ABS isn't working.
12-09-2005, 12:26 PM
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ABS isn't working.
I have a 2000 Civic Ex and my ABS isn't working. There's a lot of snow in my area right now, and when I slam on my brakes at about 30+ my wheels lock up. My ABS light isn't on. Anyone know what could be wrong?
12-09-2005, 02:39 PM
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Re: ABS isn't working. (Cone_420)
The ABS System for your Civic calculates the difference between "Vehicle Speed" and "Wheel Speed", and makes any necessary adjustments by modulating the Brake Hydraulics.
From the Helm Service Manual 96-00 Civic (p 19-47)...
"The ABS control unit detects the wheel speed based on the wheel sensor signal it received, then it calculates the vehicle speed based on the detected wheel speed. The control unit detects the vehicle speed during deceleration based on the rate of deceleration."
Basically, the only way your car can tell if your brakes are locked up is by checking the spin rates at each corner. If one corner is decelerating at a quicker rate than the others, the ABS system can adjust the pressure applied to that caliper (and others, if necessary) until it is more even.
When driving in snow or on ice, or on any other very slick surface, the force of your brakes clamping on your wheel (rotor) will usually be a lot greater than the force of rolling friction (from the ground) that wants to keep your wheel spinning. When that is the case, your wheels will lock up, and much more easily than when driving under normal (dry) conditions. Under snowy or icy conditions, how is your vehicle going to detect any difference in Vehicle/Wheel Speed if all 4 corners are locked up?
... It can't. When you have 4 wheel lockup in icy conditions, your ABS system thinks your Vehicle Speed is 0mph. Since the wheels are not moving, it also thinks that the Wheel Speed is 0mph. Because of this, ABS will not "activate", and you receive no benefit from its "use".
The bottom line is not to rely on ABS under very slick conditions (under ANY conditions, for that matter). When driving in snow or ice, there is much smaller of a "Braking Pressure" range for which ABS will be effective (since your wheels lock up (and stay locked) easier). Slamming on the brakes in slick conditions will effectively negate any benefits of ABS... Proper Brake Modulation is the key, as ** there needs to be a calculated difference between Vehicle Speed and Wheel Speed, and ice/snow just won't provide enough friction to create this difference. **
I must mention first that I DO NOT HAVE ABS on my current vehicle. As such, I readily admit that there things I don't know, as well as things I know incorrectly. If anyone has any corrections or other important details, please contribute. Everything I know about ABS has been based on studies of the Helm Service Manual, and a few posts here and there...
Next time you get in your car and before you start it, keep an eye on your ABS Indicator Light in your Dash Cluster. If it starts blinking, note the blink pattern (that will be your ABS Trouble Code) and report back what you found. If your ABS light doesn't blink, then your ABS system is fine... You simply pressed too hard on the brakes in ice...
Drive safely, and let us know if there's anything else wrong (ABS Code(s))!
JasonGhostz
From the Helm Service Manual 96-00 Civic (p 19-47)...
"The ABS control unit detects the wheel speed based on the wheel sensor signal it received, then it calculates the vehicle speed based on the detected wheel speed. The control unit detects the vehicle speed during deceleration based on the rate of deceleration."
Basically, the only way your car can tell if your brakes are locked up is by checking the spin rates at each corner. If one corner is decelerating at a quicker rate than the others, the ABS system can adjust the pressure applied to that caliper (and others, if necessary) until it is more even.
When driving in snow or on ice, or on any other very slick surface, the force of your brakes clamping on your wheel (rotor) will usually be a lot greater than the force of rolling friction (from the ground) that wants to keep your wheel spinning. When that is the case, your wheels will lock up, and much more easily than when driving under normal (dry) conditions. Under snowy or icy conditions, how is your vehicle going to detect any difference in Vehicle/Wheel Speed if all 4 corners are locked up?
... It can't. When you have 4 wheel lockup in icy conditions, your ABS system thinks your Vehicle Speed is 0mph. Since the wheels are not moving, it also thinks that the Wheel Speed is 0mph. Because of this, ABS will not "activate", and you receive no benefit from its "use".
The bottom line is not to rely on ABS under very slick conditions (under ANY conditions, for that matter). When driving in snow or ice, there is much smaller of a "Braking Pressure" range for which ABS will be effective (since your wheels lock up (and stay locked) easier). Slamming on the brakes in slick conditions will effectively negate any benefits of ABS... Proper Brake Modulation is the key, as ** there needs to be a calculated difference between Vehicle Speed and Wheel Speed, and ice/snow just won't provide enough friction to create this difference. **
I must mention first that I DO NOT HAVE ABS on my current vehicle. As such, I readily admit that there things I don't know, as well as things I know incorrectly. If anyone has any corrections or other important details, please contribute. Everything I know about ABS has been based on studies of the Helm Service Manual, and a few posts here and there...
Next time you get in your car and before you start it, keep an eye on your ABS Indicator Light in your Dash Cluster. If it starts blinking, note the blink pattern (that will be your ABS Trouble Code) and report back what you found. If your ABS light doesn't blink, then your ABS system is fine... You simply pressed too hard on the brakes in ice...
Drive safely, and let us know if there's anything else wrong (ABS Code(s))!
JasonGhostz
12-09-2005, 04:02 PM
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Re: ABS isn't working. (JasonGhostz)
JasonGhosts is right. You're probably experiencing a 4-wheel simultaneous lockup.
To test the ABS, drive the car with one side on snow/ice and the other side on dry pavement...this can usually be accomplished easily after a snowstorm and after the road has been plowed, just drive real close to the edge of the road so the right side wheels are on slick snow and the left side wheels aren't. Do this in a safe place at a speed of 25-35mph. Then slam on the brakes...you'll feel the pedal get hard and pulsate, you'll also hear the ABS unit engage if the ABS works.
If the wheels still lock up, you're gonna have to take the car to a shop with a scanner that can read the ABS computer for diagnosis, anything other than that would be little more than an educated guess.
To test the ABS, drive the car with one side on snow/ice and the other side on dry pavement...this can usually be accomplished easily after a snowstorm and after the road has been plowed, just drive real close to the edge of the road so the right side wheels are on slick snow and the left side wheels aren't. Do this in a safe place at a speed of 25-35mph. Then slam on the brakes...you'll feel the pedal get hard and pulsate, you'll also hear the ABS unit engage if the ABS works.
If the wheels still lock up, you're gonna have to take the car to a shop with a scanner that can read the ABS computer for diagnosis, anything other than that would be little more than an educated guess.
12-09-2005, 05:31 PM
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Re: ABS isn't working. (anony95ex)
Sorry To steal thread, in the summer time someone cut me off.. and I had to slam brakes on and abs came on pedal pulsated.. and the light came on..... today driving in the snow, some person braked in front of me so I switched lanes, but my car started to slide in the snow, and I put on brakes, it just pulstated vary fast.... it seemed like ABS was on but... the light never showed...
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