P0540 OBD-II Trouble Code: Intake Air Heater "A" Circuit
Diagnostic Trouble Code (DTC): P0540
P0540 code definition
The presence of the P0540 code in the PCM means that an abnormal input voltage was detected from the intake air heater circuit.
What the P0540 code means
The intake air heater is used to warm air so that cylinder combustion happens correctly. During cold operation, the ECM grounds the control coil of the intake air heater relay in order to energize the heater. If the voltage reading from the ECM exceeds the manufacturer’s specifications during this process, the PCM will store the P0540 code.
What causes the P0540 code?
The most frequent causes of the P0540 code include a faulty intake air heater relay, as well as the following causes:
- Shorted, open, or corroded wiring or connectors
- Burnt out heater elements
- Bad intake air heater blower
- Faulty intake air temperature sensor
- Disconnected intake air temperature sensor
- Faulty PCM, in rare cases
What are the symptoms of the P0540 code?
Usually, the only discernible symptoms will be the stored trouble code and the illumination of the Check Engine Light.
How does a mechanic diagnose the P0540 code?
The diagnostic procedure for the P0540 code begins with verifying the code using an OBD-II scanner. Afterwards, all electrical components should be visually inspected to ensure that they are connected and not in need of replacement or repair. After this step, it is important to clear the trouble code from the PCM, and retest the system. If the code returns, the issue likely lies with the intake air heater or the temperature sensor. In addition to an OBD-II scanner, an infrared thermometer, and a digital volt reader will be necessary to properly diagnose this issue.
Common mistakes when diagnosing the P0540 code
Often when a mechanic replaces an air filter, or removes the air cleaner box during other repairs, the intake air temperature sensor may not be reconnected correctly. This can cause the P0540 code to be stored, and should always be checked before replacing any parts.
How serious is the P0540 code?
While little to no symptoms may be observed with the P0540 code, it is still an important issue that must be repaired immediately. If the issue is not addressed, the vehicle may lose the ability to start altogether.
What repairs can fix the P0540 code?
In order to address the P0540 code, a service technician may perform any of the following repairs:
- Replace a faulty intake air heater
- Repair shorted, open, or corroded wiring or connectors
- Replace burnt out heater elements
- Replace a bad intake air heater blower
- Replace a faulty intake air temperature sensor
- Reconnect a disconnected intake air temperature sensor
- Replace a faulty PCM, in rare cases
Need help with a P0540 code?
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