B1605

Lamp Anti-Theft Indicator Circuit Short To Battery

Body Chassis/Safety Anti-theft lamp control 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The anti-theft indicator lamp circuit is shorted directly to battery voltage, preventing the ECU from controlling it properly. Think of it like a light switch stuck in the ON position because someone bypassed the switch and connected the wire straight to the battery.

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Symptoms You May Notice

3 known symptoms for this code
Anti-theft indicator lamp stays on constantly or doesn't respond to ignition cycles
Possible battery drain if short is causing continuous current draw
No communication issues with the anti-theft system itself
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the anti-theft indicator lamp circuit voltage to verify it can pull the line low (ground) when commanded and detect proper circuit operation. A short to battery means the voltage remains high regardless of ECU commands, exceeding the expected control threshold and triggering this fault.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Lamp Circuit Voltage 0V when ON (grounded by ECU), 12V when OFF (floating) Constant 12V+ regardless of ECU command state
Circuit Control Response Voltage toggles on ECU ground signal Voltage remains high; ECU cannot control lamp state
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness and connectors
Inspect the anti-theft lamp circuit wiring for pinched, melted, or exposed insulation causing a short to the positive battery line.
2
Anti-theft indicator lamp socket/connector
Check the lamp socket for corroded or loose connections and reseat all connectors on the anti-theft module circuit.
3
Anti-theft module or body control module
If wiring tests good, the internal circuit in the control module may be shorted and require professional replacement or reprogramming.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1605 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 B1605

What happens after you fix the fault

Once the fault is repaired, B1605 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.