B1573 — Door Ajar LR Circuit Short To Battery #

Note: The label for DTC B1573 may vary depending on the manufacturer. Always refer to your OEM (Original Equipment Manufacturer) documentation for the precise terminology used for your vehicle.

• Ford: Door Ajar LR Circuit Short To Battery
• Lincoln: Door Ajar Left Rear Circuit Short To Battery
• Mercury: Rear Left Door Ajar Circuit Short To Battery

Summary of code B1573 #

The B1573 diagnostic trouble code (DTC) indicates that the vehicle’s control module has detected a short-to-battery condition in the left rear (LR) door ajar circuit. In simpler terms, this means the electrical circuit responsible for detecting whether the left rear door is open or closed is receiving an abnormally high voltage, suggesting a direct connection to battery power where there shouldn’t be one. This is often flagged by the Body Control Module (BCM), which manages the car’s interior electronics. When this code appears, common symptoms may range from false door-ajar warnings to malfunctions in interior lights. Quick action is important to avoid related electrical issues and to maintain accurate safety system operation.

Common symptoms for code B1573 #

Drivers and technicians may notice several symptoms if code B1573 is active. These issues are typically related to the door status sensors and their impact on vehicle functions like security, lighting, and alarms. Here are frequent symptoms:

• Persistent or intermittent “door ajar” warning on the dashboard
• Interior dome or courtesy lights staying on or not functioning correctly
• Remote locking/unlocking issues for the left rear door
• Alarm system false triggers (thinking the door is open when it isn’t)
• Battery drain (if lights remain on unexpectedly)

Probable causes for code B1573 #

A short to battery in the left rear door ajar circuit can stem from several possible causes. These should be checked in order of likelihood:

1. Damaged or chafed wiring in the door harness, causing a direct connection to battery voltage
2. Faulty door ajar switch (integrated into the latch assembly or as a separate component)
3. Corroded or contaminated connectors at the door or Body Control Module (BCM)
4. Water intrusion leading to short circuits within the door wiring
5. Incorrect aftermarket accessory installation (e.g., alarm, audio, or remote start systems spliced into door wiring)
6. Internal BCM malfunction (rare, but possible if all external checks are inconclusive)

Step-by-step diagnosis for code B1573 #

Diagnosing this DTC requires a methodical approach to avoid unnecessary parts replacement. Follow these steps:

1. Verify the code with a scan tool and clear it to see if it returns.
2. Visually inspect the left rear door wiring harness for signs of abrasion, pinching, or aftermarket splices.
3. Disconnect the door ajar switch and check for battery voltage on the circuit using a digital multimeter.
4. Inspect all connectors between the door and the BCM for corrosion, bent pins, or moisture.
5. Test the door ajar switch for proper open/close operation (continuity test).
6. If all wiring and switch tests pass, inspect inside the BCM for evidence of short circuits or internal failure (usually requires advanced diagnostics or OEM procedures).

Possible repairs for code B1573 #

The appropriate repair will depend on which cause is identified during diagnosis. Common fixes include:

• Repair or replace damaged wiring in the door harness
• Replace the faulty left rear door ajar switch or door latch assembly (if integrated)
• Clean and secure all connectors at the door and BCM
• Address any water leaks or sources of corrosion in the door area
• Correct or remove any improperly installed aftermarket accessories in the affected circuit
• Replace or reprogram the BCM (only if all other steps have been exhausted and OEM diagnostics confirm failure)

Is it safe to drive with code B1573? #

Limited: It is generally safe to drive with B1573, as this code doesn’t directly affect the engine or transmission operation. However, you may experience security system malfunctions, interior light issues, or even unexpected battery drain if courtesy lights stay on. If these symptoms occur, it’s best to address the issue soon to avoid getting stranded or dealing with drained battery and compromised vehicle security.

Vehicles most commonly affected by code B1573 #

This DTC is most often reported in vehicles using similar BCM and door wiring strategies—especially within the Ford family. Models frequently affected include:

• Ford F-150 and Super Duty trucks (various years)
• Ford Explorer
• Ford Expedition
• Lincoln Navigator
• Mercury Mountaineer
• Other Ford, Lincoln, and Mercury SUVs and crossovers with door ajar circuitry

Common mistakes and best practices for code B1573 #

Misdiagnosis or incomplete repairs are common with B1573 due to the complexity of modern vehicle wiring. Avoid these pitfalls and follow sound diagnostic habits:

• Assuming the door switch is always at fault without checking for wiring damage
• Overlooking connector corrosion, especially in areas prone to moisture
• Neglecting to check for aftermarket wiring add-ons that may have compromised the circuit
• Replacing the BCM prematurely without confirming all external circuits are healthy
• Always use a wiring diagram and follow OEM diagnostic procedures for your specific model

Quick FAQ for code B1573 #

Here are answers to some of the most common questions about this code:

• Q: Can I simply reset the code to fix it?
  A: Clearing the code may temporarily turn off the warning, but unless the underlying wiring or switch issue is resolved, the code will return.
• Q: Does this code mean my door is actually open?
  A: Not necessarily. The system may falsely report the door as open due to the electrical short, even if the door is physically closed.