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I have a first version MB w168. This car has the MAFs/IATs soldered to the ECU. You can't replace those without replacing the whole ECU. Anyway I have an obd scanner which works with this car and I noticed that the air intake temperature is being reported some degrees below zero while the temperature outside is in the 18/22 C . Is this normal? My understanding is that the car will use more fuel if the ECU thinks the air is cold outside.

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  • This question could certainly be more useful to other readers on the site, it you didn't use so many unexplained abbreviations. Chris, even you can communicate better that this. Okay to use them, AFTER you first explain them. MercedesBenz (MB), OnBoard Diagnostics (OBD), Mass Air Flow Sensor (MAFS)... and so on.
    – zipzit
    Commented Apr 21, 2017 at 20:04

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I'm not a MB expert, but it sure doesn't sound right. The IAT should report fairly close to ambient. That's the whole purpose of the sensor in the first place. If anything it should read a little higher than ambient as the engine warms up and the intake tract becomes heat soaked from the engine bay. This will definitely throw the ECU into the wrong fueling map and cause issues. If it's 20C out and the IAT is reporting below zero, that's a huge disparity.

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  • definitely strange but it could be a problem with the software that is misinterpreting data. I'll check with other testers.
    – Chriz74
    Commented Apr 21, 2017 at 17:38

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