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Jim Grant's Tech Tips
‘95 Toyota Camry LE, Many ABS Sensors?
Q:
The ABS light came on and has since gone off after the shop replaced my right front ABS Wheel Speed Sensor. Since that replacement and other costly repairs, including a left front axle from an open CV boot, I'm having a braking problem. When braking and turning at the same time coming to a complete stop, the brakes seem to let go and grab a second later. I am able to stop but am concerned that it is unsafe. The garage is concluding that the other 3 wheel speed sensors are bad since they are not testing out correctly. Before replacing the front right, another garage had diagnosed the ABS light problem and that's the only one that turned up bad. Since the ABS light has gone off after that replacement, I'm thinking the new diagnosis might be a computer glitch. The garage is quoting me an additional $1000 to replace the other 3 sensors. They tell me they've had 5 or 6 other cars with the same problem already this year. Are they daft, very greedy, or very smart?
- Amy
A:
At first one would think that they're daft and just want to take your money, but beware the crazy man may be speaking the truth. I got a headache from a Toyota's ABS system that did make me daft. For some strange reason the ABS sensors on your Toyota can fail if you look at them wrong with your safety glasses on. The more automotive inclined readers are now saying I'm daft, but there is nothing like the school of hard knocks to make a crazy man speak the truth. In addition, I'm not the only crazy man when it comes to Toyota ABS sensors. The ABS sensors in your vehicle are very sensitive, so sensitive that when we're replacing an axle joint or front-end part that requires a hammer the sensor will be removed and placed safely to a side. I'm not talking hitting the sensor with a hammer causing the problem. It is the vibration the hammer seems to cause that will cause the sensor to go daft after the repairs. Sometimes they go daft on you just removing them and reinstalling them. But, there is one thing that is bugging me just a bit and you should have checked out. If the brake is releasing and then grabbing at low speeds when turning you may not need all of the sensors. It may be worth your checking account to have a few checks of the ABS system performed. Have the ABS system temporally disabled for diagnostic purposes. Try to recreate the braking problem. If the problem cannot be recreated enable the ABS system and confirm the condition returns. If the condition returns, I'm willing to bet that it occurs more often in one direction than another. If I'm right, have the repair shop check the voltage signal from the wheel speed sensors. The voltage test has to be performed with a high quality multi-meter or lab scope. Check for a difference of amplitude from the sensors. I know this is a bit techie but that coffee you'll own me will taste good. The tech is likely going to find that there is a variance in amplitude in the area of 100 to 200 millivolts difference in the sensors. The sensor with the low value is miss-positioned (not close enough) to the toner ring or it needs to be replaced. The ABS computer thinks the difference is not a problem, so there will be no light or code. For a second cup of coffee the crazy man believes that the left front wheel speed sensor will be the problem. Why? You need to hit stuff with a hammer when replacing a left front axle. The tech must have looked at the sensor wrong.
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