Left rear window motor circuit open

What B2226 means

BYD's body control architecture uses a central Body Control Module (BCM) or a distributed Door Control Unit (DCU) to manage power window motors. B2226 is stored when the BCM or rear-left DCU detects a break in the left rear window motor circuit — meaning current cannot flow through the motor winding when commanded. On BYD Han, Tang, Song, and Atto models, each door typically has its own door control unit that communicates with the main BCM via the CAN body bus. The rear-left window motor is powered and monitored by the rear-left DCU (or the BCM directly on simpler architectures). An open circuit means the motor winding has failed internally, the connector has come apart, or the wiring between the controller and motor has broken. On BYD EVs, the body network faults can be intertwined with the high-voltage system status — the 12V body network remains active even when the traction battery is isolated, so window faults are diagnosed in the same way as on conventional vehicles.

Symptoms

• Left rear power window does not operate from any switch position (driver's master switch or rear-left local switch)
• B2226 stored in the BCM or body system fault log
• Other rear-left door functions (if sharing the DCU) may also be unresponsive
• No effect on driving, propulsion, or high-voltage battery systems
• Window stuck in an open or partially-open position presents a security and weather exposure risk

Common causes

• Failed left rear window motor — internal open winding is the most common cause, especially after high-cycle use or moisture intrusion into the motor housing
• Disconnected or damaged window motor connector — the connector at the door hinge area is a high-flex point that eventually fatigues and breaks
• Broken wiring in the door hinge flex zone — the wire loom passing through the rubber door boot between the B-pillar and rear door is subject to repeated flexing and eventual wire fatigue fractures
• Failed rear-left door control unit (DCU) — internal failure of the output driver stage for the window motor
• Water intrusion in the door causing corrosion of the motor connector or motor windings

Diagnostic approach

1. Test window operation from the driver's master switch and the rear-left local switch — If the window does not respond from either switch position, the fault is in the motor circuit or its power supply rather than in the switch itself. If it responds from the master but not the local switch, the local switch is the likely fault (but B2226 would not typically be set in that case — B2226 points to the motor circuit).
2. Inspect the wire loom at the door hinge flex area — Open and close the rear-left door several times while watching the rubber boot at the hinge — if it flexes severely, wires inside may be cracked. Remove the rubber boot and inspect the wiring bundle. Flex the wires manually while measuring continuity on the motor circuit; an intermittent open that appears during flexing confirms a fatigued wire.
3. Check voltage and ground at the window motor connector — Disconnect the motor connector and measure supply voltage with the window switch actuated — the BCM or DCU should send battery voltage to one motor terminal and ground to the other (reversing for up/down). If voltage is present at the connector but the motor does not run, the motor itself has failed. If voltage is absent, trace back to the DCU or BCM output.
4. Replace the left rear window motor if electrical supply is confirmed — BYD window motors are replaceable independently of the regulator assembly on most models. Remove the rear door trim panel (typically 4–6 clips plus 2 screws behind the pull handle), access the window regulator, and swap the motor. Clear B2226 after replacement and cycle the window through its full range of travel several times to confirm normal operation.

Make & model notes

BYD: BYD Han, Tang, and Atto 3 (2020+): the door control units on these models communicate over CAN body bus and are integrated into the door trim. A DCU that has experienced water ingress can generate multiple body codes including B2226 even when the motor itself is undamaged. Inspect the DCU's connector and housing for signs of moisture before condemning the motor.

BYD: BYD diagnosis requires a compatible OBD tool that supports BYD manufacturer protocols. Generic OBD-II readers will not access body module codes. BYD's proprietary DiLink diagnostic system can be accessed via compatible aftermarket tools (Launch X431, Autel MaxiSys) or through BYD dealerships using the official diagnostic software.

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