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Wrenchtech
Wrenchtech, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1403
Experience:  40 years experience with ASE certification as Master Technician with L1--Repair Shop Owner
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S10: Blazer..4x4..brake lines..we are unable to bleed the system

Resolved Question:

We have a Blazer S10 1999 4x4. After replacing the brake lines front to rear we are unable to bleed the system. We can get a hard pedal wiyj the engine off, but as soon as the engine is started the pedal goes to the floor. I'm told we need to bleed the ABS Modulator. How do I do this?
Submitted: 5 years ago.
Category: Chevy
Expert:  Wrenchtech replied 5 years ago.
Electronic bleeding requires the use of a Tech2 scan tool.

Here is some info on it.


F2 - Special Functions
In this test mode, the scan tool can be used to perform functional tests on the ABS which help verify proper operation. Malfunction conditions can be further identified by testing and observing the test results. DTCs must be cleared before any tests in Special Functions can be performed. In a vehicle equipped with ABS, the Special Functions are grouped as following:

  • Function Test
  • Automated Bleed
  • ABS Motor
  • System Identification
  • Tire Size Calibration
  • ABS Lamp
  • Solenoid Tests (for all Dump and Isolation solenoid valves)
  • ABS Relay
  • Brake Lamp

Function Test
The Function Test cycles each valve solenoid and the pump motor (as well as the necessary relays) to check component operation. If a malfunction is detected, the EBCM will set DTC(s), which will be displayed upon completion of the test. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the Function Test.
  6. Run the Function Test.
  7. Note any DTCs set. Automated Bleed Automated Bleed cycles each valve solenoid and the pump motor in a special sequence (as well as the necessary relays) in order to bleed air out of the BPMV after removal or installation of brake lines, or BPMV replacement. Perform the test as follows:
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the Automated Bleed function.
  6. Run the Automated Bleed function. ABS Motor This function tests the ABS pump motor to check component operation. If a malfunction is detected, the EBCM will set DTC(s), and the ABS indicator lamp will turn on. Perform the test as follows:
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the ABS Motor Test.
  6. Run the ABS Motor Test. System Identification This function is used to identify the hardware and software revision of the Electro-Hydraulic Control Unit (EHCU) .
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select System Identification.
  6. Make note of the relevant information. Tire Size Calibration This function allows the EBCM tire size to be set or changed when a new EBCM is installed, or different tires/wheels are installed on the vehicle.
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the Tire Size Calibration.
  6. Make the necessary changes to existing tire size setting. ABS Lamp This test allows activation of the ABS indicator. The ABS Lamp test aids in diagnosing indicator malfunctions. The test allows the operator to turn the indicator on and off manually. BRAKE Lamp This test allows activation of the BRAKE indicator. The BRAKE Lamp test aids in diagnosing indicator malfunctions. The test allows the operator to flash the indicator on and off manually. Solenoid Tests (Isolation Valves) The Solenoid Test for isolation valves activates the selected wheel circuit Isolation valve, placing it in the pressure hold position. When in the pressure hold position, the valve will not allow master cylinder pressure to be delivered to the hydraulic wheel circuit. This is done under ABS operating conditions because the EBCM has determined that the wheel is moving too slowly, so it holds additional master cylinder pressure from it in an attempt to allow it to rotate at an appropriate speed. The scan tool commands the valve to close, which should allow the technician to spin the wheel even though an assistant is applying pressure to the brake pedal. Perform the test as follows:
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Raise vehicle such that wheels are about 6 inches off the floor with the transmission in neutral.
  5. Select the scan tool's Special Functions.
  6. Select the desired Isolation Solenoid test. Have an assistant command the Isolation valve ON with the scan tool.
  7. Have the assistant press and hold the brake pedal.
  8. Attempt to move the wheel being tested by hand; it should move even though the assistant is applying pressure to the brake pedal. The wheels may be difficult to turn by hand, but can be moved if the system is working properly. Solenoid Tests (Dump Valves) The Solenoid Test for Dump valves activates the selected hydraulic wheel circuit Dump valve, placing it in the pressure release position. When in the pressure release position, the valve will allow wheel caliper pressure to be returned to the master cylinder circuit. This is done under ABS operating conditions because the EBCM has determined that the wheel is moving too slowly, and holding additional master cylinder pressure from it has not allowed it to rotate at an appropriate speed. The scan tool commands the valve to release hydraulic pressure to the affected brake caliper, which should allow the technician to spin the wheel even though an assistant is applying pressure to the brake pedal. Perform the test as follows:
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Raise vehicle such that wheels are about 6 inches off the floor with the transmission in neutral.
  5. Have an assistant press and hold the brake pedal.
  6. Select the scan tools Special Functions.
  7. Select the desired Dump Solenoid Test. Have the assistant command the Dump valve ON with the scan tool.
  8. Attempt to move the wheel being tested by hand; it should move even though the assistant is applying pressure to the brake pedal. The wheels may be difficult to turn by hand, but can be moved if the system is working properly. ABS Relay This function tests the ABS relay to check component operation. If a malfunction is detected, the EBCM will set DTC(s), and the ABS indicator lamp will turn on. Perform the test as follows:
  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the ABS Relay.
  6. Take note of the relay status as the relay is cycled. F3 - Snapshot In this test mode, the scan tool captures the data listed in the data displays before and after a snapshot. The following triggering conditions are available:
    • DTC-In this mode, the snapshot will be triggered on a specific (operator selected) DTC.
    • Any DTC in this mode, the snapshot will trigger on any DTC
    • Auto Trigger-will trigger a snapshot under two conditions:
  1. Wheel speed out of range-Snapshot will trigger when a WSS/VSS input is ±11 km/in (7 mph) out of range in relation to other WSS/VSS inputs.
  2. ABS Stop-Snapshot will trigger when an ABS event occurs.



