Camshaft sensor/Oxygen sensor shortcircuit

[Fred Byrne]

I cannot find the short circuit that causes the F3 fuse to blow. I replace the fuse car started and off I go. Get home switch engine off but it won't restart. The Fuse 3 blown again. I suspect the rear Oxygen sensor so I unplug it and no short circuit anymore. My question can a failure in the sensor heater element go short circuit? I would have expected an open circuit. The cam sensor and both oxygen sensors are the only components on this circuit. I have wiggled and pulled the relevant wires but all seems OK.

Any theories anybody?

Fred

[SD1too]

Originally Posted by Fred Byrne

I suspect the rear Oxygen sensor so I unplug it and no short circuit anymore.

Renew the sensor Fred. You've found the fault.

Simon

[Fred Byrne]

Hope so. New one arrives Tuesday. MOT Wednesday. Is it an MOT failure if sensor fails to arrive on time? There is no engine warning light so might get away with it.

Thank you once again!!

Fred

[SD1too]

Originally Posted by Fred Byrne

Is it an MOT failure if sensor fails to arrive on time? There is no engine warning light so might get away with it.

Hi Fred,

If the tester stops the engine and it won't restart because the fuse has blown then he won't be able to complete the test. Whether the current certificate expires on Wednesday or later is immaterial as you can still take the car home for repair and submit it for a pre-booked test at a later date.

I don't believe that you'll have a problem with the emissions measurements because that's carried out at normal running temperature so the lambda sensor's heater fault is irrelevant.

Simon

[Fred Byrne]

That's very interesting. I hadn't realised that the heater was irrelevant at running temperature. I think the restarting problem seems to have been resolved. I'll check the oxygen content of the exhaust gases. The working sensor seems to keep its level at about 3% which is satisfactory but it of course is on the pipe at the front of the car i.e. cylinders 1,3 and 5.
Fred

[dave lincs]

Fred the wiring on the sensor will have chafed through on the heat shield just up from where it screws into the front pipe

Dave

[Fred Byrne]

I'll check that today.

Thanks
Fred

[Fred Byrne]

I have checked the wiring. The sleeve on the 2,4,6 cylinder side had chafed but had not damaged the actual wires. The sensor on the 1,3,5 exhaust had no damage to the wiring but was giving erratic readings. I disconnected it at the plug. I measured the resistance between the various terminals. There was 6 Ohms between pins 4 and 3. I would have expected the heater element to be connected between 12 volts and earth. That of course is just a guess/supposition. There was high resistance between all the other pins.

I then switched the ignition on and measured the voltage at all 4 pins on the socket on the vehicle wiring side( sensor unconnected). Pin 4 colour y/g had 12.4 volts, Pin 3 Blue/brown had 3.8 volts, Pin 2 black 0.0 V, and Pin 1 Blue/yellow was .4 volts.

I'll repair the damage to the sleeving and as the diagnostic reader read a fault of heater failure on that sensor I shall replace it tomorrow and see what happens.

Fred.

[SD1too]

Originally Posted by Fred Byrne

... (sensor unconnected). Pin 4 colour y/g had 12.4 volts, Pin 3 Blue/brown had 3.8 volts, Pin 2 black 0.0 V, and Pin 1 Blue/yellow was .4 volts.

Hi Fred,

I thought that you might like to know what those pins do.

Pin 1 is the lambda sensor output to the ECM, pin 2 is the heater earth via the ECM, pin 3 appears to be the sensor earth (twisted pair with pin 1) and pin 4 is the ignition controlled supply to the heater.

RAVE gives the resistance of the sensor heating element (pins 4 & 2, sensor disconnected from loom) as 6Ω at 20˚C. That's useful data!

Simon

[dave lincs]

Originally Posted by Fred Byrne

I have checked the wiring. The sleeve on the 2,4,6 cylinder side had chafed but had not damaged the actual wires. The sensor on the 1,3,5 exhaust had no damage to the wiring but was giving erratic readings. I disconnected it at the plug. I measured the resistance between the various terminals. There was 6 Ohms between pins 4 and 3. I would have expected the heater element to be connected between 12 volts and earth. That of course is just a guess/supposition. There was high resistance between all the other pins.

I then switched the ignition on and measured the voltage at all 4 pins on the socket on the vehicle wiring side( sensor unconnected). Pin 4 colour y/g had 12.4 volts, Pin 3 Blue/brown had 3.8 volts, Pin 2 black 0.0 V, and Pin 1 Blue/yellow was .4 volts.

I'll repair the damage to the sleeving and as the diagnostic reader read a fault of heater failure on that sensor I shall replace it tomorrow and see what happens.

Fred.

If you need a sensor let me know as I have got some