TROUBLE CODE DIAGNOSTICS - 7.4L MPI SERVICE MANUAL NUMBER 23
Page 5G-30 90-861326--1 MARCH 1999
Code 42 (3 of 3): Ignition Control (IC) Circuit (Non-Scan) - Grounded IC Circuit,
Open Bypass Circuit, or Grounded Bypass Circuit
STEP ACTION VALUE YES NO
PROCEED TO
3 1. Ignition “OFF.”
2. Disconnect ECM harness connectors.
3000 to
3. Using a DVOM set on OHMS, probe
ECM harness terminal J2-23 to ground.
6000
Ohms
Is resistance within specified value?
Step 4 Step 8
4
1. Leave DVOM connected from ECM har-
ness terminal J2-23 to ground.
2. Using a test light connected to battery
positive (B+), probe ECM harness terminal
J2-24.
1000
3. As the test light contacts J2-24, the resis-
tance should switch from 3000 Ohms to under
1000 Ohms.
Ohms
Does the resistance switch to under the
specified value?
Step 7 Step 5
5
Using a test light connected to battery positive
(B+), probe ECM harness terminal J2-24
(CKT424).
Does light illuminate?
– Step 6 Step 9
6 Disconnect ignition module 4-way connector.
Does test light illuminate?
– Step 10 Step 11
7
1. Reconnect ECM.
2 Start engine and idle for 2 minutes or Ma-
.
-
rine Diagnostic Code Tool indicates a stored
.
Is trouble code 42 present?
– Step 12 Step 13
8
Locate and repair short to ground in CKT 423.
If a problem is found, repair as necessary.
Was
a problem found?
– Step 11
9
Locate and repair open CKT 424. If a problem
is found, repair as necessary.
Was a problem
found?
–
Verif
Step 11
10
Locate and repair short to ground in CKT 424.
Is action complete?
–
Repair
–
11
Replace faulty ignition module.
Is action com-
plete?
– –
12
Repair faulty ECM connections or replace
faulty ECM.
Is action complete?
– –
13
Trouble code 42 is intermittent. Refer to “Diag-
nostic Aids” on facing page. Check harness
and connectors for an intermittent open or
short to ground in CKT 424, or an intermittent
short to ground in CKT 423.
– – –
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