this and all is good.

Scanning the car shows code 17524 - Oxygen (Lambda) sensor heating bank 1 sensor 1 - Open circuit. I have printed the test procedure off Autodata and followed that. All seems to be ok apart from the supply voltage for the heater which Autodata is saying should be between 11 & 14 volts. It is a constant 4.1 volts.

Can you advise what controls this supply voltage? Is it direct from the ECU or via a fuse in the fuse box.

I have been in this car for a LONG time and would like to get it sorted please...

Many thanks for any help or advice you can give

Jason

 

[bearthebruce]

How did you measure the voltage? If memory serves, one side of the heater is at battery voltage and the other side is switched by the controller to ground. So, if you measured the voltage across the two pins at the sensor, then what you measured is possible.. What I am saying is that if you have a broken wire from the controller to the sensor - or possibly a poor connection, the current required to run the heater cannot flow and the voltage across the heater will not be what is expected because not enough current is flowing through it. You could have a bad ground for the sensor circuit... you could have a bad output on the controller.... Controllers are expensive so I spend my time trying to figure out if I had bad connection or broken wire before I'd ever suspect the controller itself.

 

[goose0709]

Thanks for the info. I measured the voltage as detailed on Autodata between pin 3 on the sensor multiplug (mounted on a bracket on the bulkhead) and earth. This measured a constant voltage of 4.1 volts. I then got a collegue to crank the engine and should (according to Autodata) have seen a voltage of between 11v & 14v. The voltage fluctuated between 4.08v & 4.1v but did not go any higher.

 

[bearthebruce]

The earth connection was the minus terminal of the battery? Without a wiring diagram in front of me for your car, I'm not going to be much more help.

The +side of the sensor is controlled by a relay. If that was not at +12, then you need to trace that wire. If the control side heater element is not switching fully to ground or close to it, then there is something wrong on that side.

I am trying to get some information from a wiring diagram to try to help you.

 

[goose0709]

ruce this information is great as it gives me a guidance on where to go next. Yes the earth was the negative connection on the battery.

I will start to have a look to see if I can trace this wire to the relay that controls it.

Many thanks

Jason

 

[goose0709]

Found the problem to be missing fuses. Someone looked at the car before me for a problem with the rear wiper and 'solved' the problem by changing fuses. unfortunately to get to the solution they pulled out various fuses and forgot where they went!

Found 2 fuses missing. Replaced them and cleared the codes and nothing came back on.

Thanks for the assistance

Jason

 

[bearthebruce]

Nice - that 12 volt on the other side of the heater is a needed thing! Glad you got it sorted. I was going to post a wiring diagram snap shot to get ya started. It was not from your car - but a generic representation. In it you could see the typical wiring. In any event, glad you found the issue.