OBD Code B1550: Door Lock Motor Circuit Malfunction – Causes, Symptoms & Fixes

Code B1550 is a body system diagnostic trouble code that points to a problem with your vehicle’s door lock motor circuit. This code means your vehicle’s onboard diagnostic system has detected an electrical fault in the power door lock system—specifically in the motor that physically locks and unlocks your doors. While this isn’t a critical engine code, it can affect your vehicle’s security and convenience features.

What Does B1550 Mean?

B1550 is a generic OBD-II body code that indicates a malfunction in the door lock motor circuit. The “B” prefix tells you this is a body system code (as opposed to powertrain or chassis codes). The door lock motor is an electric motor responsible for mechanically engaging and disengaging your vehicle’s door locks when you press the power lock button or use your key fob.

When this code is triggered, it means the vehicle’s body control module (BCM) has detected one or more of the following:

• An open circuit (broken wire or connection)
• A short circuit (wires touching or damaged insulation)
• A motor that isn’t responding to commands
• Excessive current draw from the motor
• A faulty motor relay or control circuit

Common Symptoms

Drivers experiencing code B1550 typically notice one or more of these warning signs:

• Power locks not working: One or more doors won’t lock or unlock when you press the button
• Intermittent locking: Doors lock and unlock sporadically or only work sometimes
• Slow lock response: The locks take longer than normal to engage
• Check Engine or Body System light: The dashboard warning light illuminates
• Key fob not working: Remote locking/unlocking fails while manual locks still work
• Clicking sounds from door: You hear the motor trying to engage but failing
• One door affected: Only one door’s lock motor malfunctions while others work fine

Possible Causes

B1550 can stem from several issues, ranked from most to least common:

1. Faulty Door Lock Motor (Most Common)

The motor itself has failed internally due to wear, age, or manufacturing defect. This is the most frequent cause, especially in vehicles over 10 years old. The motor’s brushes wear out, windings short, or mechanical components seize.

2. Corroded or Loose Electrical Connectors

The connector plugging the motor into the vehicle’s wiring harness has corroded, loosened, or become partially disconnected. This is especially common in vehicles exposed to salt, moisture, or extreme weather.

3. Broken or Damaged Wiring

The wiring harness leading to the door lock motor is damaged, pinched, or corroded. This can happen from door slamming, rodent damage, or age-related deterioration.

4. Faulty Door Lock Relay

The relay controlling power to the door lock motors has failed. This component switches power on and off to the motors based on BCM commands.

5. Body Control Module (BCM) Malfunction

The BCM itself is faulty and incorrectly reporting a motor problem or failing to send proper signals. This is less common but possible.

6. Low Battery Voltage

Insufficient electrical power prevents the motor from operating correctly. A weak battery or charging system problem can trigger this code.

7. Blown Fuse

The fuse protecting the door lock circuit has blown, cutting power to the system.

Diagnostic Steps

Follow these steps to diagnose code B1550:

Step 1: Retrieve and Clear the Code

Use an OBD-II scanner to confirm code B1550 and check for any additional codes. Write down all codes present. Clear the code and test-drive to see if it returns immediately (indicating an active fault) or if it was intermittent.

Step 2: Inspect the Battery and Charging System

Check your battery voltage with a multimeter—it should read 12.6V when the engine is off and 13.5-14.5V when running. If voltage is low, charge or replace the battery before proceeding.

Step 3: Check the Door Lock Fuse

Locate your vehicle’s fuse panel (consult your owner’s manual for location). Find the door lock fuse and inspect it for a broken filament. Replace if necessary. The fuse is typically 15-20 amps.

Step 4: Test the Door Lock Switches and Buttons

Try operating the power lock button from the driver’s door panel. If it works, the problem is likely isolated to one specific door’s motor. If nothing works, the problem is likely upstream (relay, fuse, or wiring).

Step 5: Inspect Door Lock Motor Connectors

Open the door panel and locate the door lock motor connector. Look for corrosion, loose pins, or water damage. Gently disconnect and reconnect the connector several times to ensure good contact. If corroded, clean with electrical contact cleaner.

Step 6: Test Motor Continuity

Disconnect the door lock motor completely. Using a multimeter set to resistance (ohms), test the motor’s continuity. A functioning motor should show some resistance (typically 5-15 ohms depending on the motor). If you read infinite resistance or zero ohms, the motor is faulty.

Step 7: Check Wiring Harness

Inspect the wiring harness leading to the door lock motor for visible damage, pinching, or corrosion. Look for exposed wires or melted insulation. Trace the wires from the motor back to the main harness.

Step 8: Test the Door Lock Relay

Locate the door lock relay in the fuse/relay panel. Swap it with an identical relay (if available) to test. Some relays can be tested with a multimeter by checking for continuity when voltage is applied to the coil.

Step 9: Perform a Door Lock Motor Replacement Test

If all other components test fine, the motor itself is likely faulty. Replace the door lock motor and retest. This is often the most straightforward solution.

Repair Cost Estimates

The cost to repair code B1550 varies depending on the root cause:

• Door Lock Motor Replacement: $150–$400 per motor (parts + labor). Most vehicles have one motor per door, so multiple failures increase cost.
• Connector Repair/Replacement: $50–$150 if corrosion cleaning or connector replacement is needed.
• Wiring Harness Repair: $100–$300 depending on the extent of damage and labor time.
• Door Lock Relay Replacement: $30–$100 for the relay itself; labor is minimal.
• Fuse Replacement: $10–$30, often a DIY fix.
• BCM Reprogramming/Replacement: $300–$1,000+ if the body control module is at fault (rare).

Typical Total Repair Cost: $200–$500 for a single door lock motor replacement, which is the most common fix.

Can I Still Drive?

Code B1550 is not a critical safety issue and won’t prevent your vehicle from starting or running. However, you should address it for these reasons:

• Security Risk: If your locks don’t work, your vehicle is less secure. Thieves may target a car with non-functional locks.
• Convenience: You may be unable to lock or unlock your doors remotely, forcing you to use manual locks.
• Resale Value: A persistent body code can lower your vehicle’s trade-in or resale value.
• Warranty: If your vehicle is under warranty, this issue should be covered—get it repaired at the dealership.

You can safely drive with this code present, but schedule a repair within a few weeks to restore full functionality and security.

Frequently Asked Questions