Have same issue. No ABS lite on , on my 2003 chevy Blazer. Most of the time when I brake the ABS comes on and there is never a ABS Lite. So which sensor could be bad? Also not that it is the ABS because I hear the pump come on.

  • It can be a bad lightbulb on the dashboard. Does the light turn on when you turn your key from off to on? – Baran Zadeoglu Jan 11 '19 at 17:47
  • Does the light come on when you turn the ignition on and the go out a few seconds after? What do you mean by 'Also not that it is the ABS because I hear the pump come on'? – Terry Gould Jan 11 '19 at 17:56
  • Yes, the lite tests good But is not active when vehicle is started. – Chas Jan 11 '19 at 18:11
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    ABS is activated and pump pulses brakes. No ABS lite comes on. if driving slow and braking straight ABS activates. – Chas Jan 11 '19 at 19:26
  • Ran a OBD code reader and viewed no ABS codes There is no Check engine lite active. – Chas Jan 11 '19 at 19:27

There are 4 things that can cause this:

Faulty ABS sensor

Fault reluctor ring

Bad wiring

Faulty ABS pump

You can do a visual inspection of the sensor, reluctor ring and wiring.

I've seen it quite often where the wiring has rubbed through and every now and again it touches the wheel or other metal object, the ABS ecu then sees this as the wheel being stopped so activates the ABS.

It is also quite common for corrosion to build up behind the ring, the ABS ecu also sees this as the wheel being stopped.

Sometimes but rarely it can be a fault with the pump/ecu.

Without any diagnostic equipment all you can do is inspect each corner one by one.

Ideally you need a diagnostic scanner and view live data, you will see one of the sensor speeds will drop out every now and again.

  • I will inspect all of this. Thank You . Will let you know what I find. – Chas Jan 11 '19 at 20:28
  • Along with the items mentioned by @ Terry Gould. I would add. A tire of different size from the others (either from wear or design), a caliper that is not working resulting in a variation of wheel speeds when braking, or a bad wheel bearing resulting in the timing ring moving away from the sensor. – mikes Jan 11 '19 at 21:33
  • @mikes - Along those lines, also if a sensor is loose and moving away from the reluctor ring will cause it the same way. Dirt buildup may cause issues as well. – Pᴀᴜʟsᴛᴇʀ2 Jan 11 '19 at 22:29

Low speed ABS triggering is likely caused by a rusty sensor ring.

As the wheel slows the signal from a rust damaged ABS ring becomes attenuated such that the ECU can no longer see the wheel spinning and thinks the wheel has locked.

With increased wheel speed the ferrous ABS ring is able to generate a significantly measurable signal as it passes across the magnetic pickup for the ABS. So I would recommend replacing if it looks in any way out of shape.

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