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Engine-Codes – Mercury – B1691 Mercury

B1691 Mercury Code - Autolamp Delay Circuit Short To Battery

Quick Answer

The B1691 diagnostic trouble code (DTC) indicates a fault in the autolamp delay circuit, specifically a short to battery. Common causes include Damaged or frayed wiring in the autolamp delay circuit, Corroded or loose electrical connectors affecting circuit integrity, Faulty headlight switch or BCM that fails to regulate the circuit properly. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
B1691 Mercury indicates Autolamp Delay Circuit Short To Battery.
Common causes
Common causes include Damaged or frayed wiring in the autolamp delay circuit, Corroded or loose electrical connectors affecting circuit integrity, Faulty headlight switch or BCM that fails to regulate the circuit properly.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Oct 23, 2024
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Code B1691 Mercury Description

The B1691 diagnostic trouble code (DTC) indicates a fault in the autolamp delay circuit, specifically a short to battery. This code is typically associated with vehicles equipped with an automatic headlight control system that includes a delay feature for turning off the headlights after the ignition is switched off. When the system detects a short circuit in the autolamp delay circuit, it triggers this code, signaling that the circuit is receiving an unintended voltage level, which can lead to improper operation of the headlight system.

OBDII Code B1691 Mercury - Autolamp Delay Circuit Short To Battery
B1691 Mercury Code - Autolamp Delay Circuit Short To Battery

Common Causes of B1691 Mercury

  1. Damaged or frayed wiring in the autolamp delay circuit.
  2. Corroded or loose electrical connectors affecting circuit integrity.
  3. Faulty headlight switch or BCM that fails to regulate the circuit properly.
  4. Water intrusion or moisture in the electrical components, leading to short circuits.
  5. Aftermarket modifications or installations that interfere with the factory wiring.

Symptoms of B1691 Mercury

  1. Headlights remain on after the ignition is turned off.
  2. Battery drains quickly or fails to hold a charge.
  3. Malfunctioning automatic headlight feature (e.g., headlights do not turn on or off as expected).
  4. Flickering or dimming of headlights while driving.
  5. Warning lights illuminated on the dashboard related to the lighting system.

How to Fix B1691 Mercury

  1. Diagnostic Testing: Begin by using a multimeter to check for voltage in the autolamp delay circuit and identify the location of the short.
  2. Inspect Wiring and Connectors: Visually inspect the wiring harness and connectors for signs of damage, corrosion, or loose connections. Repair or replace any compromised components.
  3. Test the Headlight Switch and BCM: Use a scan tool to check for additional codes and test the functionality of the headlight switch and BCM. Replace any faulty components as necessary.
  4. Repair or Replace Damaged Components: If any wiring is found to be damaged, repair it using appropriate electrical connectors and insulation. If the BCM is faulty, it may need to be replaced and reprogrammed.
  5. Clear Codes and Test: After repairs, clear the DTCs using a scan tool and conduct a functional test of the autolamp system to ensure proper operation.

Cost to Fix B1691 Mercury

The cost to repair a B1691 code can vary significantly based on the underlying cause of the issue. Typical repair costs may range from $100 to $600. This estimate includes parts such as wiring harnesses, connectors, or switches, which can cost anywhere from $20 to $300, depending on the specific components needed. Labor costs can also vary, with most auto repair shops charging between $80 and $150 per hour. In metropolitan areas or at dealerships, rates may be higher, while independent shops may offer lower rates. Given the variability in diagnosis time and labor rates, it is advisable to check local rates for a more precise estimate tailored to your vehicle's make and model.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about B1691 Mercury Code

1. What are the common symptoms of the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery)?

- Common symptoms include malfunctioning autolamp delay circuit, interior lights staying on or not turning off, and potential draining of the vehicle's battery.

2. What could cause the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery) to trigger?

- The code can be triggered by a short circuit in the autolamp delay circuit, a faulty control module, damaged wiring, or a malfunctioning autolamp sensor.

3. How can I diagnose the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery)?

- Diagnose by inspecting the autolamp delay circuit wiring for shorts or damage, checking the autolamp sensor for proper functioning, and using a diagnostic scanner to read the code.

4. Are there any repair tips for fixing the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery)?

- Repair tips include repairing any damaged wiring in the autolamp delay circuit, replacing a faulty control module if necessary, and ensuring the autolamp sensor is working correctly.

5. Can I drive my vehicle with the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery) active?

- It is generally safe to drive the vehicle with this code, but it is recommended to address the issue promptly to avoid potential battery drain or other electrical problems.

6. How can I reset the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery) after making repairs?

- Use a diagnostic scanner to clear the code after repairing the autolamp delay circuit short to battery issue. Alternatively, the code may reset automatically after a certain number of driving cycles.

7. Is it possible for the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery) to return after being cleared?

- If the underlying issue causing the code is not properly addressed, it is possible for the code to return. Ensure all repairs have been completed correctly to prevent this.

8. Can a DIY enthusiast fix the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery)?

- Depending on your skill level and access to tools, DIY enthusiasts may be able to diagnose and repair this code by following repair guides and using the necessary equipment.

9. What is the typical cost of repairing the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery) at a mechanic or dealership?

- The cost of repair can vary depending on the exact cause of the issue, but it may involve labor charges for diagnosis and repair, as well as the cost of any replacement parts needed.

10. Are there any recalls or service bulletins related to the OBDII code B1691 Mercury (Autolamp Delay Circuit Short To Battery)?

- Checking with the manufacturer or authorized dealerships for any recalls or service bulletins related to this specific OBDII code is recommended to stay informed about potential known issues and solutions.

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