Icon Start/Stop lights up yellow or red on the instrument panel when the automatic engine shutdown system (Stop&Start, ISS, MSA) detects a malfunction or operates in emergency mode. On Volkswagen Golf 4+, Skoda Octavia A7, BMW F30 and other models with this function, the indicator may be accompanied by the inscriptions START STOP MALFUNCTION or START STOP UNAVAILABLE. In 80% of cases, the problem is related to a discharged battery, oxidized terminals, or a faulty charge sensor - but there are also more serious reasons that require diagnosis.

If the icon is flashing red and the engine does not turn off automatically when stopped, the system is completely disabled due to a critical error. A yellow indicator without accompanying symptoms often means a temporary limitation of function (for example, when the temperature is low or the air conditioner is on). Before going to the service center, check battery voltage (should be ≥12.4 V) and the condition of the terminals - this eliminates the problem in half the cases.

What does the Start/Stop icon look like on different cars?

The appearance of the indicator depends on the make and model of the car, but the general principle is the same: it is a stylized letter "A" in a circle (from English Auto Stop) or a pictogram with the inscription START/STOP. Below are options for popular brands:

  • 🔴 Volkswagen/Audi/Skoda/Seat: Yellow or red circle with the letter "A" inside. Text may appear on the display START STOP FEHLER (error) or START STOP DEAKTIVIERT (deactivated).
  • 🔵 BMW/Mini: Green icon with inscription AUTO START STOP in normal mode, yellow/red - in case of failure. On iDrive a notification appears Start-Stopp-Funktion eingeschränkt.
  • 🟢 Ford: Icon with two arrows (up/down) and caption AUTO-START-STOP. If there is an error, it lights up orange.
  • 🟡 Renault/Nissan: Engine icon with a circular arrow. Message on screen: STOP & START UNAVAILABLE.
  • ⚫ Toyota/Lexus: Icon with the letter "S" in a circle (from Smart Stop). On hybrids can be combined with an indicator EV Mode.

On some vehicles (for example, Mercedes-Benz W205) the icon is duplicated by a text prompt on the display between the speedometer and tachometer. If the indicator is on constantlyand does not light up only under certain conditions (for example, when the heater is on), this indicates a malfunction.

How to distinguish normal system operation from an error

In good condition icon Start/Stop lights up green when the car stops (for example, at a traffic light) and goes out when you press the clutch/gas pedal. If the indicator yellow or red and does not change color when moving, the system is disabled due to:

  • Low battery charge (≤12.2 V).
  • Engine temperature sensor errors.
  • Malfunction of the generator or charging circuit.
  • Problems with the crankshaft position sensor.

On BMW 3 Series (G20) and Audi A4 (B9) When there are temporary restrictions (for example, when towing), the icon flashes yellow 3 times and goes out.

Top 5 reasons why the Start/Stop icon is on

According to statistics from service centers, 90% of calls for this indicator are related to five typical problems. You can diagnose them yourself without a scanner OBD-II:

Reason Symptoms How to check
Low battery The icon is yellow, the engine does not turn off automatically, the headlights are dim. Measure the voltage at the terminals with the engine off (should be ≥12.4 V).
Oxidized terminals Periodic shutdown of the system, problems with starting the engine. Remove the terminals, clean with sandpaper, check the tightness.
Generator malfunction The icon flashes red and the battery indicator on the panel lights up. Measure the voltage at idle (should be 13.8–14.4 V).
Temperature sensor failure The system does not work when the engine is warm or, conversely, when it is cold. Check the sensor readings using OBD-II (must match the actual temperature).
Clutch/Brake Pedal Position Sensor Error The engine does not turn off when stopped, the icon is constantly on. Check the system's response to pressing the pedals (the limit switch should click).

Critical error: If icon Start/Stop lit red simultaneously with the indicator CHECK ENGINE, check the charging circuit immediately. On Volkswagen Passat B8 and Audi Q5 this often indicates a broken alternator belt or failure of the diode bridge.

📊 Have you encountered the Start/Stop icon problem?
Yes, because of the battery
Yes, for a different reason
No, but the feature is manually disabled
I don't know what it is

How to reset the Start/Stop error without visiting the service

If the icon lights up after replacing the battery, a voltage failure, or temporarily disconnecting the terminals, try resetting the error yourself. To do this:

  1. Stop the engine and turn off the ignition.
  2. Remove negative terminal battery for 10–15 minutes.
  3. Reconnect the terminal, making sure there is a tight connection.
  4. Start the car and let the engine idle for 5-7 minutes.

On most cars (Ford Focus 3, Renault Megane 4) this is enough to reset the error. If the icon remains lit:

  • 🔧 Check it out Start/Stop fuse (usually located in the block under the hood, designated as ISS or MSA).
  • 🔋 Measure battery voltage under load (when starting the engine it should not fall below 10.5 V).
  • 🔍Connect OBD-II-scanner and find error codes P05XX (sensor circuits) or P25XX (Start/Stop system).

☑️ Checklist before visiting the service

Done: 0 / 1

Before going for diagnostics, follow these steps:

  • ✅ Check the battery voltage (must be ≥12.4 V).
  • ✅ Clean the battery terminals from oxidation.
  • ✅ Make sure the generator produces 13.8–14.4 V at idle.
  • ✅ Check the Start/Stop fuse.
  • ✅ Try to reset the error by disconnecting the terminal.
⚠️ Attention: On BMW 5 Series (G30) and Mercedes E-Class (W213) Resetting the error by disconnecting the terminal may lead to blocking of the multimedia system. In this case, you will need to enter the radio code.

