DIAGNOSTICS
SERVICE MANUAL NUMBER 24
Page 5G-28
90-861327--1 OCTOBER 1999
Chart A-2 (1 of 2): MIL ON Steady - Will Not Flash DTC 12
TO ECM 15A
BATTERY
FUSE
451 WHT/BLK
DLC
CONNECTOR
IGN, INJECTOR KS
MODULE 10 AMP
FUSE
461 ORN/BLK or ORN
450 BLK/WHT or BLK
(BLK/WHT - Some Models)
ECM
MEFI 1
MEFI 2
J1-18
J1-14
J1-30
J1-7
MEFI 3
J1-32
J1-4
J2-31
J1-11
J1-32
J1-16
J1-9
J2-32
J2-1
J2-22
J1-20
450 BLK/WHT or BLK
450 BLK/WHT or BLK
439 PNK/BLK or PNK
450 BLK/WHT or BLK
J1-5
TO ECM 15A
BATTERY
FUSE
CIRCUIT DESCRIPTION:
When the CodeMate Tester is installed, it plugs into the DLC terminals “F” and “E.” It
receives voltage through CKT 440 terminal “F.” Terminal “E” is ground through CKT 419 from
the ECM. There should always be a steady MIL with the ignition ON and the engine stopped.
The Engine Control Module (ECM) turns the MIL ON by grounding the MIL driver circuit.
When the diagnostic tests terminal on the DLC is grounded by jumping terminal “B” to termi-
nal “A,” the ground circuit is completed. The MIL will flash a DTC 12 followed by any DTC
stored in memory. A steady light suggests CKT 419 is shorted to ground or an open in CKT
451 from the ECM to the DLC.
DIAGNOSTIC AIDS:
An intermittent may be caused by a poor connection, rubbed through wire insulation or a
wire broken inside the insulation. Check for the following items:
•
Poor connection or damaged harness. Inspect the ECM harness and connectors for
improper mating, broken locks, improperly formed or damaged terminals, poor termi-
nal to wire connection and damaged harness.
If the engine runs OK, check for a faulty light bulb or an open in the MIL driver circuit (CKT
419). If the engine cranks but will not run, check for an open ECM ignition or battery feed
or a poor ECM to engine ground.
Index