6E1-48 DRIVEABILITY AND EMISSIONS
Reading Flash Diagnostic Trouble Codes
The provision for communicating with the Engine
Control Module (ECM) is the Data Link Connector
(DLC). The DLC is located behind the lower front
instrument panel. It is used in the assembly plant to
receive information in checking that the engine is
operating properly before it leaves the plant.
The diagnostic trouble code(s) (DTCs) stored in the
ECM’s memory can be read either through a hand-
held diagnostic scanner plugged into the DLC or by
counting the number of flashes of the ”Check Engine”
Malfunction lndicator Lamp (MIL) when the diagnostic
test terminal of the DLC is grounded. The DLC
terminal ”6” (diagnostic request) is pulled ”Low”
(grounded) by jumpering to DLC terminal ”5”, Which is
a ground wire.
This will signal the ECM that you want to ”flash”
DTC(s), if any are present. Once terminals ”5” and ”6”
have been connected, the ignition switch must be
moved to the ”ON” position, with the engine not
running. At this point, the ”Check Engine” MIL should
flash DTC12 three times consecutively.
This would be the following flash, sequence: ”flash,
pause, flash-flash, long pause, flash, pause, flash-
flash, long pause, flash, pause, flash-flash”. DTC12
indicates that the ECM’s diagnostic system is
operating. If DTC12 is not indicated, a problem is
present within the diagnostic system itself, and should
be addressed by consulting the appropriate diagnostic
chart in DRIVEABILITY AND EMISSIONS.
Following the output of DTC12, the ”Check Engine”
MIL will indicate a DTC three times if a DTC is
present, or it will simply continue to output DTC12. If
more than one DTC three has been stored in the
ECM’s memory, the DTC(s) will be output from the
lowest to the highest, with each DTC being displayed
three times.
Reading Diagnostic Trouble Codes Using
a TECH 2
The procedure for reading diagnostic trouble code(s)
is to used a diagnostic Tech 2. When reading DTC(s),
follow instructions supplied by Tech 2 manufacturer.
Clearing Diagnostic Trouble Codes
IMPORTANT: Do not clear DTCs unless directed to
do so by the service information provided for each
diagnostic procedure.
If the fault that caused the DTC to be stored into
memory has been corrected, the Diagnostic Executive
will begin to count the ”warm-up” cycles with no further
faults detected, the DTC will automatically be cleared
from the ECM memory.
To clear Diagnostic Trouble Codes (DTCs), use the
Tech 2 ”clear DTCs” or ”clear information” function.
When clearing DTCs follow instructions supplied by
the Tech 2 manufacturer.
When a Tech 2 is not available, DTCs can also be
cleared by disconnecting one of the following sources
for at least thirty (30) seconds.
NOTE: To prevent system damage, the ignition key
must be ”OFF” when disconnecting or reconnecting
battery power.
• The power source to the control module. Examples:
fuse, pigtail at battery ECM connectors etc.
• The negative battery cable. (Disconnecting the
negative battery cable will result in the loss of other
on-board memory data, such as preset radio
tuning).
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