Error Code P0543 is defined as Intake Air Heater “A” Circuit Open. There’s means an abnormal amount of voltage from the intake air heater circuit has been detected, this is often due to faulty wiring or sensor.


Error Code P0543 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 P0543 is actually 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 Error Code P0543 is set, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicles makes) has detected an open circuit in the intake air heater “A” circuit.

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:

  • Hard starting condition or engine may not start at all
  • Engine stalls
  • Rough idle at a cold temperature
  • Cranking time takes longer than normal

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

Possible Causes

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

  • Loose wiring connection
  • Failed intake air heater relay
  • Open circuit between the air heater relay and PCM
  • Burn out heater elements
  • Corroded, open, or shorted connectors or wirings
  • Defective PCM (rare)

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

Diagnosis for this code usually emphasizes on connectors, wirings, and other electrical components connected to the intake air heater circuit system. Any damaged elements must be replaced, repaired, or reconnected as necessary.

In every repair procedure, it is important to clear the codes and retest the system again to see if the code returns.

How to Fix

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

  • Replacement of faulty intake air heater relay.
  • Repair or replacement of short, faulty, or open wiring, connectors, and other electrical components.
  • Replacement of faulty intake air heater blower.
  • Replacement of burnt out heating element.
  • Replacement of faulty intake air heater.
  • Replacement of open or shorted intake air heater harness.
  • Repair or replacement of a faulty or loose 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.