Intake Air Heater "A" Circuit


The PCM has detected an abnormal input voltage reading from the intake air heater 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 successfully diagnosing this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis
  • An infrared thermometer with a laser pointer will also be helpful