Electrical system and control unitsGeneric OBD-II codeUrgency: Garage soon
Code P0601: ECU memory checksum error
What code P0601 means
The ECU runs a self-test of its internal memory every time it is switched on. If the checksum of the stored data does not match the expected one, it logs P0601: the programming data may be corrupted.[1][2]
According to the sources, it can be caused by damaged programming, an unstable power supply or a physical fault in the ECU. It is a generic OBD-II code.[1][2]
Original definition (SAE J2012): Internal Control Module Memory Check Sum Error[1][2]
Causes of P0601
From most to least likely, according to the sources.
- 1Poor power supply or earth: a weak battery or an unstable alternator can upset the memory check. It is the cheapest cause and the first to rule out.[1][2]
- 2ECU connectors that are corroded, loose or wet.[2]
- 3Interrupted update or reprogramming, for example after a reflash or remap during which power was lost.[1][2]
- 4Voltage spikes, such as those from a badly done jump start or a faulty alternator.[2]
- 5Moisture inside the ECU or an internal memory fault (cracked solder joints or a damaged chip); this usually means replacing or repairing the ECU.[1][2]
Symptoms
- Engine warning light on, sometimes with no other symptoms.[1][2]Engine warning light: faults that cause it
- The engine starts and stops straight away, or turns over but will not start.[1][2]Hard to start: faults that cause it
- Limp mode with greatly reduced power.[2]Limp mode: faults that cause it
- Random stalling, especially with a warm engine.[1][2]Engine stalls: faults that cause it
- ABS or traction control lights on, because the ECU communicates with those systems.[2]ABS/ESP light: faults that cause it
How to diagnose P0601
In order: from the most likely and cheapest to check to the most expensive.
- 1Check the battery and charging system first of all: a battery load test and a stable charging voltage. Low voltage is a typical cause of false alarms.[1][2]
- 2Read all stored codes: the presence of P0602, P0603 or P0604 helps distinguish a programming fault from a physical one.[2]
- 3Inspect the ECU connectors and earths: corrosion, bent pins, signs of water.[2]
- 4Confirm that the ECU receives a clean voltage at its power pins (about 12 to 14.5 V with the engine running).[2]
- 5If the code returns after clearing it and the power supply is correct, the ECU needs repair or replacement, with subsequent programming to the car's VIN and options.[1][2]
Can I keep driving with P0601?
Garage soon
According to the sources, the effect ranges from no symptoms at all to stalling, failure to start or limp mode. An ECU that will not start can leave the car stranded, so it should be diagnosed soon.[1][2]
Documented faults related to P0601
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 P0601 mean?
That the ECU has detected an error in the checksum of its internal memory, which indicates that the programming data may be damaged.[1][2]
Is it always a faulty ECU?
No. The sources point out that many cases come from poor voltage or earth, and that this is the first thing to rule out before spending money on an ECU.[1][2]
Can I clear the code and carry on?
If it was a one-off fault it may not return, but if it reappears immediately after clearing it, the error persists and needs diagnosis.[1]
How much does it cost to fix?
It depends entirely on the cause: from a battery or a connector to a new or repaired and programmed ECU. One source estimates £400 to £2,000 in the UK in the most serious cases; we have no reliable reference for Spain.[1]
Will I pass the MOT with code P0601?
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.
- P0601 Code: PCM memory checksum errorCarista · Technical documentation · consulted 29 October 2026
- P0601: Internal Control Module Memory Check Sum 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