OBD Code B1593: Autolamp Delay Decrease Circuit Short To Battery

Q: What does OBD code B1593 mean?

Autolamp Delay Decrease Circuit Short To Battery. The autolamp delay circuit is detecting too much voltage, like a wire touching the battery directly instead of being properly controlled. This causes the headlight delay function to malfunction or stay stuck on.

Q: What are the symptoms of fault code B1593?

Headlights remain on when vehicle is off, Autolamp delay feature not working, Dashboard warning light illuminated

Q: How do I fix OBD fault code B1593?

Disconnect and inspect the connector for corrosion, bent pins, or moisture, then reconnect firmly.. Visually trace the circuit harness for pinched, melted, or damaged insulation that could cause a short to battery.. Replace the module if wiring is intact, as internal failure may be causing the short condition.

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What This Actually Means

In plain language — no jargon

The autolamp delay circuit is detecting too much voltage, like a wire touching the battery directly instead of being properly controlled. This causes the headlight delay function to malfunction or stay stuck on.

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Symptoms You May Notice

3 known symptoms for this code

Headlights remain on when vehicle is off

Autolamp delay feature not working

Dashboard warning light illuminated

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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the autolamp delay circuit voltage to ensure it stays within a safe operating range. When the circuit shorts to battery voltage, the ECU detects an abnormally high voltage signal that exceeds the expected threshold, triggering the fault code.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Circuit Voltage	0.5V - 4.5V	>11V (battery short condition)
Signal Resistance	1kΩ - 10kΩ	<100Ω (short to ground or battery)

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Autolamp module harness connector

Disconnect and inspect the connector for corrosion, bent pins, or moisture, then reconnect firmly.

2

Autolamp control module wiring

Visually trace the circuit harness for pinched, melted, or damaged insulation that could cause a short to battery.

3

Autolamp delay control module

Replace the module if wiring is intact, as internal failure may be causing the short condition.

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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1593 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.

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How to Clear Code B1593

What happens after you fix the fault

Once the fault is repaired, B1593 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When

Fault has been diagnosed and repaired
You want to confirm the repair worked
Code appeared after a sensor was cleaned

⚠️ Do Not Clear When

Preparing for an emissions/PUC test
Root cause is still undiagnosed
Check engine light is flashing

Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.