Hummer H1 Service Manual page 1177

112 PCM/Tech 1 Scan Tool
DTC P1635 - PCM 5 Volt Reference Low
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 installed.
2. Crank engine for 15 seconds or start up.
Does DTC reset?
3 1. Ignition ON, engine OFF>
2. Disconnect Boost/BARO sensor.
3. With J–39200 DVM, probe 5 volt reference circuit at harness connec-
tor.
Is voltage less than the specified value?
4 1. Disconnect PCM connector with the boost sensor 5 volt reference cir-
cuit.
2. With test light connected to B+, probe 5 volt reference circuit at PCM
harness.
Is test light ON?
5 DTC is intermittent. If no additional DTCs are stored, refer to "Diagnostic
Aids". If additional DTCs are stored, refer to those charts(s) first.
Are additional DTCs stored?
6 Replace Boost/BARO sensor.
7 Repair short to ground in 5 volt reference circuit.
Is the action complete?
8 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?
9 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?
10 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.
4.0v Go to Step 4.
— Go to Step 7.
— Go to
applicable
DTC table.
— Go to Step 8.
— Go to Step 8.
— Go to Step 9.
— Go to Step 6.
— Go to the
applicable
DTC table
®
No
Go to OBD
System Check.
Go to Step 5.
Go to Step 6.
Go to Step 8.
Go to
Diagnostic
Aids
—
—
Go to Step 8.
Go to Step 2.
System OK.