Hummer H1 Service Manual page 1073

8 PCM/Tech 1 Scan Tool
No Malfunction Indicator Lamp (MIL) "Check Engine"
Step
1 Was the "On-Board Diagnostic (OBD) System Check"
performed?
2 Attempt to start the engine.
Does the engine start?
3 Check the fuse number 4.
Is the fuse OK?
4 Turn the ignition "ON," probe the ignition feed circuit at
the cluster connector with a test light to ground.
Is the test light "ON?"
5 1. Turn the ignition "OFF."
2. Disconnect the black PCM connector.
3. Turn the ignition "ON."
4. Connect a fused jumper to the MIL control circuit at
the PCM connector.
5. Observe the MIL.
Is the MIL "ON?"
6 Check the PCM ignition Feed and Battery Feed fuses.
Are both of the fuses OK?
7 1. Turn the ignition "OFF."
2. Disconnect the PCM connectors.
3. Turn the ignition "ON."
4. Probe the PCM harness ignition and battery feed cir-
cuits with a test light to ground.
Is the test light "ON" both circuit?
8 1. Check for a faulty PCM ground or a poor PCM ground
connection.
2. If a problem is found, repair as necessary.
Was a problem found?
9 1. Check for a poor connection at the PCM.
2. If a poor connection is found, repair as necessary.
Was a problem found?
10 1. Check the MIL control circuit for an open.
2. If the MIL control circuit is open, repair as necessary.
Was a problem found?
11 Repair open in the ignition feed circuit to the cluster con-
nector.
Is the action complete?
12 Locate and repair open in the PCM battery feed circuit or
the PCM ignition feed circuit as necessary.
Is the action complete?
13 Locate and repair short to ground in the PCM Ignition
Feed circuit or the PCM Battery Feed circuit as neces-
sary.
Is the action complete?
______________________________________________________
Action Value(s) Yes
Go to Step 2
—
— Go to Step 3
— Go to Step 4
— Go to Step 5
— Go to Step 9
— Go to Step 7
— Go to Step 8
— Go to Step 20
— Go to Step 20
— Go to Step 20
— Go to Step 20
— Go to Step 20
Go to Step 20
—
®
No
Go to OBD System
Check
Go to Step 6
Go to Step 14
Go to Step 11
Go to Step 10
Go to Step 13
Go to Step 12
Go to Step 9
Go to Step 15
Go to Step 16
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