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Q: ABS comes on under 3 mph and when starting out

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I have replaced all 4 speed sensors both rear hubs , right front axle, ABS controller, Modulator pump, No codes come up ,front bearings are good . I have been reading about the Yaw sensor and the throttle position sensor and see that they are part of the system .. 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.

A: Hi there. When this occurs I usually instal...

Hi there. When this occurs I usually install my scan tool to check the inputs from this system. From what you are explaining it sounds like you have replaced many of the sensors. You need to also make sure that all of the tires are exactly the same. If they are then the yaw sensor needs to be checked and the TPS needs to be checked. Most of the time it is caused by the yaw sensor. It can also simply need to be reprogrammed. If you need to have this ABS system checked out, consider YourMechanic, as a certified mechanic can come to you to [diagnose why the ABS light is coming on] https://www.yourmechanic.com/services/abs-light-is-on-inspection

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A: Hi there. I have a few things that you can ...

Hi there. I have a few things that you can check that may be the cause of the ABS light coming on momentarily at the slow speed. Are the tires all the same size? I know this one seems obvious, but it does happen. Check all of the speed sensor connectors for fit. Check the ABS connections that are accessible for fit and corrosion. Check the battery terminals for fit and corrosion. Check the battery with a digital battery tester that provides current voltage, cold cranking amps, and state of health. The battery is the heart of the electrical system and can have a direct affect on anything electrical; the ABS system is very sensitive to electrical disturbances. Check alternator output at idle and under load. If the output at idle is low, this could be causing your light to come on with no codes. This happens because once you get moving the alternator output is sufficient, the code goes away; the system is operating normally at this point. I have seen an alternator problem cause ABS lights to come on and watched the technician diagnosing this condition literally pull his hair out over it due to it being that frustrating. An intermittently failing brake light switch could cause the light to come on and be difficult to test. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts and pulling your own hair out. Your Mechanic has several available technicians that can assist you with an ABS light is on inspection.

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