B1508

Flash To Pass Switch Circuit Open

Body Chassis/Safety Lighting Control 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The flash-to-pass switch circuit is broken or disconnected, preventing the headlight high-beam flash feature from working. Think of it like a light switch with a loose wire—the signal can't complete its path to the module.

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Symptoms You May Notice

3 known symptoms for this code
Flash-to-pass headlight feature does not function
High beam flashing inoperative when pulling turn signal stalk
No response from headlight module to flash command
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The body control module monitors the flash-to-pass switch circuit for a voltage signal when the driver activates the high-beam momentary flash. The ECU expects a valid voltage transition when the switch closes; an open circuit means no signal reaches the module, triggering a fault.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Switch Circuit Voltage 0V (open) to 12V (closed) No voltage transition detected; circuit remains open
Signal Recognition Time Signal detected within 500ms of switch activation No signal detected; open circuit condition
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness connector at steering column
Inspect and reseat the connector supplying power to the flash-to-pass switch circuit.
2
Flash-to-pass switch assembly
Test switch continuity with a multimeter; replace if no continuity is detected when activated.
3
Wiring between switch and body control module
Check for damaged insulation, corrosion, or broken wire strands along the entire circuit path.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1508 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 B1508

What happens after you fix the fault

Once the fault is repaired, B1508 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.