Air-con compressor clutch relay fault.
P0645 — also written PO645, P 0645, 0645 — is the OBD-II code for a/c clutch relay circuit. Same code, same fix: this page covers every spelling of it.
This code means the car's brain can't talk to the air-con compressor clutch. It's a common headache on Ford and Vauxhall models where a cheap relay or a bit of corroded wiring ruins your summer.
P0645 is a electrical fault code, typically costing £40–£400 to put right in a UK garage.
What P0645 actually feels like to drive
- Air conditioning blowing warm air despite being turned to 'Lo'
- The 'click' you usually hear when turning the A/C on is missing
- Engine RPM doesn't dip slightly when the A/C button is pressed
- A/C light on the dash stays on, but there's no cooling effect
- Occasional burning smell from the engine bay if the relay is sticking
What causes P0645?
- Failed relay
- Failed compressor clutch
- Wiring fault
UK vehicles that throw P0645 most often
- Ford Fiesta Mk7 1.25/1.4 Duratec (2008-2017)
- Vauxhall Astra J 1.4/1.6 Turbo (2009-2015) Peugeot 208 1.2 PureTech (2012-2019)
- Volkswagen Golf Mk6 1.6/2.0 TDI (2008-2013)
- Honda Civic 1.8 i-VTEC (2006-2012) — notorious for relay failure
- Ford Transit Custom 2.2 TDCi (2012-2016)
How P0645 is fixed
- Replace relay
- Test compressor
- Repair wiring
The P0645 misdiagnosis that wastes money
I see lads wasting time and money throwing new A/C compressors at this code before they’ve even opened the fuse box. In my experience, especially on the Mk7 Fiestas and Peugeot 208s, it’s rarely the expensive compressor unit itself. We often find the relay has simply burnt out or, more annoyingly, the wiring loom has rubbed through near the radiator support, causing a short that fries the relay. Don’t buy a £300 compressor until you’ve verified the £15 relay and the wiring path.
What a UK garage should charge for P0645
A basic diagnostic plug-in will cost you £50 to £80 at an indie shop. If it’s just the relay, you’re looking at £15 for a Bosch or Denso part plus 15 minutes of labour—call it £40 total. However, if the compressor clutch coil has burnt out, a quality replacement unit (like Hella or Mahle) will run you £250 plus £100 labour and a £50 regas. Main dealers will easily double these prices, often quoting £700+ for a full compressor swap when a £10 relay would have done.
P0645 repair cost in the UK
Most P0645 repairs land between £40–£400 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0645
If you’re taking this to a garage, don't just ask for an 'A/C regas'—that won't fix P0645. Tell them you have a circuit code and insist they perform a 'relay bypass test' to see if the clutch actually clicks. If the garage tries to sell you a full compressor without checking the relay in front of you, walk away. A quick way to check yourself is to swap the A/C relay with an identical one (like the horn relay) in the fuse box and see if the cold air returns. If it does, you’ve saved yourself a few hundred quid.
Can you drive with P0645?
Yes but no A/C.
Urgency: low.