P0640 Intake Air Heater Control Circuit
OBD-II Trouble Code Technical Description
Intake Air Heater Control Circuit
What does that mean?
This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Buick, Chevrolet, Ford, GMC, Mercedes-Benz, Opel, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
If a code P0640 has been stored in your OBD-II equipped vehicle, it means that the powertrain control module (PCM) has detected a malfunction in the intake air heater control circuit.
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. Warmer intake air also promotes greater fuel efficiency.
The intake air heater element is a stationary metal grid that actually becomes red hot when battery voltage is applied. With the intake air heater element glowing hot, intake air passes through and around it and is heated significantly.
The PCM uses data input from the intake air temperature (IAT) sensors to determine whether the intake air heater is functioning properly. Intake air heater usage is limited. 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. In most cases, MIL illumination will require more than one ignition cycle with a failure.
A typical air intake heater:
What is the severity of this DTC?
Intake air temperature codes should be classified as severe and addressed as such. A code P0640 may be accompanied by various drivability symptoms, especially when the engine is cold.
What are some of the symptoms of the code?
Symptoms of a P0640 trouble code may include:
Diminished fuel efficiency Rough idle on cold start Drivability issues when cold Other IAT codesWhat are some of the common causes of the code?
Causes for this code may include:
Defective or disconnected intake air temperature sensor Faulty intake air heater relay or fuse Shorted or open wiring or connectors Burnt out intake air heater element Bad PCM or programming errorWhat are some P0640 troubleshooting steps?
You will need several tools to successfully diagnose a code P0640.
A diagnostic scanner and a digital volt/ohmmeter (DVOM), as well as an infrared thermometer with a laser pointer, will be required. A reliable source of vehicle information will also be necessary.
You can use the source of vehicle information to search for technical service bulletins (TSB) that parallel the vehicle, engine, symptoms, and codes exhibited in your situation. If you find an applicable TSB, it may help you to diagnose the code P0640 more rapidly.
Use the vehicle information source to obtain diagnostic flow charts, wiring diagrams, connector face views, connector pin-out charts, component testing procedures/specifications.
Begin by connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and pertinent freeze frame data. Write this information down in case you need it later (after the codes are cleared). Next, clear the codes and test drive the vehicle until one of two scenarios occurs:
A. The code fails to reset and the PCM enters readiness mode
B. The code is reset
If scenario A occurs, you are dealing with an intermittent code and the conditions which caused it may have to worsen before an
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