When start engine, after few seconds or when we shift gear why does ABS light turn on?

The sensor cuda gut dirty or damagd...tell mechanic. Chec fluid level and condition. Or unhook batt a min to see if systemreboots

Brake light switch problem may cause the ESP / BAS lights to illuminate.

Common symptoms of a bad
Mercedes brake light switch.

• Car stuck in Park.
• ABS ESP ETS lights come on.
• Can not move the shifter from Park to Drive.
• Brakes Defective Warning on Instrument Cluster
• Car won't shift gears. Stuck in 2nd gear, limp mode.
• Brake lights don't work. (Brake light switch can still be defective even if the brake lights work. Checking the brake light operation is not a good test.)
• ESP, BAS, ABS lights turn on. Car won't shift properly. Stuck in gear.

TEST: To test your new brake light switch: Turn you car off to reset the ABS light. apply the parking brake. and start the car in neutral or park without using the brake. if the problem is the brake light switch... the light will only come on when you press the brake pedal.

If you replaced the brake light switch and the light is still on you should check a few other things such as:

• Fuses and Relays
• ABS pump
• ABS wheel speed sensor
• Brake Fluid Level
• Get an advanced scanner to read trouble codes.

NOTE: ** You may need a MBZ scan tool to reset the error code which was stored in the ECU because of the bad brake light switch.

1) try to use the self diagnose.
2) place ignition swtuch in the start position, the lights coming on
3) engine starts, the brake light sould turn off inmediately. the ABS ligth will illuminate for aprox 6 seconds.
4) test drive the vehicle at speed above 20mph for a few minutes. during the test the both test lights should remain off, if any one of the warninign light utron, take note of the condition.
5) stop the vechicle using the braking pressure.both light should remain offf during the stopping procedure.
60 place the gear selector in to PARK, and observe the warning lights, they should both be off.
God bless you

look under the truck at the ****** and check the wiring to the sensors if good may be a bad sensor,also check the wiring and connections to the abs wheel sensors [ located from frame to the hub behind the rotors ] the abs also acts as speed sensor if problem was with an abs sensor at the[ hub] wheel usually set the brake system to normal power brakes [if u hit brakes hard will lock up or skid wheels] with the abs light coming on if the speed sensor at ****** malfunction can and usually causes shift problems

Hi Peters6709,
Sorry to tell you, but you need to replace the pad-wear sensors as well. They are the little trapezoid pieces that hang inside the tops of the inside pads. They should run about $10 each. Once replaced, disconnect the battery completely for about 10 minutes, if you have a stock radio keep the code handy.

Next time check the pads every 10-12K miles. I have been running the SAME pad wear sensors on my Z3 for the past 2 pad changes now after making the same mistake the first time.

Best of luck!

i know this may sound strange but remove the brake fluid cap. on the cap is a sensor, do this away from any other vehicle and yours and shack the sensor by the cap a good few times. as fast as you can. then re fit the sensor see if the lights go off. sometimes it works sometimes not. this just because the brake light is on, this only usually comes on when the sensor thinks there is low brake fluid. and it can also tell the abs as well. and this is why both the lights are on. also make sure the fluid is at full markings.

Check engine light on?

Is it a manual or auto? Assuming its a manual, is there an ABS light on? If so or if you hace changed the brake pads recently or even had the tires off or rotated, there could be a problem in the brake pad sensor or abs wheel speed sensor.

Check with Porsche service (your closest dealer) for recalls or TSB (Technical Service Bulletins) related to your concern and check the cayman/boxster owners clubs for similar posts and resolutions.

Hope that helps.

Ok the reason I ask is that will help to pinpoint the concern. See ABS system when you first turn the ignition on will do a self test on itself,light turns on for a few seconds then turns off if everything proves out. Then when you start driving once you reach about 12 mph it will activate the pump and perform a 2nd self test.If everything is ok light stays off,if it see's a problem it turns on the light and disables the ABS.
Since yours comes on after you start driving then problem is most likely a wheel speed sensor concern. Since you just did a rear brake job and the problem started after this I would say it is one of the rear sensors.You need to look at the sensors and make sure the sensor and ring look ok and that you didn't get grease or dirt in the teeth of the sensor ring or maybe bent the end of one of the sensors and make the gap larger between sensor and ring.

Ok, check the brake fluid level for a start. This could mean a few things. Your brake pads might be worn down, which would bring a yellow warning light on(triangle), at the same time with the pads being low it will have displaced the fluid, making the level low, this would be a red light on. Now because of this the body control module has detected these faults, will have turned the abs off, hence the abs light.
If brake fluid is low, this could confirm my theory.
If its low, top up with dot 5 brake fluid and take to garage to have new pads fitted.

TL

Rear Sensor replacement 44.95 retail
Shop Labor 60.00
This will fix the ABS and Brake lights, will fix the speedometer isue and smooth out the erratic shifting.