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DIAGNOSTIC INTRODUCTION
On-Board Diagnostic (OBD) System Check
The basic steps of any diagnosis are as follows:
1. Observe the Malfunction Indicator Lamp (MIL) with
engine running. If MIL is illuminated, then current
Diagnostic Trouble Codes (DTCs) are present.
2. Read DTC(s) using MIL, Tiny Scan Code Reader,
or Diagnostic Tool software.
3. To diagnose system problem(s), proceed to the
applicable Diagnostic Table(s) in
SECTION 2 -
TROUBLESHOOTING DTCs
.
4. Once the problem is located and corrected through
repair or replacement of faulty components, clear
DTC(s) using the Tiny Scan Code Reader or
the Diagnostic Tool software.
NOTE:
For information on the location or
replacement of specific components, see
SECTION 5
- REMOVAL/INSTALLATION
.
5. Start and run engine to validate repairs. Observe MIL
to verify that no DTCs are set.
6. If no DTCs are set, but engine performance issues
exist, see
SECTION 4 - SYMPTOMS
.
Diagnostic Trouble Codes (DTCs)
The ECM receives voltage signals from as many as five
sensors. Each sensor functions within an established
set of parameters, which can be viewed as its operating
“window.”
When a malfunction or fault condition occurs, a change
in the signal voltage alerts the ECM that the sensor is
functioning outside its operating “window,” a DTC is set
and stored in ECM memory, and the MIL is illuminated.
A default value temporarily replaces the erroneous sensor
value to restore engine performance until the problem is
corrected.
Malfunction Indicator Lamp (MIL)
As a bulb and diagnostic system check, the MIL
illuminates at Ignition ON, Engine OFF. When the engine
is started, the MIL is extinguished if no current fault
condition exists.
If the MIL remains illuminated, it is an indication that a
current DTC is stored. If the fault should correct itself, as
in an intermittent condition, the MIL is extinguished after
a ten second delay. The DTC remains stored in ECM
memory as a historic code until cleared by the technician.
The MIL does not indicate the existence of only historic
codes.
Data Link Connector (DLC)
The DLC provides for direct communication with the
ECM. By plugging the Tiny Scan Code Reader, or laptop
with Diagnostic Tool, into the 6-pin connector in the EFI
wire harness, the DTCs stored in ECM memory can be
read and cleared.
Non-Scan Diagnostics
In the Non-Scan diagnostic mode, either the MIL or
the Tiny Scan Code Reader is used to read DTCs. The
technician then refers to the applicable Diagnostic Table
to troubleshoot the problem. Those tables labeled
Non-
Scan Diagnostics
must be used, as the data stream
provided by the ECM is not available for analysis.
Scan Diagnostics
In the more sophisticated diagnostic mode, the Diagnostic
Tool software can facilitate the diagnosis of system
problems through an expanded interface with the ECM.
Through the use of data displays and menu selections,
the technician has access to “live” data for analysis.
It is important to note that the software is not a stand-
alone diagnostic tool for resolving DTCs, but must be
used in conjunction with the Diagnostic Tables for the
most efficient and effective diagnosis. Those tables that
are applicable to users with access to the Diagnostic
Tool software are labeled as
Scan Diagnostics
.
Use MIL to Read DTCs
1. Verify that battery voltage is above 12v.
2. Turn Ignition key OFF for ten seconds.
3. Turn Ignition key ON-OFF-ON-OFF-ON (but do not
start the engine).
NOTE:
No more than 2.5 seconds can elapse
between each ON and OFF cycle or the routine is
aborted.
4. When performed correctly, the MIL begins to flash the
first of four digits.
NOTE:
While each DTC actually begins with the
letter “P,” only the numeric characters are flashed.
5. Count the number of flashes to obtain the first of four
digits. If the first digit is zero, it is represented as a
series of ten flashes.
Not for
Reproduction
Summary of Contents for VANGUARD M490000
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Page 84: ...3 80 MODEL 490000 EFI ELECTRICAL SCHEMATIC PAGE 1 OF 2 N o t f o r R e p r o d u c t i o n ...
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Page 95: ...3 91 MODELS 490000 540000 610000 FUSE RELAY BLOCK N o t f o r R e p r o d u c t i o n ...
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