Hummer H1 Service Manual page 1179

114 PCM/Tech 1 Scan Tool
DTC P1641 - Malfunction Indicator Lamp (MIL) Control Circuit
Step
1 Important: Before clearing DTC(s) use the scan tool "Capture Info" to
record freeze frame and failure records for reference, as data will be lost
when "Clear Info" function is used.
Was the "On-Board Diagnostic (OBD) System Check" performed?
2 1. Scan tool connected.
2. Ignition "ON" engine "OFF".
Is the MIL "OFF"?
3 1. Ignition "OFF".
2. Disconnect the blue 32 way PCM electrical connector.
3. Ignition "ON" engine "OFF".
Is the MIL "ON"?
4 MIL control circuit is shorted to ground.
Is the action complete?
5 1. Check the MIL control circuit for the following:
• opens
• poor connection at PCM
• faulty bulb
• faulty fuse.
Was a problem found?
6 Replace the faulty PCM. Notice: If the PCM is faulty, the new PCM must
be programmed. Go to PCM replacement and programming procedures.
Is the action complete?
7 1. Using the Scan Tool, select "DTC", "Clear Info".
2. Start engine and idle at normal operating temperature.
3. Select "DTC", "Specific", then enter the DTC number which was set.
4. Operate vehicle within the conditions for setting this DTC as specified in
the supporting text.
Does the Scan Tool indicate that this diagnostic Ran and Passed?
8 Using the Scan Tool, select "Capture Info", "Review Info".
Are any DTCs displayed that have not been diagnosed?
___________________________________________________
Action Value(s) Yes
— Go to Step 2.
— Go to Step 3.
— Go to Step 4.
— Go to Step 7.
— Go to Step 7.
— Go to Step 7.
— Go to Step 8.
— Go to the
applicable
DTC table
®
No
Go to OBD
System Check.
Go to Step 5.
Go to Step 6.
—
Go to Step 6.
—
Go to Step 2.
System OK.