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Audi A4 1.9 TDi 2002 - Fuel Temperature Sensor #

Posted by Pete Mutlow on April 14, 2013, 6:43 pm

Year of Manufacture *: 2002
Engine Size and Code *: 1.9 TDI
( Optional ) Scanner Used: ACR4 G2

Greetings,

Just finished checking over this car(my wife's) and it popped up with a fault code relating to the Fuel Temp Sensor. The sensor is located near to the fuel filter where I found a broken wire to the connector. Live data (from memory) was reading 40.5 degrees C which I assumed is a default value.

My question is this: Why does the ECU require to know the fuel temperature and what effect does this broken wire have? Car runs fine but fuel consumption has increased over the last few months which I put down to the cold temperature.

Regards

Pete M

Re: Audi A4 - Fuel Temperature Sensor

Posted by Jon Morgan <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3190' width='330' height='300' border=0 style='border:none;'> on April 14, 2013, 10:41 pm, in reply to "Audi A4 - Fuel Temperature Sensor"

Fuel Temperature Sensor G81
The Fuel Temperature Sensor G81 is
located in the fuel return line between the
fuel pump and the fuel cooler. It determines
the current temperature of the fuel at
that point.
The Fuel Temperature Sensor G81 has a
negative temperature coefficient. The
sensor resistance decreases with
increasing fuel temperature.
Signal application
The signal generated by the Fuel
Temperature Sensor G81 is used by
the Diesel Direct Fuel Injection Engine
Control Module J248 to determine
the fuel temperature.
This signal is needed to calculate the
start of injection point and the injection
quantity so that allowance can be made
for the density of the fuel at different
temperatures.
This signal is also used to determine
the timing for switching on the fuel
cooling pump.
Effects of signal failure
In the event of Fuel Temperature Sensor
G81 signal failure, the Diesel Direct Fuel
Injection Engine Control Module J248
calculates a substitute value from the signal
generated by Engine Coolant Temperature
Sensor G62.

Re: Audi A4 - Fuel Temperature Sensor

Posted by Graham Bullock <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2744' width='330' height='300' border=0 style='border:none;'> on April 14, 2013, 10:43 pm, in reply to "Audi A4 - Fuel Temperature Sensor"
Graham Bullock

With a petrol engine it is just the same reason as the ECU needs to know the air temp, the higher the temp the less dense it would be. In the case of hot air you would need less fuel to compensate, but with hot fuel you would need more fuel.

I can only think with the modern diesels that similar applies. I would be interested to know if there is another reason.

Graham

Re: Audi A4 - Fuel Temperature Sensor

Posted by Enda Cosgrave <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3435' width='330' height='300' border=0 style='border:none;'> on April 15, 2013, 9:22 am, in reply to "Re: Audi A4 - Fuel Temperature Sensor"
Enda Cosgrave

Some models use fuel temp to calculate weather the fuel heating element in the filter housing activated in cold weather

Re: Audi A4 - Fuel Temperature Sensor

Posted by Pete Mutlow <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1569' width='330' height='300' border=0 style='border:none;'> on April 18, 2013, 5:13 pm, in reply to "Re: Audi A4 - Fuel Temperature Sensor"
Peter Mutlow

Many thanks for that guys. I have been educated....

regards

Pete M

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