B0040
Outside Temperature Sensor Circuit
The HVAC or body control module has detected an implausible signal from the outside (ambient) temperature sensor. The displayed outside temperature may be wrong or missing and automatic climate control may behave incorrectly.
- Check engine light: Not always
- Emissions related: No
- Repair difficulty: easy
Symptoms
- Warning light or symbol related to the affected system
- Comfort or safety function impaired
Common causes
Ordered by how often each turns out to be the cause.
- Ambient temperature sensor failedCommon
- Wiring or connector fault to sensorPossible
Parts involved
- Outside Temperature Sensor
- Hvac Control Module
- Body Control Module
B0040 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.