Unblinking Check Engine Lamp Check - Isuzu 4HL1 Workshop Manual

1A-54 Engine Control System

Unblinking CHECK ENGINE Lamp Check

Circuit Description
After DLC pins are shorted (i.e., the diagnostic switch is
turned on), the CHECK ENGINE lamp starts blinking to
indicate the engine and related systems are in faulty or
normal condition.
The ECM recognizes the ON signal from the diagnostic
switch and blinks the CHECK ENGINE lamp.
Diagnostic Aids
An intermittent may be caused by a poor connection, a
rubbed-through wire insulation, or a wire broken inside
the insulator. Check for the following conditions and, if
a fault is found, perform repair or replacement.
• Poor connection
connectors for backed-out pins, improper mating,
broken locks, improperly formed or damaged pins,
and poor pin-to-wire connection.
Battery
0.5B
Main
DLC
Relay
112 88 118 117 116 115 114
at ECM: Inspect
SBF SBF
100A 50A
3W/L
SBF
50A
SBF SBF
30A 60A
Glow
Relay
Glow
Relay
121 120 119
• Damaged harness: Inspect the wiring harness for
rubbed-through wire insulation or wire broken
inside the insulator.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2: When even disconnecting the ECM does not turn off
the CHECK ENGINE lamp, the ground circuit of the
lamp is shorted.
harness
IG IG
(ST) (ON)
#22 #19
10A 15A
CHECK
ENGINE
Lamp
113 109 99
ECM
(Engine
Control
Module)
95 87
LNW21ALF006001-X