Primary Press/Delta Pressure Fault (Non-Latching)

PRIMARY PRESS/DELTA PRESSURE FAULT (NON-LATCHING)

WARNING LIGHTS
BRAKE and ANTILOCK during a brake application.

DETECTION
This fault is detected anytime with brake applied.

DESCRIPTION
This is a fault in the base hydraulic braking system.

The primary pressure transducer senses master cylinder primary pressure and converts it to a voltage on a 0.25 - 5.0 volt linear scale; i.e., 0.25 volts equals 0 psi, and 5 volts equals 2500 psi.

This voltage is compared to the output of the boost pressure transducer to determine proper operation.
- Boost pressure and primary pressure should always be approximately equal.
- However, boost pressure typically will be higher by a few hundredths of a volt due to friction losses in the piston seals in the master cylinder.
- If boost pressure is below 300 psi of primary pressure, the BOOST PRESSURE fault is set.

In addition, the differential pressure switch (Delta P switch) is used to detect a differential pressure of greater than 300 psi between the primary and secondary master cylinder circuits. If detected, the Delta P switch grounds the output of the primary pressure transducer, resulting in a 0.0 volt input to the CAB.