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DTC codes / P06xx · Computer and output circuits / P06F4

P06F4Stop-Start Mode Lamp Control Circuit

P06F4 indicates that the engine control module has detected a fault in the control circuit for the stop-start mode lamp, which is the indicator that tells the driver when the automatic engine stop-start feature is active, unavailable, or disabled. The computer monitors the circuit for expected voltage or current and sets this code when the signal is outside the normal range, often due to an open, short, or component failure.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • The stop-start mode lamp may not illuminate at all when the system is active or when the driver presses the disable button.
  • The lamp may stay illuminated continuously regardless of stop-start system status.
  • The stop-start system may be disabled entirely, with no indication to the driver.
  • A warning light or message on the dashboard related to stop-start system malfunction.
  • Often no symptoms besides the warning light, especially if the lamp failure is not immediately noticeable.
  • Other stop-start related functions may be inoperative, such as the engine not shutting off at stops.

Common causes, most likely first

  1. Failed stop-start mode lamp bulb or LED assembly.
  2. Open or short circuit in the wiring between the control module and the lamp.
  3. Corroded or loose electrical connector at the lamp or control module.
  4. Faulty stop-start mode switch or button that incorporates the lamp.
  5. Internal failure in the body control module or engine control module driver for the lamp circuit.
  6. Blown fuse or relay supplying power to the lamp circuit (if applicable).

How to diagnose and fix it

  1. Verify the condition of the stop-start mode lamp by visual inspection and check if it illuminates during bulb test or when activating the system.
  2. Check all fuses and relays related to the stop-start system and lamp circuit, replacing any that are blown or faulty.
  3. Inspect the wiring harness and connectors at the lamp, switch, and control modules for damage, corrosion, or loose pins; repair as needed.
  4. Test the lamp circuit with a multimeter to check for power, ground, and continuity, following the manufacturer's wiring diagram.
  5. If the lamp is a separate serviceable unit, swap it with a known-good lamp to confirm the fault.
  6. Check for technical service bulletins or software updates for the control module that may address lamp circuit faults.
  7. If all external components test good, diagnose the control module by checking its outputs and consider replacement or reprogramming if faulty.

Stop-Start Lamp Circuit Quirks and Checks

  • A failed stop-start mode lamp often goes unnoticed because the system may still function, but the code will disable the stop-start feature entirely to avoid driver confusion.
  • Some vehicles use the same lamp to indicate multiple stop-start states, so a fault may cause the lamp to flash or display incorrect colors rather than simply staying off.
  • The stop-start mode lamp circuit is sometimes integrated into the instrument cluster, meaning a cluster fault can set this code even if the lamp itself is good.
  • Aftermarket accessories or improper electrical repairs tapping into the stop-start circuit can introduce resistance or shorts that trigger P06F4.
  • A weak or failing battery can cause voltage drops that affect the lamp circuit, leading to this code even when the lamp and wiring are intact.

Can I keep driving with P06F4?

The vehicle remains safe to drive because the stop-start lamp is an informational indicator and does not affect engine operation or safety systems. However, the stop-start feature may be disabled, so you should not rely on it until the fault is repaired.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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