What it means
A general circuit fault on the intake air heater control - the ECU cannot drive the grid heater at cold-start.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The intake air heater warms incoming air to help a diesel engine start and run cleanly in cold conditions. P0640 sets when the control module detects a fault in the heater control circuit and cannot reliably command the heater during cold-start operation.
Common causes
Most likely first.
- Open or short in intake-air-heater wiring
- Faulty intake-air heater element
- Heater relay or control circuit fault
- Poor connector contact or ground
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
How to diagnose it
- Check freeze-frame data and ambient conditions to see whether the code occurred during a cold start when intake heating would be requested.
- Inspect the intake-air-heater element, its high-current wiring, connectors, and ground for loose connections, corrosion, heat damage, or chafing.
- Check the heater fuse and relay, if fitted, and confirm relay power and control according to the manufacturer's wiring information.
- Measure the heater element and control circuit for an open or short using the manufacturer's specification.
- Command the heater with a scan tool, if supported, and verify the module's control signal and the heater's power supply under load.
Common fixes
- Repair loose, corroded, or heat-damaged intake-heater connections.
- Replace a failed intake-air-heater relay or fuse after checking for an underlying short.
- Repair open or shorted heater-control wiring and restore its ground.
- Replace the intake-air-heater element if it fails its circuit test.
- Repair the module control driver only after confirming the heater, relay, power, and wiring are sound.
Can I keep driving?
The vehicle may be difficult to start or run roughly in cold weather, and repeated unsuccessful starts can drain the battery. If it starts and runs normally, driving is generally possible, but allow for reduced cold-start reliability.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.