SERVICE MANUAL NUMBER 23
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
Page 5F-16
90-861326--1 MARCH 1999
Code 42 (3 of 3): Ignition Control (IC) Circuit (Non-Scan) (Continued)
1. Ignition OFF.
2 Di
t ECM J1
d J2
t
2. Disconnect ECM J1 and J2 connectors.
3 Ignition ON
3
3. Ignition ON.
4. Use DVOM with selector in the OHMS
–
Step 4
Step 5
3
U
O
O
S
range.
5 P b ECM h
t
CKT 423
–
Ste 4
Ste 5
5. Probe ECM harness connector CKT 423
with DVOM to ground.
t
O
to g ou d
It should read more than 3000 Ohms.
Does it?
4
Probe ECM harness connector CKT 424 with a
test light connected to battery positive (B+).
–
Step 13
Step 6
4
test light connected to battery ositive (B+).
Is test light on?
–
Ste 13
Ste 6
5
Open CKT 423, faulty connection or faulty igni-
tion module.
–
–
–
6
With Ohmmeter connected to ECM harness
CKT 423 and ground (–), probe harness CKT
424 with test light connected to battery positive
(B+).
–
Step 8
Step 7
6
(B+).
As test light contacts CKT 424, resistance
should change from over 3000 Ohms to under
1000 Ohms.
Does it?
–
Ste 8
Ste 7
7
Disconnect distributor 4-way connector. Con-
nect Ohmmeter between CKT 423 and ground
(–).
–
Step 9
Step 10
7
( ).
Resistance should have gone high (open cir-
cuit).
Does it?
–
Ste 9
Ste 10
8
Reconnect ECM and idle engine for 1 minute
or until code 42 sets.
Does Code 42 Set?
–
Step 11
Step 12
9
CKT 424 open, faulty connections, or faulty
ignition module.
–
–
–
10
CKT 423 shorted to ground.
–
–
–
11
Faulty ECM.
–
–
–
12
Code 42 is intermittent. Refer to “Diagnostic
Aids.”
–
–
–
13
Disconnect ignition module 4-way connector.
–
Step 14
Step 15
13
Is test light on?
–
Ste 14
Ste 15
14
CKT 424 shorted to ground.
–
–
–
15
Faulty ignition module.
–
–
–
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