| Posts: 325
| Joined: 09/10
I was having a problem with the Cavalier brakes, the front, grabbing really hard. It did lock up the front very easily. New pads, and this problem seemed to go away. it Brakes solid and stops smooth. But I still had the ABS lights on. A common problem with the Cavalier.
Funny thing did happen. I left the car parked at the train station for 3 days. When I started the car, ALL the brake lights were off. No ABS warning, no brake indicator, etc. I backed up, hit the brakes lightly. Drove forward a slight bit, hit brakes- ABS warning and the brake indicator lights came back on. Now could this be something in the master cylinder or ABS unit? Like something loosened up and released back to rest position just sitting there for 3 days? Seems like something sticking. I'm not too familiar with the ABS unit so I am reading about it. I'm also going to order one of those ABS scan tools thru ebay, taiwan made. It's about $20 so worth the gamble.
find a scan tool that will read ABS scan codes.. not all the generic scan tools will
you might want to examine the abs speed sensor wiring to the front wheels..
if you have chance... take a look at the tone rings and the end of the sensors on the front if exposed ... sometimes you have to remove the sensor from the spindle to examine the end for excessive brake dust build up around the magnet..
the ABS system uses 3 or 4 speed sensors at the wheels... 3 sensor on a rear wheel drive on a GM is usually just behind the rear end yoke in the rear end housing... counts the speed of the pinion ...
as the car speeds up or slows down the speed sensors create voltage... when you step on the brake.. the brake light switch tells the ABS computer that you are braking.. so it starts active control...
if any of the sensors voltage drop more than the others... it isolates that wheel from the master and releases the pressure to that wheels brake to attempt to regain traction.... the antilock computer can isolate... reduce or increase pressure to each wheel...
there was an issue back in the 90s usually on this same brand of pick up... where usually the right front wheel speed sensor went bad or had a broken wire... for some reason.. it would create higher voltage spikes into the system.. this would tell that this wheel is moving faster than the others... and would isolate the other 3... leaving the car owner with MINIMAL or one wheel braking..
access the codes... post them ... google.. them.. check the AZ site..
there are just so many things that could be wrong.. including low brake fluid level... rusty tone rings.. sensors covered with brake pad and rotor dust... broken sensor wires... i found some that were hit by the tire.. twisted into a candy cane...
| Posts: 325
| Joined: 09/10
Thanks. Good info. I have found particles stuck to it magnetically before. I blow all that stuff out. But the ABS has been an issue for a long time. Reservoir is filled. And didn't see any broken wires. But will look more closely next time I pull the front wheels.
so many things to check...
be sure to check for rusty tone rings...
you can hook a digital volt meter to the disconnected wheel speed sensors and spin that tire.... see if you get DC volts and AC volts... you might actually try it on the Hz setting also. i usually don't mess around with antilocks so i am hanging in theory on how they work...
the AZ site does cover a lot of the testing on them.
you will want to read that section on bleeding and flushing the system..
you can always just unplug the power wiring to the top of the unit and revert to NON abs brakes...
when you replace pads.... use a small pair of long nose vice grips and lightly but firmly pinch off the brake hose (rubber section) to that caliper.. that prevents any fluid from moving backward through the very expensive control head.. . use a C clamp or piston retractor that holds position.. loosen the bleeder screw as you start to retract... close it as you reach the back of the bore.. do not loosen the retract tool until you have tightened the bleeder screw.. this prevents the Cooked fluid from being forced backwards through the multiple motorized master cylinder devices in the control head.. there are also tiny valves that can get crap stuck in them.. holding them effectively closed.. or open.. allowing brake fluid to enter when it should not..
this is a anti slid valve from most fords.. you might be able to visualize the flow better.. RWAL.. rear wheel anti locks..
isolation valves block flow to and from the master as motorized accumulator pistons control the pressure to the wheel cylinders and calipers.. this is only when the ABS light is on.. showing that the system is ACTIVATED...
if you light comes on.. only when you step on the brakes.. and then goes out.. when you release.. you may NOT find any codes as the system thinks the system is working properly..
