See also my original post about replacing the driver seat in a Renault Kadjar.
WARNING: Disabling the Start/Stop system could be illegal, because the car's approval is based on the security features and environmental equipment of the engine.
The Start/Stop system
The Start/Stop system in ICE cars is a (somewhat disputed) method to save fuel. Under the right circumstances the engine will be stopped, and started again to continue the journey. This system has a couple of (dis-) advantages:
Advantages:
- Fuel saving. There are unverified claims that the Start/Stop system could save up to 1% fuel. IMHO this is not a realistic value, but might be achieved in very specific scenarios for a limited number of cars
- Noise reduction while waiting
Disadvantages:
- Delayed start because of waiting for the engine to start and to deliver torque
- Complex list of events when the engine can be stopped (or not). Extremely hard to predict when the engine will be stopped
- Different implementations of the Start/Stop management system per car brand, even per car type
- Additional wear and tear of the start motor and battery
- Likely wear and tear of engine components that require oil pressure (turbo and other moving engine parts)
After MOT requirements research in UK and EU, it seems that the Start/Stop system is not part of an MOT rejection, UNLESS a warning/error light is shown. So when the Start/Stop system is disabled and there are no errors/messages shown during MOT, the car will pass.
Disabling the Start/Stop system
The Start/Stop system in Kadjar is using the Seat Pressure Sensor and the Seat Belt switch to determine if a driver is sitting in the car.
When BOTH sensors are engaged the Start/Stop system MAY work, depending on many other factors. When the Seat Belt is not used and/or there is no one in the driver seat, the engine will NOT be stopped or started by the Start/Stop system. This to prevent that the car will move without a driver. In later models, the use of the Seat Pressure Sensor is abandoned, so only the Seat Belt switch is used to enable the Start/Stop system.
So, in this case, we can use the Seat Belt Pressure sensor to disable the Start/Stop System. The Seat Pressure Sensor has 2 values: 2200 Ohm when no driver is in the seat, and 200 Ohm when there is a driver is in the seat.
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Kadjar Seat Pressure Sensor resistor values |
In my original post I suggested to use a 200 Ohm resistor to make the car think that the driver is sitting in the car, and allow the Start/System to work. However, when we use the 2200 (2k2) Ohm resistor, the car assumes that there is no driver in seat (which is a valid status), and the Start/Stop system will NOT be engaged. This is a safe configuration. The Start/Stop system is disabled, and there are no warning signs on the dashboard. The car will pass MOT.
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The dummy resistor looks like this, and is shrink wrapped in the final solution (see the original post, where the 200 Ohm resistor is shown). Important: the pins of the dummy should be 0.8mm. This to prevent damage to the original car connector.
In short: replace the 200 Ohm resistor by a 2k2 Ohm resistor.
For other cars/seats take the next approach:
1. Check if there is a Seat Pressure Switch under the drivers seat
2. Find the Seat Pressure Switch connector and disconnect the sensor
3. Start the engine and check for a Start/Stop system error message. If so, we can use the Start/Stop system connector to disable the Start/Stop system. If not, you need to find another method.
4. With no person in the driver seat, measure the resistance of the Seat Pressure Sensor.
5. Use the measured value to make the dummy resistor.
6. Apply the dummy resistor provisionally and check that there are no error messages. if no errors, finish the dummy resistor. Make sure the connector fits well and tie wrap the cable and connector to prevent lying around. If still an error, recheck the resistor value with and without a person in seat.
In case the car is rejected with the MOT:
Remove the dummy and reconnect the original connector.
In case you want to enable/disable the Start/System:
Make a dummy with a switch and the two resistor values, to enable/disable the Start/Stop system, in both cases without an error message on the dashboard.
