Intake Air Heater Control Circuit


The PCM has detected an abnormal input voltage reading from the intake air heater control circuit.

Code Set Parameters

Voltage variations that exceed the manufacturer’s stipulated level will result in a stored code and an illuminated service engine soon lamp. Some models require multiple drive cycles (usually 3) with a failure to illuminate the service engine soon lamp.


Symptoms accompanying this code are likely to be only the stored code and a service engine soon lamp.

Common Causes

Technicians report the most common cause of this code being a faulty intake air heater relay. Other causes may include shorted or open wiring or connectors, a burnt out heater element, a bad intake air heater blower, a faulty or disconnected intake air temperature sensor, or a faulty PCM. PCM failure is rare.

Common Misdiagnosis

Intake air temperature sensors are frequently not reconnected after replacing the air filter or removing the air cleaner box for repairs. This may cause an intake air heater code to be stored.


  • The intake air heater system is designed to warm air coming into the engine intake system so that it can be used more efficiently
  • Cooler, denser air provides more engine performance but warmer air yields increases in fuel efficiency
  • The typical intake air heater system consists of a heating element similar to the one used in a clothes dryer, a blower to move the warmer air into the engine intake, and an intake air heater relay
  • The entire system sounds a lot like a vacuum cleaner when it is activated (usually only on cold engine startup). Several tools will be instrumental in attempting to successfully diagnose this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in trying to perform a successful diagnosis
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive 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 even be attempted
  • Crank the cold engine
  • Observe scanner data to see if the intake air heater is commanded “ON” by the PCM
  • If it is commanded on, do you hear the blower operating? If the blower is operating, find and expose the heater element to see if it is getting warm
  • Use caution when dealing with the heater element as bodily injury or damage to vehicle components may occur. Test the intake air heater relay by checking voltage and ground signal readings at the electrical connector
  • Compare your actual findings with manufacturer’s specifications
  • If voltage readings fail to comply, disconnect the PCM connector and perform a circuit continuity and resistance test using the digital volt/ohmmeter
  • If the blower fails to operate with the heater, check for voltage and ground signals and compare your findings with manufacturer’s specs
  • Repair open or shorted circuits as required
  • If the heater element is not warming, check for a voltage and ground signal when the system is activated
  • If voltage and ground signals fail to coincide with manufacturer’s specifications, repair open or shorted wiring or connectors as required
  • Some models will allow you to use the scanner to turn the intake air heater on and off
  • Using this function is particularly handy after the engine has warmed.