B1571 Door Ajar LR Circuit Failure

Introduction:

The B1571 trouble code indicates a problem within the door ajar circuit, specifically on the left rear (LR) door. This code signals that the vehicle's computer, typically the body control module (BCM), is detecting an issue with the electrical circuit that monitors whether the left rear door is properly closed. This can lead to annoying symptoms like the interior lights staying on, the door ajar warning light illuminating, and the vehicle's security system malfunctioning.

Table: B1571 Door Ajar LR Circuit Failure Details

Detailed Explanations

Definition: Door Ajar Circuit Failure (Left Rear)

The B1571 code is a diagnostic trouble code (DTC) that is triggered when the vehicle's computer detects an issue within the electrical circuit responsible for monitoring the status of the left rear door. This circuit typically includes a door ajar switch, wiring, connectors, and the body control module (BCM). The code specifically indicates that the BCM is receiving an unexpected signal or no signal from the door ajar switch, suggesting a problem in the circuit’s ability to accurately detect whether the door is open or closed.

Symptoms

• Door ajar warning light illuminated: This is the most common and obvious symptom. The light will stay on even when the door is supposedly closed.
• Interior lights staying on: The interior lights are often tied to the door ajar circuit. If the system thinks the door is open, the lights will remain illuminated, potentially draining the battery.
• Security system malfunctioning: The vehicle's security system may not arm properly if it detects an open door, leading to false alarms or the inability to lock the car remotely.
• Battery drain: A constant drain on the battery can occur if the interior lights are continuously on due to the faulty door ajar signal.
• Door not locking properly: In some cases, the vehicle may prevent the door from locking electronically if it believes the door is ajar.
• Inability to remote start: Many vehicles disable remote start if a door is detected as open, as a safety precaution.
• Erratic operation of power windows/locks (rare): While less common, electrical interference from the faulty circuit could potentially affect other door-related functions.
• Dome light flickering: An intermittent connection can cause the dome light to flicker.

Potential Causes

• Faulty door ajar switch (LR): The door ajar switch is a simple component that closes or opens a circuit when the door is opened or closed. This switch is often located in the door jamb. A failing switch is the most common culprit.
• Wiring harness issues (damaged, shorted, open): The wiring that connects the door ajar switch to the BCM can become damaged due to wear and tear, chafing, or rodent activity. This can result in a short circuit (connection to ground or voltage), an open circuit (broken wire), or increased resistance.
• Corroded connectors: Corrosion on the electrical connectors can impede the flow of electricity, leading to a false signal or no signal at all.
• Faulty Body Control Module (BCM): While less common, the BCM itself could be the source of the problem. Internal failures within the BCM can cause it to misinterpret the signals from the door ajar switch.
• Water intrusion: Water entering the door or the vehicle's interior can cause corrosion and short circuits within the wiring and connectors.
• Incorrect door alignment: If the door is not properly aligned, it may not fully depress the door ajar switch, leading to a false signal.
• Aftermarket alarm system interference: Aftermarket alarm systems can sometimes interfere with the vehicle's electrical system, causing false door ajar signals.
• High resistance in the circuit: Corrosion, loose connections, or damaged wiring can increase the resistance in the circuit, affecting the signal strength.
• Low voltage in the circuit: A weak or failing battery, or a problem with the vehicle's charging system, can result in low voltage in the circuit, causing the door ajar switch to malfunction.
• Short to ground: A wire making unintended contact with the vehicle's chassis (ground) can create a short circuit.
• Short to voltage: A wire making unintended contact with a voltage source (e.g., another wire) can create a short circuit.
• Loose connections: Loose or improperly secured electrical connectors can cause intermittent problems.
• Damaged door jamb: Physical damage to the door jamb can affect the operation of the door ajar switch.
• Previous accident damage: Past accidents can damage the wiring or the door ajar switch, leading to problems.
• Incorrect installation of door components: If door components were not installed correctly during a repair or modification, it could cause the door ajar switch to malfunction.
• Foreign object obstructing door closure: An object preventing the door from fully closing can trigger the sensor.

Diagnostic Steps

1. Scan for codes: Use an OBD-II scanner to confirm the presence of the B1571 code and check for any other related codes.
2. Visually inspect wiring and connectors: Carefully examine the wiring harness and connectors associated with the left rear door ajar switch. Look for signs of damage, corrosion, or loose connections. Pay close attention to areas where the wiring passes through the door jamb.
3. Test door ajar switch continuity: Use a multimeter to test the continuity of the door ajar switch. The switch should show continuity when the door is open and no continuity when the door is closed.
4. Check wiring diagrams: Consult the vehicle's wiring diagrams to understand the circuit layout and identify the correct wires to test.
5. Measure voltage and resistance in the circuit: Use a multimeter to measure the voltage and resistance in the circuit. This can help identify shorts, open circuits, or high resistance.
6. Inspect door alignment: Check the door alignment to ensure that it is closing properly and fully depressing the door ajar switch.
7. Check for water intrusion: Look for signs of water damage in the door and the surrounding area.
8. Verify BCM functionality: If all other possibilities have been ruled out, the BCM may need to be tested by a qualified technician.
9. Inspect door jamb for damage: Examine the door jamb for any signs of damage that could be affecting the operation of the door ajar switch.
10. Review recent repairs or modifications: Consider any recent repairs or modifications that may have affected the door ajar circuit.

Frequently Asked Questions

What does the B1571 code mean?

The B1571 code indicates a problem with the door ajar circuit on the left rear door, meaning the system isn't correctly registering the door's open/closed state.

Can I drive my car with a B1571 code?

Yes, you can generally drive your car, but you might experience issues like a constantly lit door ajar light, interior lights staying on, and potential battery drain.

What is the most common cause of the B1571 code?

The most common cause is a faulty door ajar switch on the left rear door.

How do I fix the B1571 code?

Fixing the code involves diagnosing the problem (switch, wiring, BCM) and then repairing or replacing the faulty component.

Can I fix the B1571 code myself?

If you have basic automotive repair skills and tools (multimeter, wiring diagrams), you might be able to diagnose and fix the problem. Otherwise, professional help is recommended.

Conclusion

The B1571 code represents a malfunction in the door ajar circuit of the left rear door, frequently stemming from a faulty switch or wiring issues. Thorough diagnosis and repair are essential to restore proper functionality and prevent related problems like battery drain and security system malfunctions.