I did find 1 complaint.
|Make: ||CHEVROLET |
|Model: ||CHEVROLET TRUCK |
|Year: ||1995 |
|Complaint Number: ||517777 |
|BRAKES FAIL TO IMMEDIATELY RESPOND WHEN BRAKE PEDAL IS DEPRESSED, RESULTING IN EXTENDED STOPPING DISTANCE. |
|Make : CHEVROLET||Model : CHEVROLET TRUCK||Year : 1995|
|Manufacturer : GENERAL MOTORS CORP.|| |
|Crash : No||Fire : No||Number of Injuries: 0|
|ODI ID Number : 517777||Number of Deaths: 0|
|Date of Failure: |
|VIN : 2GCFC29K851...|| |
|Component: SERVICE BRAKES, HYDRAULIC:ANTILOCK|
Is there any fault codes?
Rear Wheel Anti-lock Rwal Brake System
See Figures 1 and 2
Fig. Fig. 1: Rear wheel anti-lock brake system schematic-R/V Series
Fig. Fig. 2: Rear wheel anti-lock brake system schematic-C/K Series
The Kelsey Hayes RWAL system is found on Chevrolet and GMC products including Suburban and C/K Series pick-ups. The system is particularly useful because of the wide variations of loading the vehicle may experience. Preventing rear wheel lock-up often makes the difference in controlling the vehicle during hard or sudden stops.
Found on both 2WD and 4WD vehicles, the RWAL system is designed to regulate rear hydraulic brake line pressure, preventing wheel lock-up at the rear. Pressure regulation is managed by the control valve, located under the master cylinder. The control valve is capable of holding, increasing or decreasing brake line pressure based on electrical commands from the RWAL Electronic Control Unit (ECU) or Electronic Brake Control Module (EBCM).
The RWAL ECU is a separate and dedicated microcomputer mounted next to the master cylinder; it is not to be confused with the engine management ECU. The RWAL ECU receives signals from the speed sensor. The speed sensor sends its signals to the Vehicle Speed Sensor buffer (previously known as the Digital Ratio Adapter Controller or DRAC) within the instrument cluster. The buffer translates the sensor signal into a form usable by the ECU. The RWAL ECU reads this signal and commands the control valve to function. If commanded to release pressure, the dump valve releases pressurized fluid into the accumulator where it is held under pressure. If a pressure increase is called for, the isolator valve within the control valve pulses, releasing pressurized fluid into the system.
The RWAL system is connected to the BRAKE warning lamp on the instrument cluster. A RWAL self-check and a bulb test are performed every time the ignition switch is turned to ON . The BRAKE warning lamp should illuminate for about 2 seconds and then go off. Problems within the RWAL system will be indicated by the BRAKE warning lamp staying illuminated.
If a fault is detected within the system, the RWAL ECU will assign a fault code and store the code in memory. The code may be read to aid in diagnosis.
System Diagnosis and Testing
See Figures 1 through 7
Fig. Fig. 1: Diagnostic circuit check-rear wheel anti-lock brake system
Fig. Fig. 2: Diagnostic test-brake light is ON
Fig. Fig. 3: Diagnostic test-brake light is ON
Fig. Fig. 4: Diagnostic test-brake light is ON
Fig. Fig. 5: Diagnostic test-brake light is intermittent
Fig. Fig. 6: Diagnostic test-brake light is flashing
Fig. Fig. 7: Diagnostic test-brake light is OFF
If the vehicle is equipped with air bag (SIR) system, always properly disable the system before commencing work on the ABS system. Certain components within the RWAL system are not intended to be serviced or repaired. Only those components with removal & Installation procedures should be serviced. Do not use rubber hoses or other parts not specifically specified for the RWAL system. When using repair kits, replace all parts included in the kit. Partial or incorrect repair may lead to functional problems. Lubricate rubber parts with clean, fresh brake fluid to ease assembly. Do not use lubricated shop air to clean parts; damage to rubber components may result. Use only brake fluid from an unopened container. Use of suspect or contaminated brake fluid can reduce system performance and/or durability. A clean repair area is essential. Perform repairs after components have been thoroughly cleaned; use only denatured alcohol to clean components. Do not allow components to come into contact with any substance containing mineral oil; this includes used shop rags. The RWAL ECU is a microprocessor similar to other computer units in the vehicle. Insure that the ignition switch is OFF before removing or installing controller harnesses. Avoid static electricity discharge at or near the controller. Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test. Always wear a grounded wrist strap when servicing any control module or component labeled with a Electrostatic Discharge (ESD) symbol. Avoid touching module connector pins. Leave new components and modules in the shipping package until ready to install them. To avoid static discharge, always touch a vehicle ground after sliding across a vehicle seat or walking across carpeted or vinyl floors. Never allow welding cables to lie on, near or across any vehicle electrical wiring. Do not allow extension cords for power tools or droplights to lie on, near or across any vehicle electrical wiring.
Before reading trouble codes, perform the Diagnostic Circuit Check according to the chart. This test will aid in separating RWAL system problems from common problems in the hydraulic brake system. The diagnostic circuit check will direct the reading of trouble codes as necessary.
The RWAL ECU will assign a code to the first fault found in the system. If there is more than 1 fault, only the first recognized code will the stored and transmitted.
