B1559

Code

Other B — Body

Door Lock Cylinder Circuit Failure

Brand: Other

Type: B — Body

Views: UK: 31 EN: 41 RU: 25

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Page language: EN

Causes

Open or short in wiring between door lock cylinder and BCM
Corroded, pushed-out, or damaged connector at the door lock cylinder
Failed door lock cylinder switch or internal contact wear
Faulty door lock actuator or integrated switch (if combined)
Poor ground or power supply to the circuit
Blown fuse or fusible link for door lock circuit

Symptoms

Key cylinder fails to lock/unlock door(s) with mechanical key
Intermittent or no response from door locks when using key
Door lock indicator or message on dash (if equipped)
Related alarm or central locking functions may not operate
DTC present in BCM and locking may be limited to remote fob only

What to check

Retrieve freeze frame and any related DTCs with a scan tool; clear code and see if it returns
Visually inspect door lock cylinder, surrounding trim, and connector for corrosion, damage, or water
Inspect door wiring harness at hinge (door jamb) for broken/chafed wires
Check related fuses and relays for continuity and correct condition
Backprobe the door lock cylinder connector while actuating the key to observe signal behavior
Wiggle test wiring while observing scan tool or meter for intermittent changes

Signal parameters

Typical key cylinder signal: switched to ground or +12 V when rotated (depends on design)
Resting voltage: 0–0.5 V (ground) or battery voltage depending on circuit design; switching to opposite state on operation
When shorted: near 0 Ω or near battery voltage when short to power/ground present
Open circuit: infinite resistance between cylinder switch terminal and BCM input
Expected switching frequency: single event per key rotation (not PWM)

Diagnostic algorithm

Connect a scan tool. Record B1559 and any related codes; clear codes and attempt to re-create.
Perform a visual inspection of the cylinder, connector, and door harness, especially at the hinge/boot. Repair obvious damage.
Check fuses and relays feeding the lock circuit. Replace if blown or intermittent.
Backprobe the lock cylinder connector. With key rotated, observe voltage change relative to chassis ground. Note behavior (stable, intermittent, no change).
Measure continuity/resistance between the cylinder switch terminal and the BCM input pin with connectors disconnected. Expect near 0 Ω when closed, infinite when open depending on switch state.
Wiggle the harness at the door jamb while observing voltage/continuity to find intermittent faults. Repair or replace broken wires or connectors.
If wiring and switch check good, bench-test or swap a known-good lock cylinder or actuator (if available) to confirm component failure.
Inspect for water intrusion or corrosion in the cylinder assembly; clean or replace as required.
If all wiring and components verify OK, check BCM inputs for damage. Test BCM grounds/power. Replace BCM only after excluding wiring and components.
After repairs, clear codes, cycle locks multiple times, and road test to confirm code does not return.

Likely causes

Corroded connector or pin(s) at the lock cylinder
Broken or chafed door harness (door jamb flex point)
Failed microswitch inside the lock cylinder assembly
Intermittent connection due to moisture or dirt in the cylinder
Failed BCM less likely but possible after wiring and component checks

Fault status

⚠️ Status

Stored when the body control module detects an abnormal condition (open, short, intermittent signal, or out-of-range voltage) on the door lock cylinder input circuit. Prevents reliable detection of key cylinder position and may disable cylinder-based locking/unlocking.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours