Coolant temperature gauge
I have a problem with my 2003 Audi A6 Avant 1.9 TDI in that the water temperature gauge only works intermittently. It will show the engine water temperature (90°C) on occasion, but will often fall back to its rest position (60°C) after a while. It spends most of its time at rest and, as far as I can judge, is not indicating any temperature. I have changed the thermostat twice, to no avail. The sender, I understand, is at the back of the cylinderhead and is not very accessible on this ‘north south’ engine layout. Any suggestions? Bill Tingle I would first confirm if the problem is a faulty sender unit or a faulty dash gauge. The easiest way to check this is to connect a scanner to the EOBD socket and read off the live data. If the temperature reading on the scanner fluctuates along with the gauge, this will confirm the sender is at fault. However, iif the reading stays steady, the problem is more likely with the gauge or dash connections. If the problem is the ECTS (engine coolant temperature sensor) then this would also affect the running of the engine.
Although the sender is at the back of the engine, it is not too difficult to access. Once the top engine cover has been removed, the connecting plug should be visible. After removing the plug, you can pull out the horseshoe clip holding the sensor in place. A new clip and ‘O’ ring should be fitted with the sensor and I would also recommend using a small amount of silicone lubricant to help the new switch slip into place. The job will be made easier by also removing the air intake hose which runs along the top.
If you do not have a scanner, then the cost of the new sender may be a worthwhile investment, as this is the most common cause of your symptoms.