C0000 - Vehicle Speed Information Circuit Malfunction
C0035 - Left Front Wheel Speed Circuit Malfunction
C0040 - Right Front Wheel Speed Circuit Malfunction
C0041 - Right Front Wheel Speed Sensor Circuit Range/Performance (EBCM)
C0045 - Left Rear Wheel Speed Circuit Malfunction
C0046 - Left Rear Wheel Speed Sensor Circuit Range/Performance (EBCM)
C0050 - Right Rear Wheel Speed Circuit Malfunction
C0051 - LF Wheel Speed Sensor Circuit Range/Performance (EBCM)
C0060 - Left Front ABS Solenoid #1 Circuit Malfunction
C0065 - Left Front ABS Solenoid #2 Circuit Malfunction
C0070 - Right Front ABS Solenoid #1 Circuit Malfunction
C0075 - Right Front ABS Solenoid #2 Circuit Malfunction
C0080 - Left Rear ABS Solenoid #1 Circuit Malfunction
C0085 - Left Rear ABS Solenoid #2 Circuit Malfunction
C0090 - Right Rear ABS Solenoid #1 Circuit Malfunction
C0095 - Right Rear ABS Solenoid #2 Circuit Malfunction
C0110 - Pump Motor Circuit Malfunction
C0121 - Valve Relay Circuit Malfunction
C0128 - Low Brake Fluid Circuit Low
C0141 - Left TCS Solenoid #1 Circuit Malfunction
C0146 - Left TCS Solenoid #2 Circuit Malfunction
C0151 - Right TCS Solenoid #1 Circuit Malfunction
C0156 - Right TCS Solenoid #2 Circuit Malfunction
C0161 - ABS/TCS Brake Switch Circuit Malfunction
C0221 - Right Front Wheel Speed Sensor Circuit Open
C0222 - Right Front Wheel Speed Signal Missing
C0223 - Right Front Wheel Speed Signal Erratic
C0225 - Left Front Wheel Speed Sensor Circuit Open
C0226 - Left Front Wheel Speed Signal Missing
C0227 - Left Front Wheel Speed Signal Erratic
C0229 - Drop Out of Front Wheel Speed Signals
C0235 - Rear Wheel Speed Signal Circuit Open
C0236 - Rear Wheel Speed Signal Circuit Missing
C0237 - Rear Wheel Speed Signal Erratic
C0238 - Wheel Speed Mismatch
C0241 - EBCM Control Valve Circuit
C0245 - Wheel Speed Sensor Frequency Error
C0254 - EBCM Control Valve Circuit
C0265 - EBCM Relay Circuit
C0266 - EBCM Relay Circuit
C0267 - Pump Motor Circuit Open/Shorted
C0268 - Pump Motor Circuit Open/Shorted
C0269 - Excessive Dump/Isolation Time
C0271 - EBCM Malfunction
C0272 - EBCM Malfunction
C0273 - EBCM Malfunction
C0274 - Excessive Dump/Isolation Time
C0279 - Powertrain Configuration Not Valid
C0281 - Brake Switch Circuit
C0283 - Traction Switch Shorted to Ground
C0284 - EBCM Malfunction
C0286 - ABS Indicator Lamp Circuit Shorted to B+
C0287 - Delivered Torque Circuit
C0288 - Brake Warning Lamp Circuit Shorted to B+
C0290 - Lost Communications With PCM
C0292 - Lost Communications With PCM
C0291 - Lost Communications With BCM
C0297 - Powertrain Configuration Data Not Received
C0298 - Powertrain Indicated Traction Control Malfunction
C0300 - Rear Speed Sensor Malfunction
C0305 - Front Speed Sensor Malfunction
C0306 - Motor A or B Circuit
C0308 - Motor A/B Circuit Low
C0309 - Motor A/B Circuit High
C0310 - Motor A/B Circuit Open
C0315 - Motor Ground Circuit Open
C0321 - Transfer Case Lock Circuit
C0323 - T-Case Lock Circuit Low
C0324 - T-Case Lock Circuit High
C0327 - Encoder Circuit Malfunction
C0357 - Park Switch Circuit High
C0359 - Four Wheel Drive Low Range (4LO) Discrete Output Circuit
C0362 - 4LO Discrete Output Circuit High
C0367 - Front Axle Control Circuit High
C0374 - General System Malfunction
perhaps the list above is for a different system
The diagnosis of the ABS system is rather complex and requires quite a few special tools including scan tools, special test harnesses and other special and expensive tools. Alternative methods and common sense can be substituted, however, It is beyond the scope of the average do-it-yourselfer. If you experience the amber ABS light on in the instrument cluster of your vehicle, check the fluid level in the master cylinder first. Low fluid level will usually illuminate the amber ABS light as well as, but not always, the red BRAKE lamp in the instrument cluster. The low fluid level could indicate a leak, but sometimes just indicates low, worn brake linings that have caused the caliper pistons and wheel cylinders to extend further, and thus using more fluid to exert force on them. Inspect the brake system for hydraulic fluid leaks and also inspect the brake linings for excessive wear.
Retrieving the Diagnostic Trouble Codes can be accomplished by the do-it-yourselfer with the proper scan tool. Attach the TECH 1-A scan tool or equivalent into the Diagnostic Link Connector (DLC) and follow the scan tool manufacturer's instructions to retrieve the DTCs from the ABS system.
Fig. Fig. 1: Typical ABS component schematic
The Anti-lock Braking System (ABS) is standard equipment on all J-body cars covered by this guide. ABS provides the driver with 3 important benefits over standard braking systems: increased vehicle stability, improved vehicle steerability, and potentially reduced stopping distances during braking. It should be noted that although the ABS-VI system offers definite advantages, the system cannot increase brake pressure above master cylinder pressure applied by the driver and cannot apply the brakes itself.
The ABS-VI Anti-lock Braking System consists of a conventional braking system with vacuum power booster, compact master cylinder, front disc brakes, rear drum brakes and interconnecting hydraulic brake lines augmented with the ABS components. The ABS-VI system includes a hydraulic modulator assembly, Electronic Brake Control Module (EBCM) or Electronic Brake and Traction Control Module (EBTCM) (these are all different Computer Control Modules which differ depending upon vehicle year and application), a brake fluid level sensor, a system relay, 4 wheel speed sensors, interconnecting wiring and an amber ABS warning light.
The EBCM/EBTCM monitors inputs from the individual wheel speed sensors and determines when a wheel or wheels is/are about to lock up. The EBCM/EBTCM controls the motors on the hydraulic modulator assembly to reduce brake pressure to the wheel about to lock up. When the wheel regains traction, the brake pressure is increased until the wheel again approaches lock-up. The cycle repeats until either the vehicle comes to a stop, the brake pedal is released, or no wheels are about to lock up. The EBCM/EBTCM also has the ability to monitor itself and can store diagnostic codes in a non-volatile (will not be erased if the battery is disconnected) memory. The EBCM/EBTCM is serviced as an assembly.
The ABS-VI braking system employs 2 modes: base (conventional) braking and anti-lock braking. Under normal braking, the conventional part of the system stops the vehicle. When in the ABS mode, the Electromagnetic Brakes (EMB) action of the ABS system controls the two front wheels individually and the rear wheels together. If the one rear wheel is about to lock up, the hydraulic pressure to both wheels is reduced, controlling both wheels together.