Guide To P0640 OBD Error Code Solutions

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P0640 is a diagnostic trouble code (DTC) for "Intake Air Heater Control Circuit". It indicates that PCM has detected an abnormal input voltage reading from the intake air heater control circuit. The Intake Air Heater warms the air going into the engine on cold startups. If the engine control module (PCM) detects a failure in the Intake Air Heater or its wiring, it will set code P0640. Any voltage variation that is outside the manufacturer’s specifications can lead to a P0640 code.

Error Code P0640 is defined as Intake Air Heater Control Circuit. This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles. This means there’s an abnormal input voltage within the intake air heater control circuit, likely caused by a dirty filter or faulty air heater relay. The intake air heater typically consists of a heater element that becomes functional when battery voltage is applied. Increasing intake air temperature stabilizes fuel atomization and helps to evaporate any moisture that may be present. The PCM uses data input from the intake air temperature (IAT) sensors to determine whether the intake air heater is functioning properly. Vehicles that utilize an intake air heater usually have an IAT sensor before and after the heater element so that the PCM can effectively monitor intake air heater operation. If the PCM detects no difference between intake air temperature after it has passed through the intake air heater element, a code P0640 will be stored and a malfunction indicator lamp (MIL) may be illuminated.

What causes this problem with the Intake Air Heater Control Circuit?

• Disconnected or faulty intake air temperature sensor
• Open or shorted wiring or connectors
• Frayed intake heater blower
• Defective intake air heater relay or fuse
• Burnt intake air heater element
• Faulty PCM

1. Intake Heater Blower - Heater Blower should work efficiently as it is responsible for blowing air throughout. If you discover it faulty, replace or repair it as required.
2. Intake Air Temperature Sensor - The Intake Air Temperature sensor (IAT) monitors the temperature of the air entering the engine. The engine computer (PCM) needs this information to estimate air density so it can balance air air/fuel mixture. As PCM completely depends on this for such information so make sure it should not be malfunctioned.
3. Wiring and Connector - Thoroughly inspect the related wiring and connector as the damaged and corroded one can cause many problems. Repair or replace it as required.
4. PCM - The Powertrain Control Module PCM is an on-board electronic control unit that primarily controls the charging, emission and transmission systems of the vehicle. Though it rarely fails but always inspect that carefully to avoid such situation.

Below mentioned are some common symptoms of the error code P0640:

• Reduced fuel efficiency
• Difficulty while driving when cold
• Rough idle on cold start
• Illuminated check engine light

Due to this error code you may not face any major drivability issues and you can easily solve this code as per your convenience but retaining an error code for long is not a good idea. To fix this code following repairs and replacements may help:

• Inspect the Intake air sensors carefully if found faulty replace them.
• Replace the damaged wiring and connectors.
• Replace the faulty Intake air heater relay or fuse.
• Check out the blower, repair or replace if required.

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Diagnosing this code may require several tools and thorough inspection so it is always recommended that you should get your vehicle diagnosed by an experienced diagnostician. Steps to diagnose this error code are as follows:

• Visually inspect all the related wiring and connectors.
• Test Intake air heater power supply fuses and relays.
• Activate the intake air heater system and locate the intake air heater connector.
• Check for battery voltage and a ground. If no voltage is detected, check system fuses and relays by following manufacturers testing procedures and specifications.
• If no ground is discovered, check the appropriate ground junction on the engine block or chassis.
• Test the sensor voltage (usually 5-volts) and ground at the IAT sensor connector.
• Use the DVOM to trace the circuit back to the appropriate terminal of the PCM connector.
• Use the infrared thermometer to determine the actual temperature of the intake air (before and aft of the intake air heater element).
• Compare the voltage to temp information (found in your vehicle information source) to determine if the IAT sensor/s is functioning normally.

Common Mistakes When Diagnosing the P0640 Code

The most common mistake usually people commit while diagnosing this code is reconnecting the Intake air temperature sensor after replacing the air filter or removing the air cleaner box for repairs. This may cause an intake air heater code to be stored.