| Intake air heater A -circuit malfunction
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|Wiring, relay, intake air heater
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Table of Contents
- What Does Code P0540 Mean?
- What are the common causes of code P0540 ?
- What are the symptoms of code P0540 ?
- How do you troubleshoot code P0540 ?
- Codes Related to P0540
- Get Help with P0540
What Does Code P0540 Mean?OBD II fault code P0540 is defined as “Intake Air Heater "A" Circuit Malfunction”, and is set when the PCM (Powertrain Control Module) detects an abnormal input voltage from, or in the intake air heater circuit. Variations in the input circuit voltage that fall outside of a predetermined range will set a trouble code, and may trigger a warning light. Note that not all applications will set a code and trigger a warning light on the first failure; some applications require multiple fault cycles to occur before setting a code, and/or triggering a warning light. Typical intake air heating systems consist of a heating element, a blower to move the heated air into the engine, and various electrical components that include wiring, connectors, a temperature sensor, and a relay. The function of the intake air heater is to warm up the intake air to improve combustion at low temperatures. While most applications use a coiled element that is placed directly in the intake air’s flow path, others use a variety of designs that increase the elements’ surface area, thereby making the element more efficient. Regardless of the actual design of the element though, the purpose of the element is the same in all cases, which is to heat the intake air to improve combustion. Note however that the intake air heating system only comes into operation when the ambient temperature falls below a level determined by the manufacturer. There are several advantages to heating the intake air. Reducing the volume of air entering the engine by heating it means that less fuel is required to maintain the optimal air/fuel ratio, since a hot air/fuel mixture combusts more completely than does a cold mixture. This results in fewer emissions, and improved fuel economy. By way of contrast, applications that do not heat the intake air must add additional fuel to the incoming cold air to compensate for the greater density of cold air, which results in increased emissions and increased fuel consumption. The image below shows the typical construction and location of an intake-air heating element. Note however that actual designs vary between applications and manufacturers. Note: “Circuit Malfunction” indicates that there is a malfunction in the control circuit, as opposed to a fault in a sensor or other component. With “Circuit Malfunction” codes, replacement of sensors and components in the affected circuit will almost never resolve the problem, since as the code suggests, the trouble is in the circuit. This distinction between “circuit” and “sensor/component” is a great help to anyone trying to diagnose a circuit malfunction code, since it narrows the list of possible causes down considerably.
What are the common causes of code P0540 ?The most common cause of code P0540 is failure of the intake air heater element relay, but other possible causes could include the following-
- Defective heater element
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors.
- Open circuits
- Defective blower motors
- Defective intake air temperature sensor
- Failed, or failing PCM. Note that this is a rare event and the fault must be sought elsewhere before any controller is replaced.
What are the symptoms of code P0540 ?In many cases, there may be no symptoms present other than a stored trouble code and perhaps an illuminated warning light. Serious symptoms that affect driveability are relatively rare, but these might include the following in sub-zero temperatures-
- Longer than usual cranking times.
- Rough idling in very low temperatures. Note that this symptom will usually diminish as the engine warms up.
- In rare cases, the engine might stall during idling in very low temperatures.
- In some cases, a slight increase in fuel consumption might occur.
How do you troubleshoot code P0540 ?WARNING: Avoid touching the heater element directly during the diagnostic/repair/replacement process. The element can heat up at any moment, and it can do so faster than you can release it. To prevent the distinct possibility of sustaining serious burns, always use a laser-based thermometer to check the operation of the element. NOTE: Before starting a diagnostic procedure if the intake air heating control circuit, check to see if the connector is secure. Many people (including mechanics) often fail to reconnect the connector properly after performing routine servicing. Step 1 Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on. Step 2 Consult the repair manual for the application to determine the location, function, color-coding, and routing of all associated wiring, and perform a thorough visual inspection of all wiring and connectors. Look for damaged, burnt, shorted, disconnected, and/or corroded wiring and connectors. Make repairs as required, clear all codes, and retest the system to see if the code returns. Step 3 If the code persists, but no visible damage to wiring and connectors is found, perform reference voltage, ground, resistance, and continuity checks on all wiring, fuses, and relays, but be sure to disconnect the circuit from the PCM to prevent damage to the controller. Compare all obtained readings to those stated in the manual, and make repairs as required to ensure that all readings fall within the manufacturer’s specifications. NOTE1: Pay particular attention to the resistance of the element itself, as well as the resistance of the input voltage wire. High resistance in this wire can cause a significant current loss, which has a serious affect on the operation of the heater element. Also, be sure to double check all ground connections in the circuit, since loss of ground is one of the major causes of code P0540. Step 4 If all electrical values for the heating element check out OK perform reference/input voltage, ground, resistance, and continuity checks on all wiring associated with the blower motor. Note that the blower motor forms part of the circuit, and its resistance / continuity must therefore be checked as well. Compare obtained readings with those stated in the manual, and replace the blower motor if its internal resistance does not fall within specifications. Also, check the internal resistance of the intake air temperature sensor, and replace it if it does not agree with the manufacturer’s specifications. NOTE: On applications that use MAF (Mass Airflow) sensors, the intake air temperature sensor is incorporated into the sensor body. Consult the manual to determine the correct pins in the connector to avoid testing the wrong sensor. Step 5 Clear all codes after repairs/replacements are complete. If the scanner has control functions, activate the heater element several times to check for intermittent faults. However, do NOT touch the heater element to see if it heats up- use a laser based thermometer to measure its temperature to avoid possible personal injury. The blower motor should also start as soon as current is fed to the element. Use the scanner to measure the motor’s current draw, and compare this reading to the value stated in the manual. Replace the motor if its current draw fluctuates during operation. NOTE: Be aware that the intake air heating circuit might not work automatically if the ambient and/or engine temperature is above a limit set by the manufacturer. Nonetheless, the circuit should activate if it is commanded “ON” with a scanner, or if current is applied directly, but be sure to consult the manual on the correct procedures to apply direct current to any circuit. Step 6 At this point, the circuit and all components should function properly but if the code returns after a few drive cycles, it is likely that there is an intermittent fault present. Be aware that intermittent faults can be extremely challenging and time consuming to find and repair, and in some cases, it might be necessary to allow the fault to worsen before an accurate diagnosis and definitive repair can be made.
Codes Related to P0540
- P0543 – Relates to “Intake Air Heater "A" Circuit Open”
- P0542 – Relates to “Intake Air Heater "A" Circuit High”
- P0541 – Relates to “Intake Air Heater "A" Circuit Low”
- P0540 – Relates to “Intake Air Heater "A" Circuit”
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