B1593 — Autolamp Delay Decrease Circuit Short To Battery #

Note: The code description may vary depending on the vehicle manufacturer.

• Autolamp Delay Decrease Circuit Short To Battery (Ford, Lincoln, Mercury)
• Autolamp Timer Decrease Input Circuit Shorted High (Mazda)
• Autolamp Delay Reduce Input Circuit Short to Voltage (General variation)

Summary of DTC B1593 #

DTC B1593 is a diagnostic trouble code that points to an issue within the autolamp delay decrease circuit — specifically, a short to battery voltage. The autolamp system is responsible for automatically turning the vehicle’s exterior lights on or off based on ambient light conditions, with a customizable delay after the ignition is turned off. When this code sets, it means the system detects voltage where it expects a decrease signal, often indicating an electrical fault. While primarily a comfort and convenience feature, this malfunction can sometimes impact nighttime safety if lights don’t operate as intended. Addressing this code promptly ensures your autolamps function reliably and as designed.

Common Symptoms for Code B1593 #

When B1593 is present, you may notice changes in how your autolamp system behaves. Although some drivers might overlook minor quirks, these symptoms can affect your night driving experience and vehicle confidence. Typical signs include:

• Headlights remain on longer than set delay or fail to turn off automatically
• Autolamp delay adjustment does not respond or behaves erratically
• Warning lights or messages on the dashboard (e.g., “Auto Headlamp Fault”)
• Possible battery drain if lights stay on unexpectedly
• Manual override required to turn off exterior lights

Most Likely Causes for DTC B1593 #

B1593 is most frequently triggered by electrical faults in the autolamp system’s delay decrease circuit. Understanding what typically causes this helps prioritize your diagnostic approach. The most common origins, in order of likelihood, are:

1. Short to battery voltage in the autolamp delay decrease circuit (damaged wiring or connector pinched to live power)
2. Faulty autolamp switch (internal short or contamination)
3. Defective Body Control Module (BCM) or Smart Junction Box (SJB), which manages the autolamp logic
4. Incorrect installation of aftermarket accessories (alarm, remote start interfering with the circuit)
5. Corrosion or water intrusion at connectors in the headlamp/autolamp harness

Step-by-Step Diagnostic for Code B1593 #

Diagnosing B1593 can be straightforward with methodical checks. Treat the process like following a map—each step brings you closer to the source of the issue. Here’s a structured approach:

• Verify the code with a professional-grade OBD-II/EOBD scanner, and note freeze-frame data for conditions when the code set.
• Inspect the autolamp switch and related connectors for signs of damage, corrosion, or contamination.
• Check the delay decrease circuit wiring (consult OEM wiring diagram) for pinched, frayed, or melted wires, especially where the harness passes through sharp body panels.
• Test for presence of battery voltage at the circuit (should only be present when commanded by the system). Use a multimeter to confirm.
• Disconnect the Body Control Module (BCM) or Smart Junction Box (SJB) and retest the circuit for a short to battery. If voltage persists, the short is in the wiring, not the module.
• If all wiring and switch checks pass, suspect a faulty BCM/SJB (internal short).

Possible Repairs for B1593 #

Once the source is identified, repair strategies should directly address the underlying cause. Most repairs are electrical in nature, but component replacement may be necessary. Consider the following solutions:

• Repair or replace damaged wiring and connectors in the autolamp delay decrease circuit.
• Clean or replace the autolamp switch if it’s internally shorted or contaminated.
• Correct any improper aftermarket accessory wiring interfering with the autolamp circuits.
• Repair connector corrosion or water intrusion with appropriate cleaning and dielectric grease.
• Replace the BCM or SJB only if diagnostics confirm an internal defect after all wiring checks.

Is It Safe to Drive with Code B1593? #

Limited — Caution Advised: You can usually drive with B1593 present, but there are caveats. If your headlights stay on after parking, you risk a dead battery. If the autolamps don’t function at night or in tunnels, your visibility and safety could be compromised. Manual operation is generally possible, but address the code promptly to avoid inconvenience or battery issues.

Vehicles Most Commonly Affected by B1593 #

B1593 is most frequently seen in vehicles from manufacturers that use autolamp delay systems. While primarily associated with Ford and its related brands, other OEMs with similar features may also log this code (under similar descriptions). Models most often affected include:

• Ford F-150, F-250, Expedition, Explorer, Escape
• Lincoln Navigator, MKX, Town Car
• Mercury Mountaineer, Grand Marquis
• Mazda Tribute (shared platforms)

Common Mistakes & Best Practices for Code B1593 #

Avoiding wasted time and repeat repairs is all about smart troubleshooting. Here are the usual pitfalls and how to sidestep them:

• Not checking for aftermarket accessories interfering with OEM wiring.
• Overlooking signs of moisture or corrosion in connectors near the firewall or kick panels.
• Assuming the BCM or SJB is faulty before confirming wiring integrity.
• Clearing the code without performing a root cause analysis—issue will return!
• Skipping the use of OEM wiring diagrams for accurate circuit tracing.

Quick FAQ for B1593 #

Still have questions? Here are quick answers to common concerns:

• Q: Will B1593 cause my headlights to fail completely?
  A: Not always. The manual headlight function often remains, but automatic control and delay features may be unreliable or inoperable.
• Q: Can I bypass the autolamp system to avoid this code?
  A: Bypassing isn’t recommended. It may create additional electrical issues or safety concerns, and can complicate future diagnostics or repairs.