Keep-alive memory error — usually from battery disconnection.
P0603 — also written PO6O3, P 0603, 0603 — is the OBD-II code for internal control module kam error. Same code, same fix: this page covers every spelling of it.
P0603 means the ECU has lost its 'scratchpad' memory—basically, it's forgotten everything it learned about your driving style and sensor offsets because the power was cut. It's very common on Fords and Nissans after a cold snap kills a weak battery.
P0603 is a electrical fault code, typically costing £20–£900 to put right in a UK garage.
What P0603 actually feels like to drive
- The car 'hunts' for a steady idle when you stop at the lights.
- Fuel economy has tanked suddenly because the long-term trim was wiped.
- Radio asking for a code or clock reset to 00:00.
- Engine feels 'flat' or hesitant for the first 20 miles after a start.
- Stalling when dipping the clutch coming up to a roundabout.
What causes P0603?
- Recent battery disconnect
- Failing internal ECU battery
- Water damage
UK vehicles that throw P0603 most often
- Ford Focus Mk2/Mk3 1.6 TDCi (2008-2015)
- Nissan Qashqai J10 1.5 dCi (2007-2013)
- Vauxhall Corsa D 1.2/1.4 (2006-2014) - especially with water in the tray.
- Land Rover Discovery 3/4 TDV6 (Battery sag during start)吹
- Mazda 6 2.2 SkyActiv-D (2012-2017)
- Volkswagen Golf Mk6 2.0 TDI (CRBC/CFGB engines)
How P0603 is fixed
- Clear code, drive for adaption relearn
- Replace ECU if persistent
The P0603 misdiagnosis that wastes money
I see lads jumping the gun and condemning the engine ECU straight away, which is a pricey mistake. They see 'Internal Control Module' and panic. In reality, nine times out of ten, it’s just someone who swapped the battery and didn't use a memory saver, or a lazy apprentice who left the terminal loose. I’ve also seen it triggered by cheap aftermarket HID headlight kits or dodgy 'tuning boxes' that mess with the voltage rail during cranking. Don't buy a new brain for the car until you've checked the basics.
What a UK garage should charge for P0603
A simple code clear and 'drive-cycle' relearn will usually cost you £40-£60 for a diagnostic plug-in. If the battery is the culprit, a decent Bosch or Yuasa unit fitted will be £120-£180. Now, if the ECU internal memory is actually knackered, a new one from a main dealer can easily top £900 plus coding. I usually send them off for a rebuild for about £250-£350, which comes with a lifetime warranty and keeps the original VIN coding.
P0603 repair cost in the UK
Most P0603 repairs land between £20–£900 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 P0603
If a garage tells you the ECU is 'fried' because of P0603, ask them if they’ve checked the parasitic draw and the grounding points on the chassis. Insist on a 'hard reset' first—disconnect the battery, join the leads together (away from the battery!) for ten minutes to drain the capacitors, then reconnect and perform a proper idle relearn. If the code comes back immediately after a long run, then we talk about ECU repair specialists like ECU Testing in Derbyshire, which is miles cheaper than a brand-new unit from the dealer.
Can you drive with P0603?
Yes.
Urgency: medium.