U0170
Lost Communication With "Restraints System Sensor A"
- Severity
- Critical
- Driving
- Short journeys only
The control module has stopped receiving messages from restraints system sensor A, which is part of the airbag and seatbelt pretensioner system. The car drives completely normally and there is nothing to feel - but the restraint system has faulted, and airbags may not deploy in a collision. The airbag warning light will be on, and in most jurisdictions that alone is an inspection failure.
Possible causes
- CommonLow battery voltage or a discharged battery, dropping modules off the bus
- CommonConnector under a seat disturbed by seat movement, cleaning or fitting a child seat
- CommonCorroded or water-ingressed connector - footwell connectors suffer from wet carpets
- CommonDamaged, chafed or corroded bus wiring
- PossibleBlown fuse or corroded earth on the supply to restraints system sensor A
- PossibleFailed module or sensor
- PossibleModule not coded or configured after a previous repair or replacement
- PossiblePrevious accident damage, or a module never replaced after deployment
What you might notice
- Airbag warning light on and staying on
- Passenger airbag status indicator wrong or blank
- Seatbelt warning behaving oddly
- No effect on how the car drives - this is the point, the fault is silent
What to check, in order
- Get this repaired before relying on the car for normal driving. It does not affect control of the vehicle, so short journeys to a garage are reasonable, but the protection you are counting on in a crash is not currently there.
- Check battery voltage and state of charge before anything else. A weak or failing battery drops modules off the bus and sets lost-communication codes with no wiring fault at all - this is the single most common false lead in this whole family.
- Check whether this code is current or historic. Lost-communication codes are routinely set by a flat battery, a jump start or a battery disconnection, and a historic code straight after one of those events usually records the event rather than a fault.
- Ask what happened just before the light appeared. Seats moved, carpets lifted, a child seat fitted or footwell electrics disturbed will account for most of these codes, and the connector under the seat is where to look.
- Inspect the yellow restraints connectors for corrosion, water and a locking tab that has not clicked home.
- Note how many U-codes are stored. Several at once points at battery, earth or bus wiring, not at several modules failing simultaneously.
- Check the module has not simply been left un-coded after a previous repair.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
U00xxU01xxU02xxU03xxU04xxU05xxU06xxU07xxU08xxU09xxU0AxxU0BxxU0CxxU0DxxU0ExxU0FxxU10xxU11xxU12xxU13xxU14xxU15xxU16xxU17xxU18xxU19xxU1AxxU1BxxU1CxxU1DxxU1ExxU1FxxU20xxU21xxU22xxU23xxU24xxU25xxU26xxU27xxU28xxU29xxU2AxxU2BxxU2CxxU2DxxU2ExxU2FxxU30xxU31xxU32xxU33xxU34xxU35xxU36xxU37xxU38xxU39xxU3AxxU3BxxU3CxxU3DxxU3ExxU3Fxx
Network communication
U0100U0101U0102U0103U0104U0105U0106U0107U0108U0109U0110U0111U0112U0113U0114U0115U0116U0117U0118U0119U0120U0121U0122U0123U0124U0125U0126U0127U0128U0129U0130U0131U0132U0133U0134U0135U0136U0137U0138U0139U0140U0141U0142U0143U0144U0145U0146U0147U0148U0149U0150U0151U0152U0153U0154U0155U0156U0157U0158U0159U0160U0161U0162U0163U0164U0165U0166U0167U0168U0169U0170U0171U0172U0173U0174U0175U0176U0177U0178U0179U0180U0181U0182U0183U0184U0185U0186U0187U0188U0189U0190U0191U0192U0193U0194U0195U0196U0197U0198U0199