SERVICE MANUAL NUMBER 23
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
90-861326--1 MARCH 1999 Page 5F-33
Code 42 (3 of 3): Ignition Control (IC) Circuit (Scan)
1. Ignition OFF.
2. Disconnect ECM connectors.
3. Ignition ON.
4
4. Use a DVOM with selector in the OHMS
range.
5. Probe ECM harness connector CKT 423
with DVOMto ground.
It should read more than 3000 Ohms.
Does it?
– Step 5 Step 6
5
Probe ECM harness connector CKT 424 with a
test light to battery positive (B+).
Is test light on?
– Step 14 Step 7
6
Open CKT 423, faulty connection or faulty igni-
tion module.
– – –
With Ohmmeter connected to ECM harness
CKT 423 and ground, probe harness CKT 424
with test light connected to battery positive
(B+).
As test light contacts CKT 424, resistance
should change from over 3000 Ohms to under
1000 Ohms.
Does it?
– Step 9 Step 8
Disconnect distributor 4-way connector. Con-
nect ohmmeter between CKT 423 and ground.
Resistance should have gone high (open
circuit), does it?
– Step 10 Step 11
9
Reconnect ECM and idle engine for 1 minute
or until code 42 sets.
– Step 12 Step 13
10
CKT 424 open, faulty connections or faulty
ignition module.
– – –
11 CKT 423 shorted to ground. – – –
12 Faulty ECM. – – –
13
Code 42 is intermittent refer to “Diagnostic
Aids.”
– – –
14 Disconnect ignition module 4-way connector.
Is test light on?
– Step 15 Step 16
15 CKT 424 shorted to ground. – – –
16 Faulty ignition module. – – –
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