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Mirror Driver Switch Assembly Circuit Open

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Severity

Medium

Can I keep driving?

Usually drivable, but get it diagnosed without delay.

First step

Verify the fault first, repair second.

  • BBody
  • 1Manufacturer-specific
  • 5Body
  • 40Sequence number

What does it mean?

B1540 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Occupant classification-ECU malfunction .

Symptoms

  • Power mirrors do not respond to the driver switch at all, or move on one axis only
  • Mirror memory and folding functions are inoperative
  • Other functions sharing the same switch pack, such as window lock or mirror select, behave erratically
  • MIL (check engine lamp) stays off, but an airbag warning lamp may be lit where the code refers to the occupant classification system
  • The code returns as soon as the door is opened and closed a few times

Likely causes

  • Broken or corroded conductor in the driver door harness, most often inside the hinge boot where the loom flexes every time the door is opened
  • Water getting behind the door trim and corroding the terminals of the mirror switch assembly
  • Worn or burnt internal contacts inside the mirror switch itself
  • Loose, backed-out or spread pins at the switch or at the door module connector
  • Lost ground reference for the switch pack after previous door repair or an accessory installation
  • Failed input stage in the driver door module or body control module
  • On applications where this code is assigned to the occupant classification system, an internal fault or lost supply inside the OCS control unit

How to fix it

  1. Read the freeze frame data, note whether the fault is current or stored, then wiggle-test the door loom while watching the switch input in live data
  2. Inspect the mirror switch connector for water, green corrosion and pushed-back terminals; clean and re-seat before replacing anything
  3. Back-probe the switch signal and ground wires with a multimeter: operating the switch should change the signal state cleanly, and the ground side should drop less than 0.1 V
  4. Open the rubber boot between the door and the A-pillar and look for broken strands, which is the most common failure point on this circuit
  5. Bench-test the switch for continuity in every position and replace it only if it fails
  6. If the wiring and switch check good, confirm module supply and ground and look for a software update before condemning the module
  7. Where the code points to the occupant classification system, follow the manufacturer procedure to check OCS supply, ground and self-test, and run the zero-point calibration after any seat work

Codes From the Same System

All Fault Codes

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.