B1587 — Autolamp Delay Increase Circuit Failure #

Note: The code description may differ depending on the vehicle manufacturer (OEM). Always consult your specific vehicle’s documentation for precise terminology.

• Autolamp Delay Circuit Failure (Ford, Lincoln, Mercury)
• Automatic Headlamp Delay Malfunction (Mazda)
• Autolamp System Delay Fault (Jaguar, Land Rover)

Summary of DTC B1587 #

The B1587 Diagnostic Trouble Code (DTC) signals a malfunction in the circuit responsible for controlling the delay feature of your vehicle’s automatic headlamp system, commonly called the autolamp delay. This system is designed to keep your headlights on for a preset duration after the ignition is turned off, enhancing convenience and safety. When the control module detects an abnormality—like increased resistance, a short, or an open circuit—in this delay system, it triggers the B1587 code. Although not a “critical” code, it points to an electrical or component issue that may result in your headlamps not functioning as intended after shutdown. Addressing this code ensures your lighting system operates according to OEM design and maintains nighttime safety features.

Common Symptoms for Code B1587 #

When the B1587 code is present, you may notice subtle changes in how your vehicle’s autolamp function behaves. These symptoms often go unnoticed until you pay close attention to your headlamp’s post-ignition performance, but they can signal an underlying electrical fault that might worsen over time.

• Headlamps stay on for an unusually long (or short) period after ignition is turned off
• Autolamp system does not activate or deactivate as expected
• Warning lights or messages on the dashboard (varies by OEM)
• Manual headlamp switch required for normal operation
• Occasional flickering or delayed response of headlamps

Likely Causes for Code B1587 #

The B1587 code is most frequently triggered by issues in the electrical pathway controlling the autolamp delay. Some causes are straightforward, like a blown fuse, while others may require more in-depth troubleshooting. Here are the most common culprits, ordered by likelihood:

1. Faulty autolamp delay relay or control module
2. Damaged, corroded, or loose wiring/connectors in the autolamp circuit
3. Malfunctioning headlamp switch or sensor
4. Faulty fuse related to the autolamp system
5. Moisture or corrosion in the fuse box or connector terminals
6. Software or calibration issue in the Body Control Module (BCM)

Step-by-Step Diagnostic for B1587 #

Diagnosing the B1587 code requires a methodical approach to avoid replacing unnecessary parts. Think of it as following a detective’s trail: each step rules out common suspects and brings you closer to the real culprit.

• Verify the complaint: Check how the headlamps behave after turning off the ignition. Note any irregularities.
• Scan for additional codes: Use a professional OBD-II scanner to look for related Body or Chassis codes. Multiple codes may help pinpoint the issue.
• Inspect the fuse: Locate the autolamp or headlamp delay fuse. Check for continuity and signs of corrosion or damage.
• Examine wiring and connectors: Visually inspect the wiring harnesses and connectors from the headlamp switch to the BCM and relay. Look for frayed, pinched, or corroded wires.
• Test the autolamp relay/module: Using a multimeter, verify that the relay is receiving power and ground, and is switching correctly per OEM wiring diagrams.
• Check the headlamp switch/sensor: Test for correct operation and continuity as specified by the manufacturer’s procedures.
• Consult OEM wiring diagrams: Compare actual circuit voltages and resistances to specifications to identify abnormal readings.
• Clear the code and retest: After any repair or test, clear the code and verify the autolamp function through multiple ignition cycles.

Possible Repairs for B1587 #

Once the root cause of B1587 is identified, repairs can range from simple DIY fixes to more involved component replacements. Always match the repair to the precise issue found during diagnosis to avoid unnecessary part swaps.

• Replace a blown or faulty autolamp circuit fuse
• Repair or replace damaged/corroded wiring or connectors in the autolamp delay circuit
• Replace a faulty autolamp relay or delay control module
• Replace or recalibrate the headlamp switch or ambient light sensor if defective
• Clean and protect fuse box and connector terminals from moisture/corrosion
• Reprogram or update BCM software if indicated by OEM service bulletins

Is It Safe to Drive With Code B1587? #

Yes, you can typically continue driving with code B1587 present, but with limitations. While this code does not affect engine performance or immediate safety, it may compromise your ability to rely on the automatic headlamp feature. If the headlamps do not turn off as expected, you risk draining your battery; if they fail to illuminate in low-light conditions, visibility could be reduced. In summary: Drive with caution, use manual headlamp control, and address the code promptly to restore full safety and convenience.

Vehicles Most Commonly Affected by B1587 #

The B1587 DTC is most frequently reported in vehicles equipped with sophisticated autolamp systems, especially those manufactured by Ford and its affiliates. The code can also surface in some luxury brands that use similar headlamp control architectures.

• Ford F-Series (F-150, F-250, etc.)
• Ford Explorer, Expedition, Taurus
• Lincoln Navigator, Town Car
• Mercury Grand Marquis
• Mazda Tribute (select years)
• Jaguar S-Type, X-Type
• Land Rover LR3, Range Rover (select models)

Common Mistakes & Best Practices for B1587 #

Misdiagnosis of B1587 often stems from overlooking the basics or jumping straight to expensive module replacements. Staying systematic and respecting OEM procedures avoids wasted time and money.

• Assuming the headlamp bulbs are at fault without checking the autolamp circuit
• Ignoring wiring and connector integrity—small amounts of corrosion can cause big problems
• Replacing the relay or control module before inspecting fuses and connections
• Neglecting to clear codes and retest after repairs
• Not consulting up-to-date OEM wiring diagrams or service bulletins

FAQ Express — Code B1587 #

Here are quick answers to some common questions about B1587 — Autolamp Delay Increase Circuit Failure:

• Q: Will B1587 cause my headlamps to stay on and drain the battery?
  A: It’s possible. If the delay circuit fails in the “on” state, your headlamps may not turn off automatically. Always verify lamp operation after shutting off the ignition.
• Q: Do I need a dealer scan tool to diagnose B1587?
  A: Not always. Most OBD-II scanners can read this code, but OEM-level tools may be required for advanced diagnostics or module reprogramming.
• Q: Can weather or washing my car trigger B1587?
  A: Yes, moisture intrusion into the fuse box or connectors is a known cause. Ensure all covers and seals are intact and dry out any suspect areas before further diagnosis.