P0074: Ambient Air Temperature Sensor Circuit A Intermittent/Erratic

What does P0074 mean?

The ambient air temperature sensor A is an NTC thermistor whose resistance falls as temperature rises. Its value is used by the climate control, the outside temperature display and the engine control module, which needs it to enable other diagnostics and to correct its maps. Depending on the vehicle the engine control module reads the sensor directly, or the instrument cluster or another module sends the value over the data bus; some vehicles have no sensor and estimate ambient temperature from intake air temperature. P0074 is set when the signal jumps or is noisy, i.e. changes faster than a real temperature can, which typically points to a loose contact.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Outside temperature display jumps
• Climate control regulates incorrectly
• Check engine light on (manufacturer-dependent)
• Other monitors may not complete

Common causes

• High Loose contact or corrosion at the connector
• Medium Wire broken inside the harness
• Medium Sensor faulty

Likelihood is a general estimate across vehicles; your make and model may differ.