P06EF: Engine Restart Performance
What to do
If the battery has been replaced, ask two questions: was it the correct type, and was it registered to the car? Stop-start vehicles need a specific battery — AGM or EFB, not an ordinary one — and most need it coded to the module afterwards. A cheaper battery, or one fitted without registering, causes exactly this fault and wears out quickly.
Expect stop-start to switch itself off. That is the system protecting you from a slow restart at a junction, not an additional fault.
Have the battery load tested rather than voltage tested, since a battery can read fine and still fail under load.
Mention when the oil was last changed and what grade, since thick or degraded oil makes restarts slower.
What this code means
The engine is not restarting the way the stop-start system requires.
A stop-start restart is a different event from a cold start, and this code exists because the standard is much higher. The driver is at a junction with their foot on the brake, expecting the car to move the instant they release it. A restart that takes an extra second is not merely slow — it is the reason people switch the system off.
So the module holds restarts to a tight standard, measuring how fast the engine reaches idle and how smoothly it gets there. This code says it fell short.
The battery deserves first attention, and stop-start batteries are not ordinary batteries. These vehicles use AGM or EFB types built for many shallow discharges. Fitting a conventional battery is a common and expensive shortcut — it works briefly, ages rapidly under stop-start duty, and produces exactly this fault.
Registration matters as much as the battery itself. Most of these vehicles need a replacement battery coded to the module, and one fitted without that step is charged to the wrong profile and degrades early. Ask whether it was done.
Beyond the battery, look at what makes a restart hard: a starter that is worn from heavy use, thick or degraded oil, or a fuel system slow to build pressure after a stop.
Expect the system to disable itself rather than keep trying, which is correct behaviour and not a second fault.
Likely causes
Start here
- New battery not registered to the vehicle · specialist
- Incorrect battery type fitted for stop-start · easy
- Low system voltage · easy
Less common
- Worn starter motor · moderate
- Incorrect oil grade or degraded oil · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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