P0640 Intake Air Heater Control Circuit

Description and meaning of DTC p0640

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.

p0640 diagnostic trouble code symptoms

Symptoms of a P0640 trouble code may include:Diminished fuel efficiencyRough idle on cold startDrivability issues when coldOther IAT codes

DTC p0640 - possible causes

Causes for this code may include:Defective or disconnected intake air temperature sensorFaulty intake air heater relay or fuseShorted or open wiring or connectorsBurnt out intake air heater elementBad PCM or programming error

How to fix OBD-II diagnostic trouble code p0640

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 modeB. The code is resetIf scenario A occurs, you are dealing with an intermittent code and the conditions which caused it may have to worsen before an accurate diagnosis can be made. If scenario B occurs, continue with the steps listed below. Step 1Perform a visual inspection of all related wiring and connectors. Check intake air heater power supply fuses and relays. Make repairs as required. If no problems are found, proceed to the next step. Step 2Use diagnostic flow charts, wiring diagrams, connector face views, connector pin-out charts, and component testing specifications/procedures from your vehicle information source to test IAT sensor voltage, ground, and signal circuits. Step 3Activate 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. If the circuit is complete (battery voltage and ground), proceed to the next step. Step 4Begin with a test of 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 repairs as needed. If ground and voltage are discovered at the IAT sensor connector, proceed to the next step. Step 5Use the infrared thermometer to determine the actual temperature of the intake air (before and aft 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 temp 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. If the scanner reveals an irrational IAT (such as -38-degrees when ambient temperature is much warmer) suspect that an open circuit situation has occurredDisconnected IAT sensors are common after the air filter element is checked/serviced

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