I've got a 2002 A6 with the 2.7t. In the last few months, the check engine light has been coming on, staying on for weeks, then turning itself off for a day or two, before coming on again. I took the car to my mechanic and he showed the car had a P1296 fault code. The scanner showed that the coolant temp would sometimes drop to -40F for a second, then go back to normal. He changed the coolant temperature sensor with the correct replacement part (oem green sensor). The next day the check engine light was on again, same code, so I ordered another sensor from Audi, gave it to the mechanic and had him put it in. The next day, the check engine light was on again. Does anyone have any suggestions on this one?

 

Flush you radiator and cooling system. Replace the coolant to AUDI specs. See if this change trips any faults.

 

Could old/out of spec coolant cause the coolant temperature sensor to read -40f momentarily?

 

Old fluid filled with dirt and gunk coul have an effect. This step is more about preventative maintenance, but could be a root cause for the innacurrate readings.

 

Thanks prbayha, I'll do it. Another thing that may come into play is that my wife usually notices the check engine light on her way to work. She works about 3 miles from the house, so the engine literally never warms up to normal operating temperature. When the check engine light turns off by itself, it's usually when I'm driving it on a long road trip, while the engine has been running for hours on the highway.

 

Is there only 1 coolant temp sensor on the 2.7t?

 

Just one other thing you might check is all the connections between the sensor and the computer. You might look for loose or corroded connections. In my mind if the sensor bounces quickly between -40 and normal temp that really sounds like some problem with the connection. It could even be a problem in the computer itself.

Just a thought, I had a Infinity that registered an O2 sensor that was bad but it turned out to be a grounding problem with the sensor and not the sensor itself. Fortunately I had a manual that told me to check that first so it saved me time an money.

 

Where can I find where the sensors connect to the computer? I just got the car back from the shop. On my way to work this morning, the check engine light came on again. I havent pulled the code, but I'm sure it's 1296 again. It's got to be a bad wire, or loose connection somewhere. My mecanic told me he wiggled the sensor connector and cables with the scanner hooked up and found no jump in readings.