What does it mean?
B1900 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Communication Circuit Error (BUS-OFF) .
Symptoms
- Several warning lamps on at once, including air bag, ABS and stability control
- Gauges dead, sweeping or showing implausible values
- Scan tool cannot communicate with one or more modules, or the whole network
- Vehicle may crank but not start, or start and run with severely reduced function
- Convenience functions such as central locking, mirrors and windows stop working together
Likely causes
- CAN high and CAN low shorted together, or one line shorted to ground or to battery voltage
- A failed module holding the bus dominant and flooding the network with errors
- Missing or failed terminating resistor inside one of the end modules
- Damaged bus wiring at a door boot, under a seat rail or where the loom passes through a bulkhead grommet
- Corroded or water damaged connector on a module in the network
- Low system voltage or a weak battery, which produces widespread communication faults
- Poor module power or ground connection
How to fix it
- Test the battery and charging system first, because low voltage alone can put modules into bus off
- Scan every module and list which ones respond and which are missing, since the pattern points to the section of the network at fault
- Measure resistance across the bus pins at the diagnostic connector with the ignition off; roughly 60 ohms indicates two healthy terminating resistors, 120 suggests one is missing and a very low value indicates a short
- Check the bus wires for shorts to ground and to battery voltage with the network unpowered
- Disconnect suspect modules one at a time and watch whether the bus resistance and communication return to normal, which isolates a module dragging the bus down
- Inspect the loom at door boots, seat rails and bulkhead grommets for chafing and repair with twisted pair matching the original
- Remove any aftermarket device connected to the bus and retest