When troubleshooting the brake line switch circuit, make sure the brake pressure switch is identified. The vehicle brake light pressure switch, which is not a part of the Signature system, is commonly mistaken for the brake line switch used in the Signature system.
The brake pedal position switch detects the position of the service brake pedal. Certain features such as cruise control and PTO respond to the state of the brake pedal position switch and disengage when the brakes are applied. The circuit has a normally-closed switch, switch return wire, and brake pedal position switch signal wire of the OEM harness. The brake pedal position switch is mounted in the low pressure side of the vehicle pneumatic brake system. When the vehicle brakes are applied, the normally-closed switch opens and disables the cruise control operation.
Connect the probes of the multimeter to the brake pedal position switch terminals.
Measure the resistance.
The multimeter must show a closed circuit (10 ohms or less) when the brakes are not applied. If the circuit is not closed, replace the brake pedal position switch.
The vehicle must have enough air pressure to activate the brakes.
Depress the vehicle brake pedal. The multimeter must show an open circuit (100k ohms or more) when the brakes are applied. If the circuit is not open, replace the brake pedal position switch.
If the resistance value is correct, the switch must still be checked for a short circuit to ground.
Touch one multimeter probe to one of the brake pedal position switch terminals. Touch the other multimeter probe to chassis ground. Measure the resistance. The multimeter must show an open circuit (100k ohms or more) when the brake pedal is released. If the circuit is not open, replace the brake pedal position switch.
If the brake pedal position switch passed all the previous checks, connect the switch to the wiring harness. The brake pedal position switch circuit must still be checked.
Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.
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