Airbags

U0172 — Lost Communication with Occupant Classification Module (OCS)

Severity: medium Drive with care, to a shop

What U0172 means

The airbag (SRS) control unit is no longer receiving messages from the occupant classification module over the CAN bus. That module uses a sensor in the seat to tell whether the seat is empty or holds an adult or a child, which decides if the passenger airbag should deploy in a crash. Without that data, the system usually switches the passenger airbag off as a precaution.

Symptoms

  • Airbag (SRS) warning light is on
  • Passenger airbag off indicator is on or flashing
  • Passenger airbag indicator doesn't match who is actually seated
  • Other warning lamps may also come on
  • Functions of the affected module are unavailable

Possible causes

  1. Failed occupant sensing mat in the passenger seat
  2. Connector under the seat unplugged or loose
  3. CAN bus wiring fault: open, short or chafed harness
  4. Corrosion on connectors or terminals
  5. Power supply or ground fault at the OCS module
  6. Another faulty module disrupting the CAN bus
  7. Harness pinched or disturbed under the seat after cleaning or repairs

How to diagnose

  1. Scan all modules and note which ones are not communicating on the bus
  2. Check for other U-codes and SRS codes, and see whether U0172 returns after clearing
  3. Inspect the connector and harness under the passenger seat for looseness, damage and corrosion
  4. Check power and ground at the OCS module using the wiring diagram
  5. Measure CAN bus resistance and voltages at the diagnostic connector
  6. Look for chafed or broken wires along the seat harness
  7. If the bus is healthy, test the OCS sensor and module using the manufacturer procedure
  8. Disconnect suspect modules one at a time only per a documented procedure, after disconnecting the battery and waiting the specified SRS time

Common fixes

  • Repair or replace the damaged connector or wiring
  • Clean corroded terminals
  • Restore power or ground to the module
  • Replace the OCS module or mat, then calibrate or program it as required
  • Replace a faulty module that is loading the CAN bus

Questions and answers

What does U0172 mean?

It means the airbag control unit lost communication with the occupant classification module. The system can't tell who is in the passenger seat and usually disables that airbag.

Will the passenger airbag deploy with U0172 set?

Probably not, because the system turns it off when seat status is unknown. Get it repaired, and keep passengers, especially children, out of the front seat meanwhile.

Can I fix U0172 myself?

You can check the connector and harness under the seat. Airbag work requires disconnecting the battery and extra care, so see a shop if you're unsure.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.