Technical Description of OBD-II Trouble Code
Circuit for Controlling Intake Air Heater
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Buick, Chevrolet, Ford, GMC, Mercedes-Benz, Opel, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
If your OBD-II equipped vehicle has stored a code P0640, it means that the powertrain control module (PCM) has detected a malfunction in the intake air heater control circuit.
The intake air heater usually consists of a heater element that becomes operational when battery voltage is applied. Increasing the intake air temperature helps stabilize fuel atomization and aids in evaporating any moisture present. Warmer intake air also improves fuel efficiency.
The intake air heater element is a stationary metal grid that becomes red hot when battery voltage is applied. With the intake air heater element glowing hot, the intake air passes through and around it, resulting in significant heating.
The PCM uses data input from the intake air temperature (IAT) sensors to determine if the intake air heater is functioning correctly. The usage of the intake air heater 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 the operation of the intake air heater.
If the PCM detects no difference in intake air temperature after it has passed through the intake air heater element, it will store a code P0640 and may illuminate a malfunction indicator lamp (MIL). 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 considered severe and addressed accordingly. 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:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0640 troubleshooting steps?
To successfully diagnose a code P0640, you will need several tools.
You will require a diagnostic scanner, a digital volt/ohmmeter (DVOM), and an infrared thermometer with a laser pointer. Additionally, you will need a reliable source of vehicle information.
You can use the vehicle information source to search for technical service bulletins (TSB) that are relevant to your vehicle, engine, symptoms, and exhibited codes. If you find an applicable TSB, it may expedite the diagnosis of the code P0640.
Utilize the vehicle information source to obtain diagnostic flow charts, wiring diagrams, connector face views, connector pin-out charts, and component testing procedures/specifications.
Begin by connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and relevant freeze frame data. Make a note of this information in case it is needed later (after clearing the codes). 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 that caused it may need to worsen before an accurate diagnosis can be made.
If scenario B occurs, proceed with the steps listed below.
Step 1
Conduct a visual inspection of all related wiring and connectors. Check the power supply fuses and relays for the intake air heater. Make any necessary repairs. If no issues are found, proceed to the next step.
Step 2
Refer to the diagnostic flow charts, wiring diagrams, connector face views, connector pin-out charts, and component testing specifications/procedures from your vehicle information source to test the voltage, ground, and signal circuits of the IAT sensor.
Step 3
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, follow the manufacturer’s testing procedures and specifications to check the system fuses and relays. If no ground is found, check the appropriate ground junction on the engine block or chassis. If the circuit is complete (battery voltage and ground), proceed to the next step.
Step 4
Begin by testing the sensor voltage (usually 5 volts) and ground at the IAT sensor connector. If there is no voltage, use the DVOM to trace the circuit back to the appropriate terminal of the PCM connector. If there is no voltage on this pin, suspect that the PCM is defective. If there is voltage at the PCM connector pin, repair the open circuit between the PCM and the IAT sensor connector. If there is no ground, trace the circuit back to the central ground location and make any necessary repairs. If both ground and voltage are present at the IAT sensor connector, proceed to the next step.
Step 5
Use the infrared thermometer to determine the actual temperature of the intake air (before and after the intake air heater element). The scanner data stream will indicate the temperature (or degree of voltage) being input to the PCM. Compare the voltage to temperature information (found in your vehicle information source) to determine if the IAT sensor/s is functioning normally.
If the IAT and all system circuits are functional, suspect a defective PCM or a PCM programming error.
