Isuzu 4HL1, Workshop Manual

Page: 40 / 267

1A-38 Engine Control System
12-Way Connector
22-Way Connector
Strategy-Based Diagnostics
Strategy-Based System Diagnostics
The system diagnostic is a uniform approach to repair
all electrical/electronic (E/E) systems. In the E/E
system, different from general vehicle problems, faults
frequently occur along the steps shown as follows.
1. Initial stage:
• A single fault occurs for a short while and,
therefore, the customer may miss it. In this
stage, the customer complaint is unclear and
the fault cannot be reproduced. But, the ECM
may have stored the fault.
= Past fault
2. Middle stage:
• A single fault occurs for a short while but is
observed intermittently. It always occurs under
certain conditions. The customer complaint
(description of fault) is clear but fault
occurrence conditions are unidentified. If you
comprehend these conditions, you can
reproduce the trouble.
= Intermittent fault (intermittent)
3. Realistic fault:
• The fault occurs certainly and the customer
complaint is realistic and clear. You can
reproduce the fault. However, there may exist
two or more causes.
= Current fault
The diagnostic flow can always be used to resolve an
E/E system problem and is a starting point when
repairs are necessary. The following steps will instruct
the technician how to proceed with a diagnosis:
1. Verify the customer complaint:
• To verify the customer complaint, the technician
should know the normal operation of the
system.
2. Perform preliminary checks:
• Conduct a thorough visual inspection.
• Review the service history.
• Detecting unusual sounds or odors.
• Gather DTC (diagnostic trouble code)
information using Tech 2
3. Check bulletins and other service information.
4. Refer to “Symptom Diagnosis Chart” in this
manual.
Pin No. Connected to Pin No. Connected to
22 — 60 Signal ground
23 — 61 —
24 DLC (Tech 2 communications) 62 —
25 — 63 —
26 ECM (CAN communications) 64 —
27 ECM (CAN communications) 65 Shield ground (CAN communications)
Pin No. Connected to Pin No. Connected to
28 — 66 VIM power ground
29 — 67 —
30 Idle up volume 68 —
31 PTO accelerator sensor signal 69 —
32 — 70 —
33 — 71 5 V sensor ground 1 (PTO, IDL UP)
34 5 V sensor power 1 (PTO, IDL UP) 72 —
35 — 73 Casing ground
36 Starter switch (ON) 74 —
37 — 75 VIM power
38 VIM power 76 VIM power