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Home / DTC / B2100 — Door Driver Key Cylinder Switch Failure

B2100 — Door Driver Key Cylinder Switch Failure

Detailed page for trouble code B2100.

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Code

B2100

Other B — Body

Door Driver Key Cylinder Switch Failure

Brand: Other
Type: B — Body
Views: UK: 21 EN: 51 RU: 38
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Page language: EN

Causes

  • Failed key cylinder switch (worn or internally broken)
  • Open, shorted or corroded wiring/connector at the switch
  • Poor ground or battery supply to the circuit
  • Contaminated or seized key cylinder preventing switch actuation
  • Faulty body control module (BCM) or input circuit
  • Intermittent mechanical linkage or connector damage

Symptoms

  • DTC B2100 stored and possibly a related dash message
  • Mechanical key lock/unlock does not operate power locks reliably
  • Driver door lock/unlock only works intermittently or not at all
  • Interior lights or courtesy functions not working correctly
  • Key cylinder position not recognized by vehicle (no response from BCM)

What to check

  • Read stored codes and freeze-frame data with a scan tool; note when code sets and any related codes (BCM or network codes).
  • Visual inspection of driver door key cylinder, switch, connector and wiring for corrosion, physical damage or water ingress.
  • Inspect door jamb harness for chafing, broken wires or damaged grommets.
  • Check connector pins for pushed-out or bent terminals and for corrosion.
  • Verify battery voltage at the switch connector and check for good ground.
  • Operate the mechanical cylinder while monitoring the switch signal with a DVOM or scope.

Signal parameters

  • Expected: switch toggles between two states when key is turned (commonly near 0 V and battery voltage ~12 V).
  • Some systems use a ground-switched input; expected state change is between open/closed or 0 V/near-battery voltage.
  • When idle, steady voltage or open-circuit per manufacturer spec; when actuated, voltage should change within milliseconds.
  • Typical continuity: near 0 ohms when closed, open/infinite ohms when open — check against vehicle-specific values.

Diagnostic algorithm

  1. Use a scan tool to confirm B2100 and record any related codes. Note conditions under which the code was set (key position, door open/closed).
  2. Visually inspect the key cylinder assembly and connector for corrosion, water, bent pins or mechanical damage. Repair visible issues.
  3. With connector unplugged, check for battery voltage on the power supply terminal and for a reliable ground on the harness side per the wiring diagram.
  4. Backprobe the switch signal wire. Operate the key cylinder and observe the signal with a multimeter or scope — verify the input changes state cleanly each time the cylinder is turned.
  5. Perform a continuity check of the signal wire from the key cylinder connector to the BCM connector (with doors open/closed and while flexing the harness at the door jamb) to find intermittent breaks.
  6. If wiring and connector are good, bench-test or substitute the key cylinder switch (if serviceable) to confirm switch failure.
  7. If switch replacement fixes the symptom, install new switch and secure connectors; clear codes and retest multiple actuations and vehicle cycles.
  8. If switch and harness test good but code remains, inspect BCM input circuit for damage and check for other network or module faults. Consider module replacement or repair only after confirming input fault and following manufacturer procedures.
  9. After repair, clear codes and verify no recurrence under the original conditions (cool/wet conditions if relevant).

Likely causes

  • Corroded connector or pin(s) at the driver door key cylinder
  • Switch contacts worn or stuck due to moisture/contaminants
  • Broken wire in the door harness (pins broken at door jamb)
  • Switch not making contact because of mechanical misalignment
  • BCM input circuit failure (less common)

Fault status

⚠️ Status
Driver door key cylinder switch circuit failure detected. Input not changing or out-of-spec signal to BCM; intermittent or open/short condition present.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-1.5 hours

Similar codes

B2101 B2102 B2103 B2104 B2105
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