Electrical system and control unitsGeneric OBD-II codeUrgency: Garage soon
Code U0151: loss of communication with the airbag control unit
U0151 means: loss of communication with the restraint systems control module (airbag control unit).[1][2][3][4] Another module in the car (the network gateway or another monitoring module) has stopped receiving the periodic messages from the restraint systems control module (RCM), the airbag control unit. According to the German workshop Dietrich, the code only reports that the data connection has been interrupted: it does not say that a particular airbag or pretensioner has failed.[1]
What code U0151 means
Another module in the car (the network gateway or another monitoring module) has stopped receiving the periodic messages from the restraint systems control module (RCM), the airbag control unit. According to the German workshop Dietrich, the code only reports that the data connection has been interrupted: it does not say that a particular airbag or pretensioner has failed.[1]
In the TaT description (based on Ford), the code is stored when a module does not receive valid CAN messages from the RCM within a calibrated time with the ignition on, which points to a loss of communication on the network or to a power or earth fault that prevents the RCM from operating on the CAN network. Dietrich adds that an occasional entry with freeze frame data suggests an intermittent fault (for example, a contact that depends on vibration or temperature), and a permanent entry a continuous interruption.[1][3]
It is a generic network code (DTCSearch classifies it as controlled by ISO/SAE), so it means the same on any brand. CódigosDTC lists it with the Ford, Lincoln and Mercury brands in its definition.[2][4]
Original definition (SAE J2012): Lost Communication With Restraints Control Module[1][2][3][4]
Causes of U0151
From most to least likely, according to the sources.
- 1Connector under the seat (contacts for seat occupancy detection, side airbags and seatbelt pretensioners) loose or corroded. Dietrich considers this the most common cause.[1]
- 2Water or moisture ingress (through seals, blocked drains or spilt liquids) corroding the pins and plates.[1]
- 3Data line between the gateway and the airbag control unit interrupted or short-circuited, with sections of the harness chafed; RCM wiring in poor condition or damaged connections in its circuit (CódigosDTC).[1][2]
- 4Lack of power or earth to the airbag control unit: Dietrich warns that an earth fault gives the same symptoms as a faulty control unit.[1][3]
- 5Faulty airbag control unit, only after power, earth and wiring have been checked. Dietrich adds that the crash counter, triggered after an accident, can prevent communication.[1][2]
Symptoms
- Airbag warning light on in the instrument panel, usually while the code is active.[1][2]Airbag light: faults that cause it
- Engine fault warning light on (CódigosDTC).[2]Engine warning light: faults that cause it
- The code returns after clearing if the communication fault persists; it may be intermittent.[1]
How to diagnose U0151
In order: from the most likely and cheapest to check to the most expensive.
- 1Read all the control units and see which ones report the airbag control unit as unreachable: that will tell you whether a single module or a whole branch of the bus is at fault. Check the model's technical bulletins.[1][2]
- 2Measure the power supply and earth of the airbag control unit. Dietrich points out that an earth fault gives the same symptoms as a faulty module.[1]
- 3Inspect the connectors, especially under the seats: corrosion, open contacts and moisture. Check the wiring and repair anything worn or burnt.[1][2]
- 4Measure the voltages on the airbag control unit circuit and compare them with the permitted ranges; if they are outside, check whether the connections are the cause and repair them.[2]
- 5Check the signal quality on the data line with an oscilloscope.[1]
- 6On a car that has been in an accident, read the crash counter. Dietrich only considers the control unit at the end, after everything else, and warns that replacing it without proving the cause is expensive and often useless. After repair, clear the fault memory and reset the system if the warning light stays on.[1]
Can I keep driving with U0151?
Garage soon
Only one of the sources gives its view on severity: the Dietrich workshop advises against driving with the code active, because the restraint system may be disabled or may not deploy in an accident, and asks for the airbag warning light to be treated as a priority. The car can move, but the prudent course is not to postpone the check, and not to clear the code without correcting the fault, as it will reappear.[1]
Documented faults related to U0151
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Airbags: the most serious faults by engine and car
- Critical severityFrequency: Very frequentMercedes-Benz Clase A W176Takata airbags with a defective inflatorYes: A-Class cars built up to 2016 fall under the European programme to replace Takata airbag inflators, which can degrade with humidity and heat and fragment when deployed.
