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Ambient Air Temperature Sensor (Used for engine management?)
Can anyone confirm if the Ambient Air Temperature Sensor is used for engine management? Not IAT, the one that shows outside temp on your dash.
I have mine unplugged and tossed the sensor in the trash since I don't need it on a track only car. and it does actually throw a CEL when unplugged --> P2070 The outside temperature sensor has a short circuit to ground.
I was picking up some parts at the dealership and shot over to service to see if they'd do custom coding (big nope) and the SA seems to think the sensor is actually used. At least for the turbo cars it apparently is he wasn't certain about the M156 platform. Maybe it's used for SAI or AC operation which I also have removed.
Can anyone confirm if the Ambient Air Temperature Sensor is used for engine management? Not IAT, the one that shows outside temp on your dash.
I have mine unplugged and tossed the sensor in the trash since I don't need it on a track only car. and it does actually throw a CEL when unplugged --> P2070 The outside temperature sensor has a short circuit to ground.
I was picking up some parts at the dealership and shot over to service to see if they'd do custom coding (big nope) and the SA seems to think the sensor is actually used. At least for the turbo cars it apparently is he wasn't certain about the M156 platform. Maybe it's used for SAI or AC operation which I also have removed.
@Jasonoff Is it possible to “code” the sensor out by installing a resistor in the harness connector? Assuming you haven’t cut the connector off the harness. Do you still have the sensor to measure resistance?
Doubtful it is actually used as ambient temperature is not required for any sort of engine management. It would be part of the hvac system for certain.
As you'll find, it is better to leave all sensors attached and working if you're continuing to use the stock ecu, track car or not. Once you have gone to a standalone you can get rid of any redundant wiring harness to save weight and complexity. for now, there is no reason to toss random sensors tbh.
Doubtful it is actually used as ambient temperature is not required for any sort of engine management. It would be part of the hvac system for certain.
As you'll find, it is better to leave all sensors attached and working if you're continuing to use the stock ecu, track car or not. Once you have gone to a standalone you can get rid of any redundant wiring harness to save weight and complexity. for now, there is no reason to toss random sensors tbh.
My brake cooling duct took over the sensor location. Wouldn't have thought an outside temp display sensor would throw a code.
I also removed my washer fluid reservoir. No code with the level sensor removed. You saying I should put it back in?
Do the turbo cars use the same ECU? Could by why that sensor is associated with the engine computer and why it would throw a CEL when unplugged even though it's not used on our platform.
I read a lengthy document in WIS sometime ago. I remember the M156 has 3 temperature sensors:
1- The MAF sensor has a temp sensor, but it is ignored by the ECU.
2- The intake manifold has the IAT sensor which I believe is the one used for engine management.
3- The front ambient temp sensor is used by the SAM unit for HVAC operation.
I find it strange that sensor #3 throws a code when unplugged. Perhaps it can be used by the ECU in case sensor #2 fails.
Sorry gents I can't find a pic, what's the standard location for this? I have it hanging near the horn/secondary air pump
I literally just learned about this while my bumper was off this past weekend and forgot to plug is back in. It lightly snaps in at a certain angle behind the grill.
2004 E55 AMG, 2006 CLS63, 2004 ML55, 2014 E350 sport
If you disconnect it you'll find you get a engine check light... or atleast a fault code in the ENGINE ecu.
That alone is enough to tell me it probably is related to how the engine runs IE what its expecting to see air temp wise going into the engine/across the mafs.
These things are kinda touchy I just had to clean my mafs with maf cleaner to get rid of a couple of other maf related codes aswell as fix the wiring on the temp sensor above which is why I know.
Last edited by austingtir; Sep 12, 2023 at 01:01 AM.
Our cars use it for HVAC as well. But nothing engine management related.
Originally Posted by austingtir
If you disconnect it you'll find you get a engine check light... or atleast a fault code in the ENGINE ecu.
That alone is enough to tell me it probably is related to how the engine runs IE what its expecting to see air temp wise going into the engine/across the mafs.
These things are kinda touchy I just had to clean my mafs with maf cleaner to get rid of a couple of other maf related codes aswell as fix the wiring on the temp sensor above which is why I know.
It's used for the HVAC system which is why it will throw a code. It's not used for engine management on this platform.
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12' W204 C63 AMG coupe "T-Rex", 12' W451 Smart Fortwo Pulse (99' W202 C43 AMG + Ultima Can-Am sold)
Yeah, understandable that it's used for the HEVAC system, but can't see it having any relation to engine management. That would come from the MAF I would imagine.
this sensor is ONLY used as ambient temp sensor for the ECU (ancillary use) and Dash Cluster.
the temperature sensor for the engine computer and the engine operation is built into the MAF sensor like it is for all vehicles that utilize a MAF sensor.
@Jasonoff Is it possible to “code” the sensor out by installing a resistor in the harness connector? Assuming you haven’t cut the connector off the harness. Do you still have the sensor to measure resistance?
You need the sensor on the automatic or you get horrible shifting when cold. Cold start program like choke on old cars won't run long enough if your temperature senser if faulty
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Ambient Air Temperature Sensor (Used for engine management?)
Ok... don' remove any sensor that makes the ecu happy.
