B1572 — Door Ajar LR Circuit Open #

Note: The description for code B1572 may vary depending on the vehicle manufacturer (OEM). Always refer to your specific service manual for details.

• Door Ajar LR Circuit Open (Ford, Lincoln, Mercury)
• Left Rear Door Ajar Switch Circuit Open (GM, Chevrolet, Cadillac)
• Left Rear Door Open Circuit (Chrysler, Dodge, Jeep)

Summary of code B1572 #

B1572 indicates that the vehicle’s control module has detected an “open circuit” in the Left Rear (LR) door ajar switch circuit. In plain English, the system believes the left rear door is not properly closed, or the electrical signal confirming its closed position is lost. This detection can stem from a faulty door switch, a wiring problem, or a malfunction within the control unit itself. The code is triggered when the expected feedback from the LR door ajar sensor is absent or outside of normal parameters. Depending on the vehicle, this may cause warning lights, chimes, or issues with automatic locking features.

Common symptoms for B1572 #

When B1572 appears, you’ll likely notice some annoyances or even security risks. The most frequent symptoms include warning messages or lights, and sometimes behaviors like lights staying on when they shouldn’t. Here’s what to watch for:

• “Door Ajar” warning light or message (even when all doors are closed)
• Dome/interior lights staying on after the vehicle is locked or in motion
• Power locks not engaging automatically when driving
• Audible chimes indicating a door is open
• Battery drain if lights remain on for extended periods
• Vehicle alarm issues (false alarms or failure to arm)

Most likely causes for B1572 (ranked) #

B1572 usually arises from electrical faults related to the door ajar switch circuit for the left rear door. Here are the most common culprits, listed from most to least frequent:

1. Faulty left rear door ajar switch (the sensor inside the door latch that detects open/closed position)
2. Broken or damaged wiring to the LR door switch (often in the flexible rubber boot between the door and the body)
3. Poor or corroded connectors at the switch or in the wiring harness
4. Malfunction in the vehicle’s Body Control Module (BCM) (the computer handling door signals)
5. Physical misalignment of the door latch causing improper switch operation

Step-by-step diagnosis for B1572 #

Diagnosing B1572 doesn’t require advanced tools, but following a methodical process can save time and frustration. Here’s how a technician would typically approach it:

• 1. Confirm the code and symptoms using a scan tool. Clear the code and see if it returns immediately.
• 2. Inspect the left rear door physically: Open and close the door firmly. Check for any obvious misalignment or visible damage.
• 3. Test the door ajar switch: Observe if the dome light or “door open” warning changes as you move the latch manually with the door open.
• 4. Check wiring and connectors: Gently pull back the rubber boot between the door and body to inspect for broken, pinched, or corroded wires and connectors.
• 5. Test switch output: Use a multimeter to check for continuity at the switch terminals as you move the latch mechanism.
• 6. Inspect the Body Control Module (BCM): If all else checks out, consult OEM wiring diagrams and test BCM input/output for the LR door circuit.
• 7. Repair faults as needed, clear codes, and retest the system.

Possible repairs for B1572 #

Once the underlying cause is identified, repairs for B1572 are typically straightforward. Here’s what’s commonly done:

• Replace the left rear door ajar switch (often integrated into the door latch mechanism)
• Repair or replace damaged wiring in the door harness or rubber boot area
• Clean or replace corroded connectors at the switch or harness
• Adjust or align the door latch to ensure proper switch activation
• In rare cases, replace or reprogram the Body Control Module (BCM) if it’s not reading the switch input correctly

Is it safe to drive with code B1572? #

Yes, you can usually drive with code B1572 present, but with limitations. This code won’t cause engine or transmission issues, but it can disable or confuse important features like automatic locking, interior lights, or security systems. If the dome lights stay on, there’s a risk of battery drain if the vehicle is left parked for a long time. Address the issue soon to avoid being stranded with a dead battery or dealing with false alarms.

Vehicles most commonly affected by B1572 #

B1572 is most often reported on vehicles from manufacturers who use this code for door circuits. You’re more likely to see it in:

• Ford (Explorer, Expedition, Focus, Taurus, Fusion, F-150, Edge, Escape)
• Lincoln (MKX, Navigator, MKZ)
• Mercury (Mountaineer, Milan)
• Some GM brands (Chevrolet Malibu, Cadillac CTS, GMC Acadia)
• Chrysler, Dodge, Jeep in select models with advanced door monitoring

Always check your specific service documentation, as OEMs may use different codes or circuit designs.

Common mistakes & best practices for B1572 #

Experienced technicians know that chasing door circuit faults can be tricky. Here’s what often goes wrong — and how to do it right:

• Mistaking a physical latch problem for a wiring fault (Always check door alignment and latch movement first)
• Overlooking broken wires in the door harness boot (This is a notorious trouble spot due to constant flexing)
• Replacing the switch or latch without testing wiring continuity
• Ignoring corroded connectors (Moisture intrusion is common in door circuits)
• Not resetting the code after repairs (Always clear the code and confirm it does not return)

Express FAQ for B1572 #

Here are quick answers to the most common questions about this trouble code:

• Q: Will my car fail inspection because of B1572?
  A: Usually not, as this is not an emissions-related code. However, some states may flag any warning lights as a reason to fail.
• Q: Can I bypass the door ajar switch to clear the warning?
  A: Technically possible, but not recommended. Bypassing the switch can disable safety features and may create new electrical problems. Proper repair is always better.