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Q: ABS modulator and brakes activate under 3 mph.

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I have replaced all 4 speed sensors both rear hubs , right front axle, ABS controller, Modulator pump, Ignition switch , relays and checked all fuses ,front bearings are good cleaned the rust off the wheel speed sensor pads. I have been reading about the Yaw sensor and the main and secondary Transmission speed sensors and see that they are part of the system could they stop working under 3 mph ??. Trans shift evenly no jerking and speedometer works fine . The idle and speed increase are smooth. My scanner does not pick up anymore codes now ,they are all cleared with doing the work so far. But this problem does not go away . Any idea what else could cause this ,I cannot find this problem on the net anywhere .

My car has 160000 miles.
My car has an automatic transmission.

Hi there. If all of the components to the brake system has been replaced for the ABS system, then the transmission output shaft speed sensor could have failed. This speed sensor tells the driver what speed the vehicle is moving and it also tells the computer that the vehicle is in motion. The Yaw sensor is designed to measure the vertical access of the vehicle traveling on turns and elevations, like going over bumps, hill climbing, or controlling the traction control. It is also possible that the Yaw sensor has failed causing the traction control to fully engage making the brakes come on early. Test each sensor and then check to see which one has failed and replace it. If you need further assistance with your vehicle applying the brakes at 3 mph, then seek out a professional, such as one from Your Mechanic, to help you.

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