P06EF: Engine Restart Performance

What it means

After a stop-start auto-stop the engine takes longer than calibrated to restart, or restart is missed. Possible causes are weak starter, low battery state of charge, weak crank position signal at low RPM, or a fuel rail that lost prime.

At a glance

• Usually lights the check-engine light

How it works

The stop-start system shuts the engine off temporarily and monitors how promptly it restarts when the driver is ready to move. P06EF sets when a restart after an automatic stop takes longer than the system expects or does not complete, with possible causes including battery, starter, crank-signal, fuel-pressure, or control faults.

Common causes

Most likely first.

1. Weak or discharged battery
2. Worn starter or stop-start starter circuit fault
3. Crankshaft position signal problem during restart
4. Fuel pressure or priming problem
5. Stop-start system control fault

Symptoms

• Check engine light on
• Possible limp mode or no-start
• Multiple follow-up faults across modules
• Reset/relearn may be needed after repair

How to diagnose it

1. Record freeze-frame data and scan the engine, battery, and stop-start systems for restart, charging, crank-signal, or fuel-pressure faults.
2. Check battery state of charge and condition, and inspect battery terminals and grounds because stop-start restarts place repeated demands on the electrical system.
3. Review restart speed and crankshaft-position signal data during an automatic restart, comparing them with the manufacturer's diagnostic information.
4. Inspect the stop-start starter and its control wiring for loose connections, heat damage, or corrosion, then test the circuit according to the wiring diagram.
5. If the electrical and crank-signal checks pass, check fuel pressure or priming behaviour during restart using the manufacturer's procedure.
6. If those checks pass, diagnose the stop-start control system using the recorded conditions and manufacturer information.

Common fixes

• Charge or replace a weak battery after confirming its condition and charging system operation.
• Clean or repair battery, ground, starter, or stop-start control connections that fail inspection.
• Repair a crankshaft-position sensor circuit fault confirmed during restart testing.
• Repair a fuel-pressure or priming fault confirmed during restart testing.
• Replace a starter or repair the stop-start control system only if its specified tests identify the fault.

Can I keep driving?

The engine may not restart after an automatic stop, so disable stop-start if the vehicle provides that option until the cause is diagnosed. Avoid relying on automatic restarts in traffic; if the engine stalls and will not restart, move to a safe location and request assistance.