Ambient Air Temperature Sensor Circuit


This code indicates that the PCM has received an abnormal signal from the ambient air temperature sensor.

Code Set Parameters

Any ambient air temperature reading that exceeds the perceived temperature of the intake air, will cause a code to be stored in the PCM and a service engine soon lamp to be illuminated.


Typically, a service engine soon lamp will be the only visible symptom of this condition. In some instances, the electronic climate control system will also be disabled.

Common Causes

Causes of this code usually include a faulty ambient temperature sensor, disconnected electrical connectors, shorted, open, or corroded electrical circuitry or electrical connectors. Objects or road debris covering the ambient air temperature sensor can also affect input voltage readings.

Common Misdiagnosis

Ambient air temp sensors are frequently replaced in error when defective wiring and/or connectors are the culprits.


  • If your vehicle is equipped with an ambient temperature sensor (usually a two or three-wire variable resistance sensor), it is designed to provide the PCM and the body control module (for convenience display items) with data
  • The sensor has a voltage wire (typically it is a 5-volt reference signal) and a ground wire
  • The PCM uses the reference voltage wire to monitor ambient air temperature
  • As ambient air temperature increases, sensor resistance decreases and reference voltage increases
  • When ambient air is cool, sensor resistance is high, driving reference voltage to the PCM down
  • The PCM receives input reference voltage readings as variations in ambient air temperature and reacts accordingly
  • If ambient air temperature exceeds intake air temperature, a code is stored and a service engine soon lamp is illuminated. You will need a scanner or a code reader and a digital volt ohmmeter to successfully diagnose this code. Begin your diagnosis by visually inspecting all wiring and connectors
  • Look for shorted or burned wiring and replace circuitry and connectors as required
  • If the system wiring, connectors, and components appear to be in normal working order, connect the scanner to the diagnostic connector and record all stored trouble codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • After the codes are cleared, operate the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made. Proceed by unplugging the electrical connector from the ambient air temperature sensor and testing for reference voltage
  • This is usually 5-volts but consult your manufacturer’s service manual to be sure
  • If there is a 5-volt signal present with the ignition turned to the run position, and then check the sensor ground wire
  • If both the reference signal and the ground signal are present, test the sensor resistance using the manufacturer’s temperature to resistance chart
  • Compare your findings to the manufacturer’s specifications and replace the sensor if it fails to comply. If the sensor and voltage at the sensor are within acceptable specifications, disconnect the PCM electrical connector and test circuit continuity and resistance between the sensor and the PCM
  • Repair or replace system circuitry and components as required and retest the system. Should all system circuitry and sensors check out, suspect a faulty PCM but keep in mind that PCM failure is rare and PCM replacement will require reprogramming.