P0645: A/C clutch relay control: circuit fault
The ECU detects a fault in the relay circuit that engages the air conditioning compressor. Usually the relay, a fuse or the wiring.
| Code | P0645 |
|---|---|
| System | Engine and transmission |
| Group | P06xx, Control unit and auxiliary outputs |
| Type | Generic: it means the same on every make |
| Can you keep driving? | Yes, no rush |
What P0645 means
For the air conditioning to cool, the ECU switches a relay that engages the compressor clutch. This code means that relay’s control circuit is not responding properly. The usual result is air conditioning that does not cool.
Most common causes
- Faulty or poorly seated compressor relay
- Blown air conditioning fuse
- Relay or compressor plug loose or corroded
- Control wire broken or chafed
- Faulty compressor clutch coil
Symptoms
- Engine warning light on
- Air conditioning not cooling
- Compressor not engaging, or engaging when it should not
Can you drive with P0645?
Yes, no rush It does not affect the engine or safety. You can drive normally, just without air conditioning.
Open the bonnetthe in-depth explanation
How to check it
With the engine running and the air conditioning on, check whether the front plate of the compressor spins with the pulley. If not, check the compressor fuse and relay first.
How to read and clear P0645 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0645 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0641 Sensor reference voltage A: circuit open or faulty
- P0642 Sensor reference voltage A: circuit low
- P0643 Sensor reference voltage A: circuit high
- P0644 The driver display series communication has an electrical fault
- P0646 The air conditioning clutch relay control gives a lower signal than normal
- P0647 The air conditioning clutch relay control gives a higher signal than normal
- P0648 The immobiliser light control has an electrical fault
- P0649 The speed control light control has an electrical fault
- P0600 Serial communication link fault
- P0601 Internal control module memory checksum error
- P0602 Control module programming error
- P0603 Internal control module keep alive memory (KAM) error
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Air conditioning.
What does code P0645 mean?
For the air conditioning to cool, the ECU switches a relay that engages the compressor clutch. This code means that relay’s control circuit is not responding properly. The usual result is air conditioning that does not cool.
Can you drive with P0645?
It does not affect the engine or safety. You can drive normally, just without air conditioning.
How do you clear P0645?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0645 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