Here are the instructions for manual bleeding.



Two Person Procedure

Important:

  • Use the two-person bleed procedure under the following conditions:
  • Installing a new Electro-Hydraulic Control Unit (EHCU) or new Brake Pressure Modulator Valve(BPMV).
  • Air is trapped in the valve body
  • Do not drive the vehicle until the brake pedal feels firm.
  • Do not reuse brake fluid that is used during bleeding.
  • Use the vacuum, the pressure and the gravity bleeding procedures only for base brake bleeding.
  1. Raise the vehicle in order to access the system bleed screws.
  2. Bleed the system at the right rear wheel first.
  3. Install a clear hose on the bleed screw.
  4. Immerse the opposite end of the hose into a container partially filled with clean DOT 3 brake fluid.
  5. Open the bleed screw 1/2 to one full turn.
  6. Slowly depress the brake pedal. While the pedal is depressed to its full extent, tighten the bleed screw.
  7. Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.
  8. Repeat the previous steps for the remaining wheels. The brake fluid which is present at each bleed screw should be clean and free of air.
  9. This procedure may use more than a pint of fluid per wheel. Check the master cylinder fluid level every four to six strokes of the brake pedal in order to avoid running the system dry.
  10. Press the brake pedal firmly and run the Scan Tool Automated Bleed Procedure. Release the brake pedal between each test.
  11. Bleed all four wheels again using Steps 3-9. This will remove the remaining air from the brake system.
  12. Evaluate the feel of the brake pedal before attempting to drive the vehicle.
  13. Bleed the system as many times as necessary in order to obtain the appropriate feel of the pedal.

 

Customer: replied 5 years ago.

Thanks for that.

 

Unfortunately I do not have a TECH2 scan tool (v. expensive) is there another tool such as Snap On that can do the ABS Automated Bleed Procedure?

Expert:  Wrenchtech replied 5 years ago.
It's the software that determines that.

I believe some of the most recent updates will enable the snap-on to do this. You really have to check the data pertaining to the software. Sometimes they are selective in doing some models and not others.
Wrenchtech, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1403
Experience: 40 years experience with ASE certification as Master Technician with L1--Repair Shop Owner
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