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Thread: Push Start starts the engine without foot on the brake

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    Push Start starts the engine without foot on the brake

    I'm not sure if this is the right section to post this. Let ne know if I have to move it somewhere else. I own a 2015 Mirage GLS CVT hatchback. The push start button used to work just fine (engine starts only if foot is on the brake).

    I had it serviced a week ago. They cleaned all 4 brakes, replaced front pads and bleed the dark fluid out of the system.

    3 days after the maintenance, I used the car again and I noticed that It started right away after just pushing the button once. I tend to go to Acc and ON mode first before starting the engine so I don't step on the pedal right away. I repeated it many times and it keeps starting right away.

    Here's what I did so far to check/fix:
    1) Took out some fluid in the master cylinder (previously, fluid was a bit over the max line)
    2) checked brake light switch; have no issue with it because brake light is fine, off when pedal is not pushed; tried disconnecting the switch and starting the car, still the same

    It seems that the computer is getting the signal that brake is pushed and that's why it keeps starting. I'm not sure where else to look. Does the ABS system has to do with it? What could have the mechanic inadvertently changed/damaged that can cause this?



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    I have neither an AS&G nor an automatic, but I would do this:

    Check the brake switch again, it should actually be two switches in one case. One for the brake light, another one for the ECU (ECM) which is needed for proper AS&G starting.
    The switch has a plunger (tip) on it pushing on the resting brake pedal, the plunger going out of the switch when the pedal is pushed. Maybe the switch is a little bit too far away from the pedal? Have a good look, adjusting is easy! For testing, one person could push the plunger by hand and the other pushing the start button. Good luck!

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    I went further with checking the brake light switch. I removed it from the connector, took it out and checked for continuity. I noticed that two terminals for the brake light are connected when the plunger is released (i.e. pedal is pressed). For the ECU terminals, it's the opposite. Terminals are connected when plunger is pushed (i.e. pedal not pushed).

    With the brake light switch out of the equation, I took a small jumper wire and shorted the rear light terminals in the connector and as expected, they lighted the whole time. I removed the jumper wire and shorted the ECU terminals this time and tried pushing the Start button, and engine started right away. Removing the jumper did the same engine fast start.

    Is my brake light switch faulty? Is its sequence correct?

    PS: With the wire jumper on brake light connectors, I did not try starting the engine. Missed a significant test there . I can't try again until tomorrow due to work.

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    Congratulations on your findings!
    The next step would be to check the mechanical adjustment of the switch assy.

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    At, first my first suspect was the switch because I remembered the mechanic pumping the brake pedal hard during the fluid bleed process (used 2 liters of fluid overall). I thought the switch took a beating from that. However, I just tried (got home early) disconnecting the switch, put a wire jumper in the light connector to simulate a pressed pedal (lights on all the time), engine started right away. I took out the jumper so it's just the bare connector and still the same. With this, I can say that the switch is not the culprit here.

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    Sorry I can't help further.
    I would just in case look at the wiring. Maybe something torn, broken? Include the connectors behind the grey panel to the left of your left foot, and take a very close look at the crimped connections. Strangest things can happen there, see other threads.
    Good luck!

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    Yeah, I'm kinda lost as well. Could have been simpler if it was just the switch. Thanks anyway.

    Oh, I also OBD scanned and returned no codes. I'm not sure if that's already good enough as for tracing shorted and/or broken connections. Manually checking those small wires, wrapped in tapes and all will be challenging af.

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    Quote Originally Posted by Cool Silver View Post
    Yeah, I'm kinda lost as well. Could have been simpler if it was just the switch. Thanks anyway.

    Oh, I also OBD scanned and returned no codes. I'm not sure if that's already good enough as for tracing shorted and/or broken connections. Manually checking those small wires, wrapped in tapes and all will be challenging af.
    you can always try and use the factory service manual that can be found on this site to determine the other end of the wires location and use a multimeter to test for continuity to see if it is broken and or shorted?

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    Senior Member Mitz's Avatar
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    @Cool Silver,

    From your description - the brake light switch is normally-open (NO) while the ECU switch part is normally-closed (NC). This makes me think one of the wires of the NC switch has an open connection. You might try to take a voltage measurement with a digital multimeter on their respective terminals while the start button is on ACC/ON mode and compare it while you alternately press/depress the brake pedal - the measured value should not be the same if the wiring connectivity is good.

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    Just taking a wild guess here, by any chance did they replace any of the tail/brake light bulbs when you had the service done on your car? It appears from the electrical diagrams in the service manual that the ecu monitors the brake light circuit for pushbutton starting purposes. So the ecu sees the voltage applied to the brake lights and decides it's ok to start the engine. If the wrong bulb was installed in the tail/brake light socket or was incorrectly plugged in, the tail light voltage could leak into the stop light circuit and fool the ecu into thinking the brakes are applied and it's ok to start the car. For this to happen though you would have to have the headlight switch in the on position when you are starting the car. It looks like the other part of the brake light switch is used to cancel the cruise control or some other purpose, at least in the service manual I am looking at. As I said this is just a wild guess.



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