Error Code P0540 is defined as Intake Air Heater “A” Circuit. This means an abnormal voltage input has been detected from the intake air heater circuit.


Error Code P0540 is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present, and with air intake heater, such as Ford (Powerstroke), Chevrolet GMC (Duramax), Dodge, Honda, Nissan, etc. Though generic, specification on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

Error Code P0540 is one of a number of possible codes associated with a malfunction in the intake air heater circuit, which is an essential component of diesel engines that assists the starting process.

The job of the Intake Air Heater “A” is to operate the component that provides warm air that facilitates diesel engine starting and idling at various temperatures. This usually includes a heater element, temperature sensor, relays, and blower(s). There are also routed air ducts to route the warm air to the intake and electrical connections and wiring control for the operation of these components.

When the code P0540 is set, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicles makes) has received an abnormal signal coming the from intake heater “A” circuit, suggesting an improper airflow, faulty component, or out-of-range condition. This malfunction can be caused by a physical, electrical, or mechanical problem.

Other related codes include:

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common and noticeable symptoms include:

  • Engine not starting
  • Engine stalls
  • Rough idle at cold temperature
  • Cranking time takes longer than normal

There are some cases where the vehicle may not show discernible symptoms for this code.

Possible Causes

Defective intake air heater relay is the most common cause for this code. Other possible causes include:

How to Check

As with most error codes, it is important to check the TSB (Technical Service Bulletin) of your specific vehicle including its year, model, and powertrain, to save time and money in the right diagnosis and repairs.

Intake Air Heating Circuit may not automatically work if the ambient air temperature or engine temperature is more than the limit set by the manufacturer. The circuit should activate automatically if commanded “ON” by the scanner, or if power is applied manually.

Basic Diagnosis

  • Check whether the heater element is turning “ON”

Note: Make sure you don’t touch the element or heat shield

  • Check if the blower motor is turning “ON”
  • Check the circuit connections and wiring for obvious defects
  • Check electrical connections for signs of damages, such as corrosion and security issues
  • Check the condition of the air ducts for signs of damages and defects

Advanced Diagnosis

This is usually vehicle specific and may require a specific set of tools and advanced equipment to be performed accurately, such as a digital multimeter, specific technical service reference for the vehicle, etc. Also, the vehicle’s voltage requirement can differ depending on the year, model, and engine.

Specific Checks: Note:

For vehicles with MAF (Mass Airflow) sensors, the intake temperature sensor is incorporated into the sensor body. In this situation, you need to consult the technical data to determine the right pins associated with the sensor.

Specific checks are also needed for troubleshooting specific vehicles, and this includes referring to the technical service manual, especially on checking the power and ground to each component within the intake heater circuit in the proper sequence.

If the voltage is right in a specific component that is not functioning, that usually means the components is defective and requires replacement. If there is no power available to run the circuit, then it must be checked for continuity to identify the faulty components and wirings.

How to Fix

Depending on the diagnosis, common repairs for this code include:

  • Replacement of faulty intake air heater
  • Repair of shorted, open, or corroded wiring or connectors
  • Replacement of burnt out heater elements
  • Replacement of bad intake air heater blower
  • Replacement of faulty intake air temperature sensor
  • Reconnection of disconnected intake air temperature sensor
  • PCM replacement (in rare cases)

The severity of this condition varies from moderate to serious, which is largely based on specific malfunction.