Diagnosis & Testing: Description

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NOTE: Tech 1 scan tester is recommended when testing and diagnosing 4WAL system, but is not necessary.

The Electro-Hydraulic Control Unit (EHCU) contains a self-diagnostic capability to detect system failures. When a fault code is set, the EHCU may disable 4WAL system and illuminate ANTILOCK light for duration of ignition cycle. Fault codes stored by EHCU can be displayed using on-board diagnostics or Tech 1 with appropriate cartridge.

Before diagnosing 4WAL system, perform a comprehensive visual inspection of system by checking wiring harness connectors for looseness and harness routing (pay particular attention to wheel speed sensor wiring harness routing), applicable fuses in fuse block and ground connections. Ensure brake fluid level in master cylinder reservoir is full.

Start 4WAL system diagnosis with DIAGNOSTIC CIRCUIT CHECK chart under TROUBLE SHOOTING CHARTS . See Figure. If failures are found during DIAGNOSTIC CIRCUIT CHECK, you will be directed to enter diagnostics to retrieve codes, perform symptom diagnosis or diagnose brake system warning light. DIAGNOSTIC CIRCUIT CHECK may indicate 4WAL system is functioning properly.