Weak, ageing or poorly charged 12 V battery that cannot support repeated restarts; Poor connections at battery terminals, starter feed or earth straps causing voltage drop during cranking; Worn starter motor, starter relay or restart-assist hardware (design varies by model and engine); Faulty battery monitoring sensor or charging system fault giving incorrect battery state information; Crankshaft or camshaft position sensor signal fault delaying engine synchronisation on restart; Fuel delivery or ignition fault that makes the engine slow to fire on a restart; Outdated control unit software where the manufacturer has published a correction for this fault.

P06EF

Engine Restart Performance.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
EF: FaultThe specific fault in that area

What it means

P06EF is the SAE J2012 generic code for Engine Restart Performance. The control unit has judged that the engine did not restart as expected after an automatic stop, for example during stop-start operation. It saw the restart take too long, run too slowly or fail compared with its expected values. The exact monitoring criteria depend on the make, model and engine.

Symptoms

Slow, delayed or extended cranking when pulling away after an automatic stop
Engine fails to restart on its own and needs the key or button to start it
Stop-start system disabled or a stop-start fault message on the dash
Engine stalls or stumbles as it restarts
Engine warning light on
Intermittent hard starting when the engine is cold or warm

Possible causes

Weak, ageing or poorly charged 12 V battery that cannot support repeated restartslikely
Poor connections at battery terminals, starter feed or earth straps causing voltage drop during crankinglikely
Worn starter motor, starter relay or restart-assist hardware (design varies by model and engine)possible
Faulty battery monitoring sensor or charging system fault giving incorrect battery state informationpossible
Crankshaft or camshaft position sensor signal fault delaying engine synchronisation on restartpossible
Fuel delivery or ignition fault that makes the engine slow to fire on a restartpossible
Outdated control unit software where the manufacturer has published a correction for this faultrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting battery voltage, engine temperature and conditions when the code set
Check for other related codes covering starter circuit, battery, charging or crank sensors and deal with those first
Inspect battery terminals, earth straps and starter wiring for corrosion, looseness or damage
Test the battery state of health and charge level, and check the charging system output
Measure voltage drop on the starter feed and earth circuits while cranking
Review live data for cranking speed, restart time and stop-start status where the vehicle supports it
Check crankshaft and camshaft sensor signals and wiring, and confirm fuel pressure and ignition operation
Check whether the manufacturer has published a software update for this fault on the vehicle

How to fix

Replace the 12 V battery if it fails testing, and make sure any battery registration the vehicle needs is carried out
Clean and tighten or repair faulty battery, earth and starter connections and damaged wiring
Repair or replace the starter motor, relay or restart-assist component if testing shows a fault
Replace a faulty battery monitoring sensor or repair the charging system
Replace a faulty crankshaft or camshaft sensor, or repair its wiring
Repair any confirmed fuel or ignition fault, and apply a manufacturer software update only if one is published for this fault

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but it may be slow to restart or stall and not restart, especially in traffic. Get it checked soon, and avoid relying on it for long journeys until the cause is found.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.