My friend has a '94 Camry with 4 wheel ABS, and when the brakes are applied at low speed you hear a thumping noise in the front end drivers side.
Both axles are good and have the sensor ring. Both ABS sensors have been replaced, and it still made no difference.
But, when you unplug either front ABS sensor the thumping noise stops but of course the ABS light is now on-on the dash. When you plug either sensor back in the thumping starts back up.
Any ideas???
Thanks a bunch Chas
Does the thumping noise vary with wheel speed? Is it a rapid vibration like the ABS activating? Is it felt in the pedal?
Two obvious possibilities:
First I would check the sidewalls for the size of all four tires (need to be the same), and compare tread depth. To go a step further, I might check the rolling distance of all of my tires by marking them with fresh paint, rolling the car forward until the two paint marks leave spots on the ground, then refreshing the same spots on the tires and rolling the tires until the paint marks are left on the ground once more. Without disturbing the paint on the ground, measure each pair center-to-center and compare all measurements (should all be very close).
If there is an electric/hydraulic failure that doesn't cause the ABS ECM to enter failsafe, the system may be operating any time the brake pedal is pressed. Usually this is a wheel speed sensor or tone ring issue. They do not always "set a code" or cause the ABS system to shut down. I am leaning towards this type of failure as I would suspect that you have checked tire sizes already. Of course, I have actually seen a worthless "mechanic" hang a high $$ EHCU/modulator assembly on a Prius that really only had one wrong sized tire. After he ordered and installed the part I decided to tell him what the real problem was. I would have helped him earlier, but this is the way he has always "diagnosed", yet seemingly he'll never get fired. Rant/job hatred over. Sorry.
Toyota MDT in MO
Thanks for the info guys. I'll pass it along to my friend. Hopefully it's something simple like the wrong size tires.
Chas
No it only does it as you are slowing down like under 20 mph. It's a definite thump thump thump noise coming from the front drivers side. I beleive the thumping slowed as the vehicle slowed down. Not sure if he feels it in the pedal or not.
Chas
If it goes away when you unplug a speed sensor, I can't help but believe it is a purely ABS related issue. The system will default to standard hydraulic braking and turn on the ABS light, which sounds like your description.
Toyota MDT in MO
Problem solved! BOTH ABS sensor rings had a nick in them causing the thumping. Once replaced the problem is now gone.
Thanks for everyone's help Chas
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