Trouble codes may be read either though the use of TECH-1 or equivalent scan tool or by connecting a jumper wire from pin H on the ALDL to pin A. If the jumper method is used, the fault code will be displayed through the flashing of the BRAKE warning lamp on the dash. The terminals must be connected for about 20 seconds before the display begins. The display will begin with 1 long flash followed by shorter ones-count the long flash as part of the display.
Sometimes the first display sequence will be inaccurate or short; subsequent displays will be accurate.
If using a hand scanner, note that if a soft code is stored, only the last recognized code will be retained and displayed on the scanner. Soft fault codes 6, 9 and 10 can only be read with a scan tool. Codes 1, 11 and 12 will not read on the scan tool; they must be read using the jumper wire method.
Never ground terminal H of the ALDL to terminal A if the BRAKE warning lamp is not lit. Doing so will set a false code 9 and illuminate the BRAKE warning lamp. With the brake lamp on, the RWAL system will be disabled.
Stored trouble codes must be cleared with the ignition switch OFF . Remove the STOP/HAZARD fuse for at least 5 seconds, the reinstall the fuse.
Four Wheel Anti-lock Brake System
Vehicle Speed Sensor
Prefer to of this repair guide for VSS testing.
Wheel Speed Sensor
See Figure 1
- Elevate and safely support the vehicle.
- Unplug the sensor electrical connection.
- Check the condition of the sensor terminals and the wiring harness terminals. Repair as necessary.
- Check the sensor wiring harness for an open or short circuit. Repair as necessary.
- Using a Digital Volt OhmMeter (DVOM) set to read resistance, probe the sensor terminals.
- If the resistance is not as specified in the accompanying charts, the sensor may be defective.
- Turn the DVOM to the A/C voltage scale and spin the wheel, there should be a voltage reading. As the wheel speed increases, the voltage should increase. If there is no voltage present, or the voltage does not increase with wheel speed, check the tone wheel for defects. If the tone wheel is found to be in good condition, replace the sensor.
Fig. Fig. 1: Wheel speed sensor temperature versus resistance chart
Pump motor circuit
- Check the condition of the fuse in the relay center and replace as necessary.
- Unplug the pump motor electrical connection.
- Check the condition of the terminals and the wiring harness terminals. Repair as necessary.
- Attach the electrical connection.
- Using a Digital Volt OhmMeter (DVOM) set to read voltage, backprobe between the black (ground) wire and red (power) wire terminals of the harness . The voltage should be between 9-14 volts.
- If the voltage is less than 9 volts, set the DVOM on the lowest resistance scale, disconnect the harness and the positive and negative battery terminals. Connect one probe to the positive battery cable and the other probe to red wire terminal. Note the reading. Connect one probe to the negative battery cable and the other probe to black wire terminal. Note the reading.
- If the resistance is less than one ohm the wiring is fine and the control unit should be replaced.
- If the resistance is more than one ohm, clean and tighten the terminals or repair the wiring as needed.
- Attach all unplugged wires and recheck the voltage.
- Clear the trouble codes and road test the vehicle. If the trouble code returns, check the motor supply voltage again.
- If the voltage is now between 9-14 volts and the pump is still not functioning properly, replace the assembly.
- If the voltage is still lower than 9 volts, there may be a problem with the EBCM.
See Figures 1 and 2
Fig. Fig. 1: Functional test-2WD models
Fig. Fig. 2: Functional test-4WD models
System diagnosis begins with the diagnostic circuit check as given in the chart. If the chart is used correctly, it will aid in elimination of simple, non-system problems such as blown fuses of failed bulbs. The chart will prompt the reading of codes at the proper point in the diagnosis.
Some of the diagnostic or repair procedures refer to the performance of a Function Test. This test is performed with the scan tool; it operates all components of the EHCU valve and checks their function. The test cannot be performed without the scan tool.
Stored trouble codes are transmitted through the flashing of the amber ANTI-LOCK dash warning lamp. The system may be put into diagnostic mode with a jumper wire, however, the use of the TECH-1 scan tool or its equivalent is highly recommended. The scan tool will allow performance of the specific system tests called for by the trouble tree for each code.
On all models except 1996-98, the codes can be read without the use of a hand scanner. To read the codes, use a jumper wire to connect terminal H on the ALDL to either body ground or to terminal A. The terminals must be connected for a few seconds before the code(s) will transmit. Observe the ANTI-LOCK light on the dash and count the flashes in groups: a group of 4 flashes, a pause and a group of 3 flashes indicates Code 43. Codes 12 and 14 are not trouble codes, but may appear with them to indicate normal operation. Not all vehicles use Code 12 or 14.
After the trouble codes have been read, refer to the correct trouble tree for each code. After repairs, repeat the initial diagnostic circuit check to confirm normal operation of the system.
Stored codes may be erased with the hand scanner if available. If not using a hand scanner, codes may be cleared as follows:
- Turn the ignition switch ON but do not start the engine.
- Use a jumper wire to ground ALDL terminal H to terminal A for 2 seconds.
- Remove the jumper wire for 2 seconds.
- Repeat the grounding and un-grounding two more times. Each connection and opening of the circuit should last 2 seconds.
- Connect the jumper to terminals H and A for a longer time; no trouble codes should be displayed. If codes are displayed, the system was not properly erased.
- If no trouble codes appear, the memory has been cleared. Turn the ignition switch OFF .