Electrical system and control unitsGeneric OBD-II codeUrgency: Garage soon
Code P0600: serial communication link (CAN) fault
P0600 means: serial communication link: malfunction (the ECU loses communication with other modules).[1][2] The engine ECU has lost communication with, or control of, one or more modules in the car over the data network (normally the CAN bus). One source says it is logged after eight consecutive starts with the fault.[1][2]
What code P0600 means
The engine ECU has lost communication with, or control of, one or more modules in the car over the data network (normally the CAN bus). One source says it is logged after eight consecutive starts with the fault.[1][2]
It is a generic OBD-II code. It is considered a misleading code: it points to a communication and power supply problem, and not necessarily to a faulty ECU.[1][2]
Original definition (SAE J2012): Serial Communication Link Malfunction[1][2]
Causes of P0600
From most to least likely, according to the sources.
- 1Weak or discharged battery, or low supply voltage: the most common cause and the first to rule out.[1][2]
- 2Loose, rusty or poorly connected connectors at the ECU or other modules.[1][2]
- 3Poor earths at the ECU or modules.[1][2]
- 4Damaged, open or shorted CAN bus wiring, for example from chafing, bodywork repairs or rodents.[1][2]
- 5A faulty module elsewhere in the car (gearbox, ABS, body) disrupting the whole network.[2]
- 6Internal or software fault in the ECU: this is less common.[1][2]
Symptoms
- Engine warning light on, almost always with other stored codes.[1][2]Engine warning light: faults that cause it
- ABS and traction control lights on at the same time.[1][2]ABS/ESP light: faults that cause it
- Limp mode with limited power and an unresponsive accelerator.[2]Limp mode: faults that cause it
- Intermittent starting or a car that will not start.[1][2]Hard to start: faults that cause it
- Stalling at idle or rough running.[1][2]Engine stalls: faults that cause it
- Strange behaviour from the instrument cluster or an automatic gearbox that engages abnormally on some models.[2]Electronic warnings: faults that cause it
How to diagnose P0600
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the codes from all modules, not just the engine. Accompanying codes, for example U0100, show which module has stopped communicating.[1][2]
- 2Check the battery with a load test and the charging voltage: low voltage alone can trigger this code.[1][2]
- 3Inspect the connectors of the ECU and the modules: corrosion, bent pins or plugs that are not fully seated. Wiggle the wiring harness while watching live data to find intermittent faults.[2]
- 4Check the earths of the ECU and of the related modules.[1][2]
- 5Measure the continuity of the wiring between the module and the ECU. Only if everything is correct should the ECU be suspected; it is also worth looking for manufacturer software bulletins, as some cases are resolved with an update.[1][2]
Can I keep driving with P0600?
Garage soon
One source warns that P0600 can disable the ABS and traction control, and that driving like this can be dangerous. It may come with limp mode, stalling or starting failures, so it should be checked as soon as possible.[1][2]
Documented faults related to P0600
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.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- High severityFrequency: OccasionalM264/M254Poorly tightened 48 V earth wiring in the mild-hybrid system (fire risk)Mercedes-Benz has issued several recalls (2022-2025) because the 12 V and 48 V earth connections of some cars with a 48 V system may be poorly tightened: resistance rises, the connection heats up and a fire cannot be ruled out. The official workshop checks them and repairs them if necessary in an hour or more.
- High severityFrequency: Occasional1.9 TDIUnit injector tappet wear and injector wiring damageOn the unit injector system, the tappets that operate the injectors can wear if the oil is not changed on time, and the injector wiring can be damaged by contact with oil, causing misfires or loss of power.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
Frequently asked questions
What does code P0600 mean?
That the engine ECU is unable to communicate properly with one or more modules in the car over the data bus. It does not by itself indicate which module is at fault.[1][2]
Does the ECU need replacing with a P0600?
Almost never as a first step. The usual culprit is a weak battery, a poor connector or earth, or a wiring fault. The ECU is suspected last, after ruling out everything else.[1][2]
Can I drive with P0600?
With care and only as far as the garage: it may come with the ABS and traction control disabled, limp mode or stalling.[1][2]
What other codes often appear with P0600?
Network U0xxx codes, such as U0100, and other internal control module codes (P0601 to P0607), which help locate the source.[1][2]
Will I pass the MOT with code P0600?
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.
- P0600 – CAN data bus -malfunctionTroubleCodes.net · Technical documentation · consulted 29 October 2026
- P0600: Serial Communication Link Malfunctioncarfaultcodes.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