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Discussion Starter · #1 ·
The O2 sensor Bank 1 Sensor 2 on my Trajet 2 ltr GSI shows a heater circuit malfunction. Everything else is ok and the car runs perfectly. Clearing the fault works until I switch the engine off. When I start it up again the code shows and the EMS light comes on again. I have to assume the sensor is faulty. Which one of the two on the exhaust down pipe is it? The top or bottom one? Am I right in guessing it is the bottom one?
 

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Which one of the two on the exhaust down pipe is it? The top or bottom one? Am I right in guessing it is the bottom one?
Should be. Numbering is downstream. #1 pre cat (feedback sensor for fuel trim), #2 post (monitor sensor for cat efficiency)
 

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Discussion Starter · #5 ·
Have done that. The fuse is ok. Puzzling that the values are ok as well. Mostly under 0.45 V and during acceleration going up to 0.75 V, occasionally 0.9 V. So the values indicate the sensor works ok and the wiring appears to be ok as well. Fuel consumption is pretty normal as well. So the big question is - what is it?
 

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The heater is a separate circuit in the O2. It is used to heat up the O2 faster when you first start the engine. It could be the wire going to the O2 or the O2 heater itself. If you are handy with a voltmeter and can get to the plug it's pretty easy to check.
 

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Discussion Starter · #7 ·
Thanks, RR, never thought of that and will have a look at that. I just couldn't see the logic when all values show the sensor seems to be working.
 

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There should be 5V and 12V at the plug. The 12v is for the heater. The 3 wire O2s share the ground, the 4 wire O2s don't with two ground wires and a 5 wire O2 is a Wide Band O2 capable of reading AFR outside the 14v +-1v range.
 
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