ELECTRICAL SYSTEM CONTINUED
Brake Backup Pole
The brake backup pole of the parking brake switch operates independently of the ECM. The pole is a backup to the
ECM and the ON/OFF pole of the parking brake switch. Normally, the ECM applies the left brake according to the
status of the ON/OFF pole. The brake backup pole ensures that the brake is engaged if either the ON/OFF pole or
the ECM is not functioning properly.
When the parking brake switch is in the ON position, the brake backup pole sends a +battery signal to the parking
brake solenoid. The parking brake solenoid engages the left brake. The fuse for the ECM is the source of the
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The parking brake solenoid is also connected to the ECM. The ECM will send +battery
voltage to the parking brake solenoid if the signal for the brake backup pole is not at
+battery voltage and the parking brake switch is in the ON position.
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The ON/OFF pole diagnoses an INCORRECT condition of the brake backup pole. The
ECM monitors the status of the ON/OFF pole and the output for the parking brake
solenoid. The ON/OFF pole tells the ECM whether the parking brake switch is in the ON or
Figure 7. Mechanical Parking Brake Switch Actuator.