- Critical severityFrequency: Very frequentMercedes-Benz Clase C W205Takata airbags on the first vehicles (2014-2016)C-Class vehicles built up to 2016, including the first W205s, fall under the Takata airbag inflator replacement programme; the inflators can degrade with humidity and heat and fragment when deployed.
- Critical severityFrequency: Very frequentPeugeot 208 IIWindscreen trim clip incorrectly fitted, a risk with the curtain airbag (2023 production)On Peugeot 208 IIs built between June and November 2023, a windscreen trim clip may be fitted rotated by 180 degrees; if the curtain airbag deploys, that trim could come loose.
- Critical severityFrequency: Very frequentSeat AronaThe front passenger airbag gas generator can rupture and project fragmentsYes, on 2022-2025 cars: campaign 69U1 affects Arona cars built between 21 September 2022 and 7 April 2025. The housing of the front passenger airbag gas generator can rupture or release fragments when it deploys, with a risk of serious injury. The inspection and, where necessary, the replacement are free.
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.
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.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Main relay of the power relay assembly (overheating and fire risk)Yes, on the first units: Hyundai and Kia recalled 2016–2018 Ioniq and Niro hybrids and plug-in hybrids because the main relay that connects the high-voltage battery could come loose, overheat and, in the worst case, cause a fire.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Clutch hydraulic actuator (HCA): leak or moisture with risk of short circuit and fireYes, this is the most documented hybrid system fault: the hydraulic actuator that engages the combustion engine with the hybrid assembly has had two recalls (2018 for a leak on the Niro and 2025 for moisture in its electronic board on the Niro, Ceed and XCeed PHEV), with a risk of short circuit and fire.
- 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.
- 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.
U0151 by make
Documented faults that can trigger U0151 in each make's engines and cars.
- U0151 on Mercedes-Benz30
- U0151 on Volkswagen30
- U0151 on BMW27
- U0151 on Škoda22
- U0151 on Toyota22
- U0151 on Audi20
- U0151 on Opel17
- U0151 on Seat16
- U0151 on Fiat12
- U0151 on Volvo11
- U0151 on Citroën9
- U0151 on Ford9
- U0151 on Honda9
- U0151 on Mazda8
- U0151 on Renault8
- U0151 on Land Rover7
- U0151 on Nissan7
- U0151 on Jeep6
- U0151 on Peugeot6
- U0151 on Alfa Romeo5
- U0151 on Jaguar5
- U0151 on Suzuki5
- U0151 on Chevrolet4
- U0151 on Kia4
- U0151 on Lancia4
Frequently asked questions
Does U0151 mean my airbags do not work?
The code only says that communication with the airbag control unit has been lost, not that a particular airbag has failed. Even so, Dietrich warns that the restraint system may be disabled or may not deploy in an accident while the code is active, so the check should not be postponed.[1]
What is the most common cause?
According to Dietrich, the connector under the seat (occupancy detection, side airbags and pretensioners), which loosens or corrodes; then moisture and chafed or cut data cables. The airbag control unit is the last thing suspected.[1]
Should I replace the airbag control unit?
Not without first proving the cause: Dietrich warns that it is an expensive part and that replacing it is often useless if the problem is in the power supply, the earth or the wiring. First, the power, the earth and the connectors are measured.[1]
Why does the code come back after clearing it?
Because clearing does not fix the communication fault. If the problem persists, the control unit stores it again.[1]
Will I pass the MOT with code U0151?
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.[5]
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.
- Fehlercode U0151: Lost Communication with Restraints Control Module (Airbag)Kfz-Meisterbetrieb Dietrich · Other source · consulted 31 October 2026 · in German
- U0151 - Se ha perdido la comunicación con el módulo de control de los sistemas de retenciónCódigosDTC · Technical documentation · consulted 31 October 2026 · in Spanish
- U0151 - Lost Communication With Restraints Control ModuleThe Automotive Technician (TaT) · Technical documentation · consulted 31 October 2026
- U0151 - Lost Communication With Restraints Control ModuleDTCSearch · Technical documentation · consulted 31 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