Cause
Faulty ambient air temperature sensor
The sensor measuring outside air temperature, drifted or failed. It does more than feed the dashboard display: the module uses it as the reference against which other temperature sensors are judged, and it informs air conditioning strategy, intake temperature correction and cold-start behaviour.
Position causes more faults here than failure does. These sit behind the grille or in a door mirror, and a sensor in radiator heat reads high whenever the car is stationary — which is why many vehicles freeze the displayed value below a certain speed and only update it once air is moving. A reading that is high in traffic and correct once moving is that behaviour, not a fault.
Its role as a reference is what makes a drifted one expensive to misdiagnose. A correlation code between two sensors names a disagreement without saying which is wrong, and if this is the one that drifted, the other sensor gets replaced for nothing. The cold soak settles it: after a night standing, every temperature sensor on the vehicle should read close to this one and to each other.
Mirror-mounted sensors fail from water ingress and from careless glass replacement, which is worth asking about where one has been changed.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (6)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0070 Ambient Air Temperature Sensor Circuit A Likely for this code Low
- P0071 Ambient Air Temperature Sensor Circuit A Range/Performance Likely for this code Low
- P0072 Ambient Air Temperature Sensor Circuit A Low Likely for this code Low
- P0073 Ambient Air Temperature Sensor Circuit A High Likely for this code Low
- P009A Intake Air Temperature/Ambient Air Temperature Correlation Likely for this code Moderate
- P0074 Ambient Air Temperature Sensor Circuit A Intermittent/Erratic Low
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