P0640 – Intake Air Heater Control Circuit (OBD2)
P0640 means "Intake Air Heater Control Circuit". The control unit has detected a fault in the electrical circuit of the intake air heater: the signal or control current is missing or outside the expected window. The code does not say whether the value is too high or too low, so the wiring and the component itself both have to be checked.
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P0640 quick summary
| Fault code | P0640 |
|---|---|
| Meaning | Intake Air Heater Control Circuit |
| System | Powertrain (Engine & Transmission) |
| Vehicles | Generic OBD2 |
| Severity | Low |
| Can I drive? | Yes. Expect harder starts and white smoke in cold weather. A relay stuck on can drain the battery or overheat the heater, so check it soon. |
| Repair cost | €30 – €500 |
How the intake air heater works
Some diesel engines heat the intake air electrically or with a flame heater to improve cold starting and reduce white smoke; these codes cover the heater and its control circuit.
Instead of or in addition to glow plugs, some diesel engines – mainly larger engines in vans, trucks and pick-ups – have a heating grid or flame starter in the intake manifold. It is switched by a relay controlled by the engine control unit and draws a very high current.
Codes P0540–P0543 and P0640 report faults in the heater circuit or its control: open, low, high or a control circuit fault. A failed heater makes cold starts difficult and causes white smoke.
Typical causes are a burnt-out heating element, a stuck or failed relay, corroded high-current terminals and damaged cables.
On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 17024 (P0640). Both numbers mean the same fault.
Symptoms of P0640
- Hard starting in cold weather
- White smoke after a cold start
- Check Engine or wait-to-start light
- Battery drained (relay stuck on)
- Usually normal running when warm
Most common causes of P0640 (most likely first)
Mechanic's Pro Tip
If the battery goes flat overnight on an engine with an intake heater, check whether the heater relay has welded its contacts and keeps the heater on.
1.Damaged wire or loose, corroded connector at the intake air heater
Most likelyGreen or white corrosion, pushed-back pins and chafed insulation near hot or moving parts are the most common findings.
2.Faulty intake air heater
An internal break or short in the component itself.
3.Blown fuse or missing supply voltage
If several codes appeared at the same time, check the shared fuse, relay or ground point first.
4.Burnt-out heating element
5.Corroded high-current terminals or cables
6.Control circuit fault
Step-by-step diagnostic guide
- 1
Read codes
Read all codes and note whether they concern the heater or the control circuit.
- 2
Check the circuit with a multimeter
With the ignition off, unplug the intake air heater and the control unit connector (or back-probe), then check each wire between them for continuity and for shorts to ground and to battery voltage. Compare the component's resistance or supply voltage with the value in the repair manual.
Multimeter: Wire continuity: below about 1 Ω. Wire to ground with both connectors unplugged: no continuity. Supply/reference with ignition on: usually 5 V for sensors, battery voltage for actuators.
- 3
Check the relay
With the ignition on in cold conditions, check whether the relay clicks and supplies voltage to the heater.
- 4
Measure the heater
Measure the heater resistance or current draw.
Multimeter: Heating grids have a very low resistance (well below 1 Ω) and draw a high current – compare with the specification.
- 5
Check terminals and cables
Inspect the high-current terminals for corrosion and burnt marks.
- 6
Replace and verify
Replace the faulty part and confirm normal operation on the next cold start.
Frequently asked questions
Can I keep driving with P0640?
Yes. Expect harder starts and white smoke in cold weather. A relay stuck on can drain the battery or overheat the heater, so check it soon.
How much does it cost to fix P0640?
Typical repair costs are 30 € – 500 €, depending on the cause and the vehicle. The most common fixes are: damaged wire or loose, corroded connector at the intake air heater; faulty intake air heater; blown fuse or missing supply voltage. Always confirm the cause with the tests above before buying parts.
Is an intake air heater the same as glow plugs?
No. Glow plugs heat each combustion chamber, while the intake air heater warms the air in the intake manifold. Some engines have both.
Can I drive with an intake heater code?
Yes, but cold starts will be harder and smokier.
What is the difference between P0640 and similar codes?
P0640 belongs to a group of codes for the same component that differ in the type or location of the fault: P0540 – Intake Air Heater A Circuit; P0541 – Intake Air Heater A Circuit Low; P0542 – Intake Air Heater A Circuit High; P0543 – Intake Air Heater A Circuit Open. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.