What does it mean?
This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles (1996-newer). This 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 the year, make, model, and powertrain configuration.
If a P0640 code has been stored in your OBD-II equipped vehicle, it means the Powertrain Control Module (PCM) has detected a malfunction in the intake air heater control circuit.
The intake air heater typically consists of a heating element that becomes operational when battery voltage is applied. Increasing the intake air temperature stabilizes fuel atomization and helps evaporate any moisture that may be present. Warmer intake air also promotes greater fuel efficiency.
The intake air heater element is a fixed metal grid that actually glows red when battery voltage is applied. With the intake air heater element being 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 if the intake air heater is operating correctly. The use of the intake air heater is limited. Vehicles that use an intake air heater typically have an IAT sensor before and after the heating element so the PCM can effectively monitor the intake air heater’s operation.
If the PCM detects no difference in the intake air temperature after it has passed through the intake air heater element, a P0640 code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated. In most cases, MIL illumination will require more than one ignition cycle in case of failure.
A typical intake air heater:
P0640 Intake Air Heater
How severe is this DTC?
Intake air temperature codes should be classified as severe and treated as such. A P0640 code may be accompanied by various driveability symptoms, especially when the engine is cold.
What are some of the symptoms of the code?
Symptoms of a P0640 trouble code may include:
Reduced fuel economy
Rough idle on cold start
Cold driveability issues
Other IAT codes
What are some of the common causes of the code?
Causes
of this code may include:
Faulty or disconnected Intake Air Temperature sensor
Faulty intake air heater relay or fuse
Shorted or open wiring or connectors
Burned out intake air heater element
Faulty PCM or PCM programming error
What are the P0640 troubleshooting steps?
You will need several tools to successfully diagnose a P0640 code.
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 vehicle information source to look for Technical Service Bulletins (TSBs) that match the vehicle, engine, symptoms, and codes displayed in your situation. If you find an applicable TSB, it may help you diagnose the P0640 code more quickly.
Use the vehicle information source to obtain diagnostic flowcharts, wiring diagrams, connector face views, connector pinout diagrams, component test procedures/specifications.
Start by connecting the scanner to the vehicle’s diagnostic port and retrieve all stored codes and relevant freeze frame data. Note this information in case you need it later (once the codes are cleared). Then, clear the codes and test drive the vehicle until one of two scenarios occurs:
A. The code does not 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 to the steps listed below.
Step 1
Perform a visual inspection of all associated wiring and connectors. Check the intake air heater power fuses and relays. Perform necessary repairs. If no issues are detected, proceed to the next step.
Step 2
Use the diagnostic flowcharts, wiring diagrams, connector face views, connector pinout diagrams, and component test specifications/procedures from your vehicle information source to test the IAT sensor voltage, ground, and signal circuits.
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, check the system fuses and relays following the manufacturer’s test procedures and specifications. 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 (typically 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 on the PCM connector. If there is no voltage at that pin, suspect a faulty PCM. 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 to the central ground location and perform necessary repairs. If ground and voltage are detected at the IAT sensor connector, proceed to the next step.
Step 5
Use the infrared thermometer to determine the actual intake air temperature (front and rear of the intake air heater element). The scanner data stream will reveal what temperature (or degree of voltage) is being input to the PCM. Compare the voltage to temperature information (found in your vehicle information source) to determine if the IAT sensor(s) are operating normally.
If the IAT and all system circuits are functional, suspect a faulty PCM or a PCM programming error.
If the scanner reveals an irrational IAT (such as -38 degrees when the ambient temperature is much warmer), suspect an open circuit situation has occurred
Disconnected IAT sensors are common after air filter element inspection/maintenance