Start/Stop error codes: decoding and what to do

If after connecting OBD-II-scanner you found errors related to the system Start/Stop, pay attention to the following codes:

Error code Description Possible reason Recommendations
P2500 Low battery level Discharged battery, faulty generator Charge the battery or check the generator
P2502 Battery temperature sensor malfunction Open circuit or sensor failure Check wiring, replace sensor
P2504 Start/Stop control circuit error Problems with the control unit or wiring Diagnostics in the service
P050D Low voltage on-board network Alternator or battery malfunction Check the charging circuit
P161A Incompatible battery The wrong type of battery is installed (for example, calcium instead of AGM) Replace the battery with the recommended one

By car Volkswagen Group (VW, Audi, Skoda) errors P25XX often accompanied by code U1113 - this indicates a loss of communication between control units. In this case it is required ECU flashing or replacing a damaged wiring harness.

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If the scanner shows an error P2500, but the battery is new, check it capacity and cold crank current (CCA). On vehicles with a Start/Stop system (e.g. BMW 1 Series F20) requires a battery with increased cycle resistance (AGM or EFB). Conventional lead-acid batteries fail after 6–12 months.

When can you drive with the badge on and when not?

If icon Start/Stop lit yellow and other symptoms (starting problems, dim headlights, errors CHECK ENGINE) no, you can continue to operate the vehicle. The system is simply disabled, but the main functions (ignition, charging, brakes) work fine.

Stop immediately and turn off the engine, if:

  • 🚨 Icon flashing red simultaneously with the battery indicator.
  • 🚨 A message appeared on the panel STOP START SYSTEM FAILURE or BATTERY DISCHARGE.
  • 🚨 The engine stalls when stopped or does not start the first time.
  • 🚨 The battery smells of acid or smoke is visible.
⚠️ Attention: On Hyundai/Kia with the system ISG (Idling Stop & Go) ignoring the red indicator Start/Stop may lead to battery completely discharged for 1–2 hours of parking. The car will not start without "lighting up".

If you notice that the icon only lights up under certain conditions (such as when the air conditioning is on or in traffic), it may be normal system behavior. On Ford Mondeo 4 and Opel Insignia B function Start/Stop automatically turns off when:

  • 🌡️ Engine temperature below +30°C or above +100°C.
  • 🔋 On-board network voltage is below 12.2 V.
  • 🚗 Travel speeds are less than 3 km/h.
  • 🔄 Frequent system switching on/off (more than 10 times per trip).

How to disable the Start/Stop system permanently (if it interferes)

If the function Start/Stop annoying or constantly turns off due to battery problems, it can be deactivated:

Method 1: Panel Button

On most cars, there is a button with an icon next to the gearshift lever or on the center console "A" in a circle. Press it once and the system will turn off until the next time you start the engine. On BMW and Mercedes the setting is saved between trips.

Method 2: Through the on-board computer menu

On vehicles with a multimedia system (VW MIB2/MIB3, Toyota Touch 2):

  1. Go to the menu Settings → Fuel economy.
  2. Select Start/Stop and set the value Off.
  3. Save your settings.

Method 3: Software Disable (Requires OBD-II)

To permanently disable you will need:

  1. Connect OBD-II-adapter (for example, ELM327).
  2. Use the program VCDS (for VW/Audi), ISTA (for BMW) or Forscan (for Ford).
  3. Find control unit 09 (Cent. Elect.) or 19 (CAN Gateway).
  4. On the menu Adaptation find parameter Start-Stop Deactivation and set the value 1 (disabled).
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Disabling the Start/Stop system via software may result in loss of warranty for cars under 3 years old. On Toyota Prius and other hybrids, this will also reduce the effectiveness of regenerative braking.

Frequently asked questions about the Start/Stop icon

Is it possible to drive with the yellow Start/Stop icon illuminated?

Yes, if there are no other symptoms (starting problems, battery drain). The system is simply disabled, but the car is fully operational. However, it is recommended to check the battery and alternator as soon as possible.

Why does the Start/Stop icon only light up in winter?

The system automatically turns off at temperatures below +3°C (on most cars) or if the battery does not have time to warm up. Also the reason may be deterioration of battery capacity in the cold. Check the battery voltage and replace it if it is older than 4-5 years.

How to reset Start/Stop error on BMW 3 Series?

On BMW F30/F35 You can reset the error like this:

  1. Turn off the ignition.
  2. Press and hold the button Start/Stop (on the gearshift lever) 10 seconds.
  3. Turn on the ignition without starting the engine.
  4. Wait 30 seconds - the error should clear.

If it doesn't help, use ISTA/D or BMW Scanner for diagnostics.

Which batteries are suitable for Start/Stop systems?

Vehicles with this feature require batteries of the type AGM or EFB with increased cyclic resistance. Conventional lead-acid batteries fail after 6–12 months. Recommended brands:

  • Bosch S5 AGM (for VW, Audi, BMW).
  • Varta Silver Dynamic AGM (for Mercedes, Ford).
  • Exide Start-Stop Plus EFB (budget option).
Why doesn't the Start/Stop icon go off after replacing the battery?

New battery needed "train" in the car system. On VW/Audi this is done through VCDS (block 19 → Adaptation → Battery Replacement). On BMW Battery registration is required via ISTA. Without this, the control unit does not recognize the container and turns off Start/Stop.