Electrical and sensors

P0074 — Ambient Air Temperature Sensor Circuit Intermittent

Severity: low Safe to drive

What P0074 means

The PCM constantly reads the voltage from the ambient air temperature sensor, which should change smoothly with outside temperature. P0074 is stored when that signal drops out, jumps around or goes out of range for short periods. The usual culprit is a poor connection or damaged wiring, and less often the sensor itself.

Symptoms

  • Check engine light on
  • Erratic or unrealistic outside temperature display
  • Climate control not behaving correctly
  • Temperature reading that comes and goes on the dash
  • Rarely, slight idle fluctuation or a harder cold start

Possible causes

  1. Loose, corroded or damaged sensor connector
  2. Chafed or broken wire in the sensor circuit
  3. Failed ambient air temperature sensor
  4. Moisture or dirt in the connector
  5. Rarely, a fault in the PCM input circuit

How to diagnose

  1. Scan for codes and freeze frame data, and note any other temperature sensor codes
  2. Compare the scan tool's ambient temperature reading with the actual outside temperature
  3. Inspect the sensor (usually behind the bumper or grille) and its connector for corrosion, moisture or damage
  4. Wiggle the harness and connector while watching live data for dropouts
  5. Measure the sensor's resistance and compare it with the spec for your model
  6. Test the signal and ground wires to the PCM for opens and shorts
  7. Check reference voltage and ground at the sensor connector
  8. Clear the code and confirm it does not return after the repair

Common fixes

  • Clean the connector, secure it and apply dielectric grease
  • Repair or replace the damaged section of wiring
  • Replace the ambient air temperature sensor
  • If an internal input fault is confirmed, repair or replace the PCM

Questions and answers

Can I drive with a P0074 code?

Yes, usually. It does not affect safety or seriously harm the engine. The check engine light will stay on and the climate control may be inaccurate, so get it checked soon.

What most often causes P0074?

Most often it is a poor connection at the sensor connector or a damaged wire, especially where the harness rubs or gets wet. The sensor itself fails less often.

How do I clear P0074?

Fix the cause first by cleaning the connector and checking the wiring and sensor. Then clear the code with a scan tool. If the fault is still there, the code will come back.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.