What does it mean?
B1957 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear MICU Lost Communication with Combination Switch Control Unit (HLSW Message) .
Symptoms
- Headlamps, side lights or automatic lighting not responding to the stalk
- Lights stay on or come on by themselves because the last known state is used
- High beam, flash to pass or fog lamps behave inconsistently
- Other stalk driven functions such as turn signals or wipers affected at the same time
- Multiple lost communication codes stored across modules
Likely causes
- Open or shorted communication wire between the column switch unit and the rear control unit
- Combination switch control unit connector loose or corroded, often disturbed during column, clockspring or airbag work
- Power or ground missing at the column switch unit because of a blown fuse or a broken supply wire
- Water entry down the steering column or through the bulkhead grommet corroding the connector
- Internal failure of the combination switch control unit
- Weak battery or heavy voltage drop during cranking causing the unit to drop off the network
- Rear control unit receiver fault or corrosion inside the unit
How to fix it
- Confirm the complaint by working the light stalk through every position while a helper watches the lamps
- Scan all modules and check whether other units also report losing the same transmitter, which narrows the search
- Check battery voltage and the fuses feeding the combination switch control unit
- Back probe power and ground at the column switch unit, then measure the voltage drop on the ground under load
- With both units unplugged, test the communication wire for continuity and for shorts to ground and battery, flexing the harness at the bulkhead
- Inspect the connectors under the column for corrosion, moisture and pushed back terminals
- Repair the wiring or connector, retest, and only replace the combination switch control unit if it stays silent with good power, ground and wiring