B2721

Code

Generic B — Body

Door Lock Actuator Circuit Malfunction - Rear Left

Brand: Generic

Type: B — Body

Views: UK: 8 EN: 9 RU: 9

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Page language: EN

Causes

Open or short in the rear left door lock actuator wiring (power or ground)
Corroded/loose connector at the door or body harness
Failed door lock actuator motor or internal gears (mechanical seizure)
Blown fuse or fusible link for door locks
Faulty door latch/lock switch or keyless entry receiver
Faulty BCM/door control module output driver

Symptoms

Rear left door does not lock or unlock with key fob, door switch, or central locking
Intermittent operation of rear left lock (works sometimes)
Clicking or buzzing noise from inside the door or no sound at all
Other doors operate normally (isolated to rear left)
Related door ajar or security warning/message illuminated

What to check

Scan vehicle and confirm B2721 is present; record freeze frame and related codes
Operate locks (key fob, door switch, BCM command) while listening at the rear left door
Visually inspect door harness, boot/grommet, and connector for damage, corrosion or water
Check fuse(s) for door locks and any related power supplies
Backprobe actuator connector and observe voltage/ground while commanding lock/unlock
Wiggle wiring harness through full door travel to reproduce intermittent faults

Signal parameters

Supply voltage at actuator connector when commanded: approx. battery voltage (nominal ~12 V); should not drop below ~9 V during operation
Motor coil resistance (typical range): a few ohms to low tens of ohms (manufacturer-specific)
Current draw when operating: usually under 5–10 A peak for small motors; excessive current suggests binding or short
BCM output: switched ground or switched +12 V (probe to identify), may be PWM-driven — check for switching frequency and duty cycle when commanded
No voltage when not commanded (open circuit) and stable low resistance across motor terminals when disconnected

Diagnostic algorithm

Verify code and related DTCs. Clear codes and attempt to re-create fault by commanding lock/unlock several times while monitoring behavior.
Perform a visual inspection of the rear left door wiring, connector, and grommet. Look for chafing, corrosion, or water ingress.
Check relevant fuses and relays for the door lock circuit. Replace any blown items and re-test.
With the door open, backprobe the actuator connector. Command lock and unlock; verify supply and return switching (voltage present and switching to ground or vice versa).
If no voltage switching from module, check for power feed and ground upstream (fuse, splice, connector). Repair any open circuits.
Measure actuator motor resistance with connector disconnected. Compare to expected range; a shorted or open winding indicates actuator replacement.
If resistance is normal, apply a fused 12 V test directly to the actuator (briefly) to verify mechanical movement. If it moves, the actuator is OK and the fault is in wiring or module output.
If actuator draws excessive current during direct power test or binds, replace actuator assembly and retest.
If actuator does not move with direct power but resistance looks normal, inspect internal gears/latching mechanism and replace assembly if mechanically faulty.
If actuator fails to operate with correct commands but direct power works, investigate BCM/door module output driver — check for intermittent short or damaged driver circuit. Consider module replacement only after confirming wiring and actuator are good.
After repairs, clear codes and perform multiple lock/unlock cycles and full door travel checks to ensure fault does not return.

Likely causes

Corroded or pinched connector in the rear left door harness
Failed actuator motor (common)
Open or shorted ground or power feed to the actuator
BCM/door module output transistor weak or failed
Mechanical binding in lock assembly preventing motor movement

Fault status

⚠️ Status

B2721 — Door Lock Actuator Circuit Malfunction (Rear Left). The control module detected abnormal behavior in the rear left door lock circuit (open/short/high current or no response). Verify wiring, connectors, actuator, fuses, and module outputs.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours