What does it mean?
B1557 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Application specific integrated circuit .
Symptoms
- Module stays powered after the key is removed and the battery is flat by morning
- Accessories, lighting or wipers remain live with the ignition off
- Warning chimes or dash lamps stay on after the driver leaves the vehicle
- Engine is difficult to shut down or the immobiliser does not arm
- The code sets again within seconds of being cleared
- On the internal fault variant, the module responds unpredictably and several body functions fail together
Likely causes
- Run/start input wire chafed against a constant 12 V feed, so the module sees the ignition on with the key removed
- Ignition switch contacts sticking or welded, keeping the run circuit live
- Aftermarket remote starter or alarm spliced into the ignition feed and back-feeding it
- Failed diode or relay in the circuit allowing voltage to feed backwards from another circuit
- Connector terminal displaced onto a powered pin behind the dash
- Damaged input clamp inside the module after a previous voltage event
- On applications where this code reports an internal fault, a failed integrated circuit inside the module itself
How to fix it
- With the key off, measure the run/start input at the module; any battery voltage present there identifies the failing side of the circuit
- Unplug the ignition switch and re-measure: if the voltage disappears the switch is at fault, if it remains the harness is shorted
- Check aftermarket remote start or alarm wiring at the ignition harness first, as these taps are a frequent cause
- Inspect the loom behind the steering column and along the fuse box for insulation worn through onto a powered wire
- Test any relay or diode in the circuit for back-feed with the relay removed
- Replace the ignition switch if its contacts hold after the key is released; repair the harness before touching the module
- Where the code reports an internal module circuit fault, verify supply, ground and software level, then follow the manufacturer procedure for reprogramming or replacement