Travel Sensor Operation
The SAHR Actuator assembly includes a stroke travel sensor which tells the position of the output shaft to the ECU. This is the only sensor that communicates the operational status (released or applied) of the SAHR Actuator.
The following graphic shows a steel slug inside the aluminum tube which makes up the main component of the output shaft. The travel sensor contains a magnet and a Hall effect switch. When the steel slug passes close to the sensor, it conducts the magnetic field of the magnet inside the sensor and thus changes the state of the Hall effect switch.
Travel Sensor Diagnosis
Only move on to travel sensor diagnosis after verifying that the SAHR unit strokes within the correct range, refer to Check The SAHR Actuator For Proper Operation.
This procedure requires the use of a DC power supply or battery capable of supplying 12 -14 volts DC to power the Travel Sensor.
- Refer to the following graphic to connect the power supply as follows:
• Power Supply Positive (+) connects to Travel Sensor
- Power Terminal A
- • Power Supply Negative(-) connects to Travel Sensor Ground Terminal B
- Use a standard voltmeter, capable of measuring 0- 14 volts DC, to measure the travel sensor output. Connect the voltmeter as follows:
• Volt Meter Positive (+) connects to Travel Sensor
- Signal Output Terminal C
- • Volt Meter Negative (-) connects to Travel Sensor Ground Terminal B
- Connect a 1.2k ohm resistor between the Travel Sensor power terminal A and Travel Sensor Output terminal C.
When the SAHR Actuator is fully released, the metal slug will not be under the Travel Sensor. Thus, the reading on the volt meter should be the same as the power supply, approximately 12-14V DC.
When the SAHR Actuator is applied, the steel slug will be under the Travel Sensor. This will change the state of the switch. The output voltage should drop to less than 1 volt.
When the SAHR Actuator is released again, the reading on the volt meter should return to the higher level: that is, it should be the same as the power supply, approximately 12-14V DC.
Looking at the end of the travel sensor connector there are 3 pins
The system ECU supplies power between 9 -18 volts to the Travel Sensor.
When the steel slug is not under the Travel Sensor, the output signal should be the same voltage as the sensor input voltage.
When the steel slug is under the sensor, the output signal should be less than 1 volt.
For the following steps, be sure to use wheel chocks so that the vehicle will not roll.
Check The SAHR Actuator For Proper Operation
After placing wheel chocks to prevent the vehicle from rolling, release the parking brake by:
• Turn key to the ignition position; this provides power to the brake system.
• Press down on the brake pedal to apply the service brakes.
• Push dash switch to release the parking brake.
When the brake is released, the output shaft extends out of the SAHR Actuator housing and stops at a set distance. This set distance is controlled by internal mechanical stops. With the brake released, a tape measure can be used to measure from the jam nut on the end of the output shaft to the seam in the SAHR Actuator housing.
When the brake is released, the parking brake cable should be slack.
When the brake is applied, the parking brake cable will be under tension. If the stroke is outside of the preferred operating range per Fig above, inspect and adjust the appropriate mechanical parts of the brake system to bring the stroke back within that range.
If the SAHR Actuator reaches the over-stroked position, it is an indication that one of the other system components may be damaged or misadjusted. Over- stroke is not a failure of the SAHR, but an indication that something else is not correct.
Part discussed in this article: