What does it mean?
B2106 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Ignition Run/Start Control Circuit Open .
Symptoms
- Cluster warning lamp or message, the code often sets the moment the key is turned
- Feature controlled by that input is completely inoperative rather than erratic
- Engine will not crank, or cranks only in one key position, when the ignition circuit is involved
- Adjustable pedals, memory or cruise functions locked out
- Fault stays stored and comes straight back after a clear
- Occasional blown fuse if the circuit is shorted to a hot feed
Likely causes
- Signal wire shorted to battery voltage or to the 5V reference by chafing against an adjacent circuit
- Open sensor ground, which lets a pull up resistor inside the module drive the input to full scale
- Open circuit in the ignition run/start feed, from a blown fuse, broken wire or unplugged connector
- Burnt or pitted contacts inside the ignition switch that no longer pass the run/start signal
- Corroded connector pins creating enough resistance to look like an open to the module
- Position sensor with a worn or burnt resistive track that outputs maximum voltage
- Damaged harness where it passes a metal edge, bracket or the steering column
- Failed body control module input (check only after the wiring is proven good)
How to fix it
- Confirm the manufacturer definition and the correct pin for this application
- Check the fuses that supply the circuit and the ignition switch feeds before anything else
- Measure voltage on the suspect circuit with the sensor or switch unplugged, key on: full battery voltage points to a short to battery
- Check the sensor ground for continuity to a known good chassis ground, a few tenths of a volt drop is already too much
- Perform a voltage drop test across the ignition switch in each key position
- Ohm the harness end to end with both connectors off to find an open circuit
- Inspect the harness at every bracket, grommet and pass through where the loom can rub
- Repair or replace the wiring, switch or sensor, then verify live data reads within range in all key positions