The ECU has failed its own memory checksum — sometimes fixable, sometimes ECU replacement.
P0601 — also written PO6O1, P 0601, 0601 — is the OBD-II code for internal control module memory check sum error. Same code, same fix: this page covers every spelling of it.
This is the ECU telling you it’s got a 'digital migraine'—the internal maths doesn't add up anymore. We see this a lot on older Vauxhalls and VWs where water has got into the pins or a dodgy remap has corrupted the files.
P0601 is a electrical fault code, typically costing £80–£1500 to put right in a UK garage.
What P0601 actually feels like to drive
- The car won't even turn over, just a clicking from the dash.
- Engine starts for two seconds then dies (immobiliser kicking in).
- Stuck in 'Limp Home Mode' with no power going up hills.
- The cooling fan runs at full speed as soon as the ignition is turned on.
- Random dash lights appearing like a Christmas tree, especially the padlock or wrench symbol.
What causes P0601?
- Corrupted ECU software after failed remap or coding
- Water ingress in ECU
- Failed ECU
UK vehicles that throw P0601 most often
- Vauxhall Corsa D 1.2/1.4 (A12XER) 2006-2014 (Water ingress)
- Volkswagen Golf Mk5 1.9 TDI (BKC/BXE) 2004-2009 (Remap failures)
- Ford Focus Mk2 1.6 Ti-VCT 2005-2011 (Instrument cluster/ECU comms)
- Vauxhall Astra J 1.7 CDTi 2009-2015 (Delphi ECU issues)
- BMW 3 Series (E90) 320d 2005-2011 (EDC16/17 Checksum errors)
- Audi A3 2.0 TDI (BKD) 2003-2012 (ECU internal hardware failure)
How P0601 is fixed
- Reflash ECU with correct file
- Dry and reseal ECU
- Replace or repair ECU
The P0601 misdiagnosis that wastes money
I see folks panic and start swapping out sensors like there's no tomorrow, thinking a dodgy MAF or crank sensor is causing the limp mode. But this isn't a sensor issue—it's the brain itself having a stroke. The biggest blunder I see is people buying a second-hand ECU off eBay for £50, plugging it in, and then wondering why the car won't even crank. You can't just 'plug and play' these; the immobiliser data is baked in. Most of the time, the fault was actually caused by a 'Blackgate' or 'parking lot' remapper who didn't know how to calculate a checksum properly during a cheap stage 1 tune.
What a UK garage should charge for P0601
If it’s just a software flash, expect to pay £80 to £120 at a good indie. If the ECU is water-damaged, a professional repair by a specialist UK lab usually sits around £250 to £400 plus labour. If you go to a main dealer for a brand new Bosch or Continental unit, you're looking at £1,000 to £1,500 once you factor in the VAT and two hours of 'dealer-only' programming time. Always try a software reset or a specialist repair first—it's the difference between a cheap fix and a car being written off.
P0601 repair cost in the UK
Most P0601 repairs land between £80–£1500 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 P0601
If you've just had the car remapped and this pops up, get straight back to the tuner and demand they restore the original map—that usually clears the checksum error instantly. If it’s a standard car, ask your garage if they have 'Pass-Thru' capability to do a software update from the manufacturer server. If the ECU is physically toast, don't let a main dealer talk you into a £1,500 new unit. Look for a specialist firm like ECU Testing in Derbyshire or ACtronics. They can often rebuild your original unit for about £300, meaning you don't have to pay for expensive recoding or key matching.
Can you drive with P0601?
Car may not run properly.
Urgency: high.