ABS - System Pressure Checks Using Gauge
Bulletin: P91-005Section: PRODUCT
Dated: 02/22/91
Applicable to: USA, Canada
SUBJECT:
ABS PRESSURE GAUGE - USE INSTRUCTIONS
The ABS pressure gauge is an important diagnostic tool for lasting problems in the ABS power assist circuit.
The following pages outline steps for using the gauge and interpreting readings. They include:
- Gauge installation
- System operation information
- Gauge removal
- System specifications
WARNING:
The ABS system contains brake fluid under very high pressure. Follow instructions for de-pressurizing system before installing or removing gauge. Brake fluid is flammable and destroys paint finish rapidly. Prevent contact with eyes and skin with appropriate safety precautions.
GAUGE INSTALLATION
1. De-pressurize the accumulator by pumping the brake pedal at least 30 times with the ignition "OFF". The pedal will feel lower but firmer once the pressure has been fully reduced.
2. Wipe off the banjo bolt on the pump head with a clean rag before loosening.
3. Protect the paint work from brake fluid spills.
4. Switch "on" the ignition.
5. Check the banjo bolt/pump adaptor connection for leakage once installed and pressurized.
6. Repeat Step 1 before starting test.
SYSTEM OPERATION
To check normal system operation, switch "on" ignition and observe:
- Rapid pressure rise to accumulator pre-charge pressure (50-80 BAR), then...
- Slower rise as accumulator diaphragm is compressed, then...
- Pump cut-off at 170 BAR within 1 minute of starting test.
- Pump noise changes slightly as pressure rises and load increases.
Switch "off" ignition and observe:
- Very slow pressure drop from 170 to 130 BAR (approximately 5-6 minutes minimum).
Switch "on" ignition to rebuild pressure and then switch "off".
- Pump brake pedal and note pressure drop as accumulator empties - 20 to 30 pumps should be required to reduce pressure from 170 BAR to 0. The point at which the pressure quickly drops to 0 is the pre-charge value.
GAUGE REMOVAL
With system fully de-pressurized:
- Remove gauge and adaptor.
- Re-assemble fittings and check for leaks.
- Top up reservoir with DOT4 Brake Fluid from a sealed container.
ABS POWER ASSIST CIRCUIT-TEST SPECIFICATIONS