I have a 96 Avalon xls that had over 200K on it. When I start the car (usually when the engine is cold), the ABS light came on and stay on after the engine started. If I turn the car off and restart it again, the ABS light will go off after the car started. The ABS light never came on while I am driving but if it came on when I start the car, it will stay on until I turn the car off. Can anyone give me an idea of what is going on with the ABS light? Thanks in advance.
generally, the computer checks sensors at startup. it checks continuity, and that the sensor's resistance is within a certain range. before the car moves the computer can not check the functionality of the abs system 'cause that's based on pulses, picked up by the sensors on all 4 wheels.
in theory, abs is supposed to decrease brake fluid pressure to any wheel that is skidding. i don't know very much about it but i've heard people talk about an abs pump? maybe that would be a place to start, if the avalon system uses a pump?
In general, ABS systems run a quick set of checks at startup, and if any fails, the ABS function is disabled and the ABS light turned on. It will not rerun the tests until next startup, so the light should stay on, telling you there's a problem and you don't have ABS functionality.
There s/b a code available for a scanner to read, indicating what failed.
I have a 96 Avalon xls that had over 200K on it. When I start the car (usually when the engine is cold), the ABS light came on and stay on after the engine started. If I turn the car off and restart it again, the ABS light will go off after the car started. The ABS light never came on while I am driving but if it came on when I start the car, it will stay on until I turn the car off. Can anyone give me an idea of what is going on with the ABS light? Thanks in advance.
I understand all that, but why is the abs system failed the first time I start the car (usually when the engine is cold) and didn't when I turn it off and restart it again without doing anything else? If it failed the self test the first time, why didn't it failed again when I restart the car if there is indeed a problem with the abs system?
Well, if the ABS system is mechanically perfect and the ABS system's self diagnostics are wrong, then there's a problem with...the ABS system. Retrieving the codes will help pinpoint the problem.
First of all, what do I need to retrieve the code? I just found out that I don't even have to start the engine, I can just turn the key and all the warning light are on and then wait until they all go off after 5 seconds. If the abs light remain on after 5 seconds, it will still on after the engine started. I can turn it off without starting the engine and the abs light will goes off when I turn the key on again. It is really interesting but I still would like to find out if there is actually anything wrong with the abs system. Any help will be great to resolve this strange problem. As far as how long I have to leave the engine off before the abs light will stay on, it is very ramdom, but it usually takes a good 8 to 10 hours or overnight in order for the abs light to stay on the first time.
One possible scenario: The ABS actuator has an electric motor/pump that builds up pressure. When such things start getting old and tired, they take longer to reach specified pressure. Given a longer time to try, or a second chance (with the first try having built some amount of pressure less than specified), it can reach spec. How quickly the pressure dissipates after turning off the car????? If it holds for 12 hours, that could explain why a restart in 5 or 6 hours passes the ABS test.
Fair notice--the following is pure extrapolation:
I don't know the extent to which the system, when it operates, needs the pump to rebuild the "reservoir" in order to keep the ABS function operational for more than a second or two. If the need is high, a balky pump could mean it's possible ABS functionality could be lost in the middle of a skid it is working to control.
OK, I should have done this sooner, but I just opened a manual I have for an older GM ABS system. Among the conditions under which the warning lamp will be on:
- Before the accumulator is fully charged (when vehicles equipped with hydraulically assisted systems have been parked for a long time).
You need a scan tool that can communicate with the ABS computer.
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