Electrical system and control unitsGeneric OBD-II codeUrgency: Monitor
Code P0603: ECU KAM memory error
P0603 means: internal control module: keep alive memory (KAM) error.[1][2] The ECU keeps a permanently powered memory, even with the ignition off ("keep alive"), where it stores what it has learned about fuelling, ignition and, on some cars, gear changes. P0603 indicates that this memory has failed its self-test.[1][2]
What code P0603 means
The ECU keeps a permanently powered memory, even with the ignition off ("keep alive"), where it stores what it has learned about fuelling, ignition and, on some cars, gear changes. P0603 indicates that this memory has failed its self-test.[1][2]
With this code the ECU works with default values instead of the learned ones. One of the sources notes that it appears very often when non-original engine management products have been fitted.[1][2]
Original definition (SAE J2012): Internal Control Module Keep Alive Memory (KAM) Error[1][2]
Causes of P0603
From most to least likely, according to the sources.
- 1Weak battery or corroded or loose terminals that do not maintain the constant voltage the memory needs.[2]
- 2Blown fuse in the ECU's permanent power supply, often because of a badly connected accessory.[2]
- 3ECU wiring that is damaged, corroded or has poor earths.[1][2]
- 4Non-original tuning products or remaps.[1][2]
- 5Water ingress into the ECU or ignition interference from poorly insulated leads.[1]
- 6Fault in the ECU itself: the least likely cause.[1][2]
Symptoms
- Engine warning light on; sometimes the only symptom.[1][2]Engine warning light: faults that cause it
- Long cranking, especially in the morning.[2]Hard to start: faults that cause it
- Intermittent stalling or engine jerking.[1]Engine stalls: faults that cause it
- Uneven idle when cold or hesitation when accelerating.[1][2]Jerking: faults that cause it
- Higher fuel consumption until the ECU learns again.[1][2]Uses more fuel: faults that cause it
How to diagnose P0603
In order: from the most likely and cheapest to check to the most expensive.
- 1Check the battery with a load test: over 12.4 V at rest and between 13.8 and 14.4 V with the engine running. A battery that collapses under load is a typical cause.[1][2]
- 2Clean and retighten the battery terminals and check the chassis earth cable.[1][2]
- 3Check the fuses on the ECU's permanent power supply and that no accessories have been spliced into those circuits.[2]
- 4Inspect the ECU wiring and connectors, and the spark plug leads if fitted, looking for damage, water or high-voltage leaks.[1][2]
- 5If the car has a remap or a tuning box, remove it and check whether the code disappears.[1][2]
- 6Only if everything above is fine, suspect the ECU or check whether there is a manufacturer software update.[1][2]
Can I keep driving with P0603?
Monitor
The ECU keeps working with default values, and the sources point to a mild effect: warning light on, somewhat long cranking or higher consumption. If stalling begins or the engine misfires, take it to a garage. The sources do not give a specific urgency.[1][2]
Documented faults related to P0603
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Control units and comfort electronics (BSI, SAM...): the most serious faults by engine and car
- High severityFrequency: CommonPeugeot 408Electronic faults with the doors, boot and screen (suspected BSI control unit)In 2025 Peugeot recalled around 60,000 2023-2024 Peugeot 308 and 408 cars (code MUV) over a software fault in the door control unit that can cause unintended opening or closing and disable the anti-trap protection on the windows; 408 owners also describe a power boot lid that will not open or close and a screen that goes black.
- High severityFrequency: CommonRenault Laguna IIMultiplex electrical system and hands-free card faultsThe Laguna II had a reputation problem because of faults in its multiplexed electrical network: the hands-free card, the card reader and the ABS, ESP and handbrake warning lights came on erratically, especially in the early years of production (2001-2003).
- Critical severityFrequency: OccasionalMazda MX-5 IVDC/DC converter control unit fault with risk of short circuit and fireA 2018 Safety Gate alert covers MX-5 ND models built between August 2014 and April 2017: the DC converter control unit could fail, cause a short circuit and damage the converter, with a risk of fire. It is a precautionary recall; check the chassis number at the official service centre.
- Medium severityFrequency: Very frequentFiat StiloElectrical and electronic faults in the multiplex systemThe Stilo has had a reputation for widespread electrical faults since its launch: poor contacts in the multiplex wiring, an instrument cluster that switches off and sensors that disconnect, sometimes while the car is running.
12 V battery: the most serious faults by engine and car
- Medium severityFrequency: Common2.0 and 2.5 HybridThe 12 V battery goes flat if the car sits unused for several daysYes, it is a common complaint: the 12 V battery can go flat after just a few days without using the car, because of the standby drain from the electronics (multimedia, telematics, keyless entry). With the 12 V battery very low, the hybrid system can lock itself into a safe mode.
- Medium severityFrequency: OccasionalE-Tech Híbrido12 V battery going flat or needing early replacementSeveral Clio, Arkana and Austral owners with the E-Tech engine document premature replacement of the 12 V auxiliary battery, in one case twice in the first year. It is not the most widespread fault of the system, but it appears repeatedly across different models.
- Medium severityFrequency: Occasional1.5 Hybrid12 V battery going flat while parkedYes: on the hybrid Yaris and Yaris Cross, the 12 V battery can go flat within a few days while parked because of the residual draw of modules such as eCall or keyless entry. It is fixed with a software update or, if the battery is already damaged, by replacing it.
- Low severityFrequency: OccasionalHonda e:HEV / i-MMD12 V battery going flat and hybrid system failing to startIf the car stands unused for a long time, the 12 V auxiliary battery can go flat and the hybrid system does not activate ("Ready" does not appear) even though the traction battery is charged. It is fixed by charging or replacing the battery.Repair (garage): €120–€250
- High severityFrequency: CommonHyundai Ioniq 5Faulty ICCU: 12 V battery drain and loss of drive powerThe Integrated Charging Control Unit (ICCU) can fail on the Ioniq 5: it drains the 12 V battery, may refuse to charge and, in the most serious cases, cause the car to lose power or not go into drive mode. Hyundai has replaced this part and updated its software on units built between January and February 2023.
- High severityFrequency: OccasionalBMW Serie 6 E63/E64Battery drain and loose positive cableThe battery and alternator are frequently cited by Fiches-auto, and there is a recall for the battery's positive cable, which can work loose.
Frequently asked questions
What does P0603 mean?
That the ECU's permanent memory (KAM), where it stores learned values, has failed its self-test.[1][2]
Can the light stay on with no other symptoms?
Yes. According to the sources, the warning light is often the first and only sign.[1]
Can a remap cause P0603?
Yes. The sources cite it as a very common cause; in those cases the code is neither fixed nor cleared until the product is removed.[1][2]
Does the ECU need replacing?
Rarely. First rule out the battery, terminals, fuses, wiring and earths, which are the most common causes.[1][2]
Will I pass the MOT with code P0603?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[3]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P0603 – Engine control module (ECM) -KAM errorTroubleCodes.net · Technical documentation · consulted 29 October 2026
- P0603: Internal Control Module Keep Alive Memory (KAM) Errorcarfaultcodes.co.uk · Technical documentation · consulted 29 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish