Start Stop Off disables the automatic engine stop in the ECU software. The engine no longer shuts down at traffic lights and in queues, and the driver no longer has to switch the system off with the button after every start. For tuners: send us the original file and get a ready-to-flash file with corrected checksums, on average in 30–60 minutes.
When the ECU stops the engine by itself
Start-stop only kicks in when a long list of conditions is met at the same time. The engine ECU checks some of them with its own sensors and gets the rest from other modules. This is how a 2019 Audi service bulletin lists them:
- the engine is warm and running below 1,200 rpm;
- since the ignition was switched on, the car has already driven faster than 10 km/h (3 km/h with a manual gearbox);
- the battery holds enough charge for a restart, which the battery manager monitors constantly;
- the driver's seat belt is fastened, the driver's door and the bonnet are closed;
- windscreen defrost is off and the climate control has reached the set temperature;
- the incline is under 10° and the steering wheel is turned no more than 270°;
- the diesel particulate filter is not regenerating;
- with an automatic the brake pedal is held, with a manual the gearbox is in neutral and the clutch is released.
The engine restarts when the driver releases the brake or presses the clutch. The ECU also restarts it on its own if the car rolls faster than 3 km/h, brake servo vacuum drops, battery charge falls, defrost is switched on or the cabin temperature drifts away from the setting.
Why people switch start-stop off
Mostly for comfort. In a slow queue the engine stops and restarts again and again, and many drivers find that irritating. There are technical reasons too:
- Number of starts. Federal-Mogul estimates that a car without start-stop makes about 50,000 starts in its life, and one with start-stop up to 500,000. These cars get reinforced starters (Bosch rates its start-stop starters for up to 3.5 times the cycles of a conventional one) and crankshaft bearings with a polymer coating. The parts are built for it, but every start still uses up starter life.
- Battery. The system needs an AGM or EFB battery designed for frequent discharge and charge cycles. It costs more than a conventional one, and after replacement it has to be adapted to the car.
- Turbo after hard driving. Kia, for example, tells owners in its manuals to let a turbocharged engine idle for about a minute after high-speed or heavy-load driving. An automatic stop right after leaving the motorway or after towing works against that. Renault and Ford hold patents on logic that delays the automatic stop while the exhaust gas ahead of the turbine or the oil is hot. Whether a given car has such protection cannot be checked from public data.
Engines with start-stop are designed for frequent starts from the outset, so the system by itself does not ruin the engine. People turn it off for comfort and to spare the starter and the battery.
When start-stop stops working
There is also the opposite complaint: the system no longer stops the engine when it should. Usually the battery is to blame. A Volkswagen technical tip says the function is blocked when the gateway (J533) sees battery charge below 12.1 V, even if every other condition is met. Short trips and high-current consumers are typical causes.
After replacing the battery or its monitoring module (J367), both have to be adapted to the car, otherwise charging suffers and the new battery may fail early. Audi notes that even after adaptation the system needs about 10 start cycles to calculate the charging curve and stays off until then. Start-stop also stays off while any related module has faults stored. If the customer wants the system back, start with the battery and the fault memory.
Ways to switch it off: button, coding, module or ECU file
| Method | How it works | Limitations |
|---|---|---|
| Button in the cabin | Switches the system off until the next start | On VW the function comes back on every time the ignition is switched on |
| Coding, adaptations | Turns the function off or changes thresholds, for example battery voltage | Not available on every car; dashboard messages may appear, on VW "Error: start–stop" |
| Module behind the button | Remembers the last button position or inverts its logic | Extra electronics in the cabin wiring |
| ECU file | The automatic stop is disabled in the software itself | The ECU has to be read and written; on some cars the engine ECU is not the only module that decides |
What changes in the software
The decision to stop the engine is made by the ECU software, and the calibration holds the parameters that allow it. The Start Stop Off file blocks the automatic stop: the conditions at a traffic light may all be met, but the ECU will not issue the stop command. No automatic stop means no automatic restart either.
Goes away
- automatic stop at lights and in traffic
- the starter restart that follows it
- switching the system off with the button after every start
Stays as before
- normal starting with the key or the Start button
- the rest of the engine calibration
- battery requirements and battery adaptation
Checksums are recalculated, so the file is ready to flash straight away. Stage 1 or DTC Off for individual fault codes can go into the same order. Supported ECUs are listed below; if yours is missing, send the file with a request.
What to check in the workshop
- Before flashing, read faults in all modules and check the battery: if the customer complains about start-stop, the battery may be the cause.
- Battery. Charging is still run by the car's energy management, which is set up for the battery type fitted at the factory. VARTA puts it plainly: a car with an AGM battery needs an AGM battery. A new battery still has to be adapted to the car, as before.
- After flashing, warm the engine up and stop with every condition met: belt fastened, doors closed, brake pressed. The engine should keep running.
- Recent Mercedes models. On some platforms start-stop is controlled by the CPC module, so an ECU file alone may not be enough. Mention the model in the order.
How to order the file
- Read the original file via OBD or on the bench. We need an unmodified stock file; bench pinouts are in the ECU pinout section.
- Upload it to the portal and select START STOP OFF. Other options can go into the same order.
- Get the finished file with recalculated checksums, on average within 30–60 minutes.
- Flash the file, clear faults and check at a standstill that the engine no longer shuts down.
Keep the original: to bring start-stop back, just flash the stock file.
Already have the file? Upload it to the portal and select START STOP OFF, the finished file arrives on average in 30–60 minutes.
Order Start Stop OffSupported ECUs for the START STOP OFF service
Frequently asked questions
Can start-stop be disabled permanently, so nobody has to press the button?
Yes. The ECU file blocks the automatic stop, so the system stays off after every new start. If a dealer later updates the ECU software, the change is lost.
Will there be fault codes or dashboard messages?
It depends on the car. Mention the model in the order and we will tell you how the button and dashboard messages behave on it.
Can start-stop be restored?
Yes, by flashing the original file. Always keep the stock file.
Can I fit a conventional battery instead of the AGM after the delete?
Better not. Charging is run by the car's energy management, which is set up for the factory battery type, and VARTA states plainly that a car with an AGM battery needs an AGM battery. A new battery still has to be adapted to the car.
Will fuel consumption go up?
Slightly in town and hardly at all on the motorway, because start-stop shuts the engine down at stops. Bosch puts the saving from start-stop at up to 5% in the NEDC cycle and up to 8% in its urban part.
Does start-stop harm the turbo?
After high-speed or heavy-load driving manufacturers advise letting a turbocharged engine idle for about a minute. An automatic stop right after the motorway or towing works against that, while with start-stop disabled the engine keeps running at the stop.
Why has start-stop stopped working on its own?
Usually because of the battery: on VW the function is blocked below 12.1 V of battery charge, and a replaced battery has to be adapted. Faults in any related module also keep it off.
Can Start Stop Off be combined with Stage 1 and other options?
Yes, everything is done in one file and one order.
How long does the file take?
On average 30–60 minutes.