DRIVEABILITY AND EMISSIONS 6E1-55
ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
16 15 14 13 12 11 10 9
87654321
HOT AT ALL TIMES
Fuse
Stop
10A
U/H
FUSE
BLOCK
To
Stop
Lamp
Engine
Control
Module
(ECM)
0.5G
A1 B11 E8
B/R 0.5
BW
0.5
R
ECM
Grounds
(Engine Block)
Diag Serial Data
1.25
Circuit Description
The on-board diagnostic system check is the starting
point for any driveability complaint diagnosis. Before
using this procedure, perform a careful visual/physical
check of the ECM and engine grounds for cleanliness
and tightness.
The on-board diagnostic system check is an organized
approach to identifying a problem created by an
electronic engine control system malfunction.
Diagnostic Aids
An intermittent may be caused by a poor connection,
rubbed-through wire insulation or a wire broken inside
the insulation. Check for poor connections or a
damaged harness. Inspect the ECM harness and
connectors for improper mating, broken locks,
improperly formed or damaged terminals, poor
terminal-to-wire connection, and damaged harness.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart:
1. The MIL (“Check Engine” lamp) should be ON
steady with the ignition ON/engine OFF. If not,
isolate the malfunction in the MIL circuit.
2. Checks the serial data circuit and ensures that the
ECM is able to transmit serial data.
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