External air temperature sensor

longdog

longdog

Member
1.4 tdi BHC. Is the external air temperature reading, as measured by the sensor in front of the radiator, fed to the ECU, for instance in such a way as to affect fuelling or timing? Or is it solely for the purpose of display on the dashboard?

Many thanks.
 
Many thanks, Audifan. Fuel consumption is a little higher than that of my previous (AMF) A2, and starting is sometimes a little slow. Outside air temperature readings on the instrument panel are erratic and often very wrong. I have read several previous threads on failing external temperature sensors, but nowhere did I pick up that they could affect starting or consumption. Obviously I need to replace mine, and not just because I'm getting the wrong reading in the cabin.
 
Make sure the rest of the systems are good. How old is the air filter? How old is the fuel filter? Are there any leaks from the filter housing? Are the fuel pipes in good order, tight and not porous? Is the tandem pump failing? Does the car start better if parked pointing down hill? Is the ASV working correctly? Is the injector loom too old or intermittent? Are the injectors and seals good? No vacuum leaks? Glow plugs good? Water in the fuel?


You get the picture many items could cause those issues. Perhaps you are driving it differently? How are you measuring your fuel consumption?

Could even be a difference in the fuel stations pumps or different fuel. ECU remapped?
 
I second everything Graham has asked above - and add - are the tyres / pressures / wheels exactly the same as your AMF?
Quite apart from the external air temp sensors, how about the fuel temp sensor and the coolant temp sensor? You mention the erratic exterior temperature reading on the dashboard , but don't comment on coolant temperature (so reading between the lines this is deemed accurate) - but I'm also guessing you're going by the dashboard readings rather than an OBD2 reader or VCDS to check that the ECU coolant temperature channel is reading the same as the dashboard display.

Reason for asking this is that the coolant temp sensor has 4 pins and sends two independent temperature readings - one to the ECU, and one to the dashboard. They should be the same / near-identical, but if the sensor is older, it is plausible that one channel may have failed, and if it is the ECU side, this would only be evident by poor fuel consumption while the dashboard display is normal - effectively the ECU would be running blind as far as temp is concerned and it is like driving with the choke fully out (in old money!). Finally - is the thermostat in good condition?
 
And that was not even considering binding brakes, alternator load, using climate control more, poor battery, bad earths or wiring, higher spec and heavier car, etc

To rule in or out something that is detected as a fault ( not everything does ) then I suggest you get the car scanned with a very good scanner and come back with the results
 
My thanks to all who have responded, and particularly to Spike for answering the original question. It is clear that the ECU takes air temperature from the intake manifold temperature sensor G72 and that for glow plug operation it is taken from the coolant temperature sender G62.

Any diesel owner should read SSP 223 if they haven't already done so - the complexity of what is going on under the bonnet is truly astonishing.
 
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