MSARB Diagnostic Troubleshooting Guide - Valve Fault V5 (LED & LCD)

1. Fault Overview

When the MSB Fault Light remains constantly illuminated when the ignition is turned ON, and:

LED Displays only the ‘P’ and ‘A’ LEDs flashing alongside a beep every 30 seconds from the LED module’s buzzer.

OR

When the LCD screen logs a Valve fault,

The fault conditions will be one of below:

Conditions for setting fault

• Short/open circuit Solenoid valve coil.
• Short/open circuit wiring harness
• Internal MSB ECU fault

NOTE: Prior to performing the below diagnostic process, ensure that the vehicle’s air system, particularly the park brake system, is operational and operating within the OEM prescribed specifications. Ensure that the electrical connections within the valve circuit are in good condition, and securely attached.

NOTE: On vehicles with 2 valve assemblies, both valves MUST be inspected independently.

NOTE: The MSB ECU monitors both supply and return to the Solenoid. For under/over current faults. Do not modify or substitute valve/wiring.

2. Diagnostic Procedure

STEP 1:        Clear the fault by isolating the vehicle power supply at the batteries for at least 1 second, reconnect the power supply to the vehicle.

Locate and inspect the valve coil wiring and connectors. 

Perform a complete visual inspection of the valve circuit harness, checking for any potential wiring rub-throughs or breaks as the wire runs from the valve to the MAX-SAFE ECU. Inspect for any water ingress at the valve electrical connector. Pay close attention to the location where the wiring harness passes into the vehicle cabin.

Within specifications: Continue to STEP 2

Not within specifications: Repair/replace wiring harness as required.

STEP 2:        Disconnect valve coil. Using a multi-meter verify valve coil resistances as per Table 1.

Within specifications: Continue to STEP 3.

Not within specifications: Replace solenoid valve.

Verify repair with Full System Test.

Table 1.

STEP 3:    Locate the MSB ECU. Disconnect the Black connector (12-Way) at the ECU. Locate the white/black wire (Pin 1) and white wire (Pin 2). Perform a continuity test of the harness to the valve solenoid coil.

Within specifications: Continue to STEP 4.

Not within specifications: Repair/replace wiring harness.

Verify repair with Full System Test.

STEP 4        Reconnect MSB and valve solenoid coil.

                    Clear the fault by isolating the vehicle power supply at the batteries for at least 1 second. Reconnect the power supply to the vehicle.

Perform a Full System Test.

If the fault still appears: The ECU has failed. This scenario is unlikely: repeat all testing again to ensure that it is the ECU that has failed. If all testing has been repeated and testing still indicates that the ECU has failed, replace the ECU. 

Verify repair with Full System Test.

3. Full System Test