Hummer H1 Service Manual page 1140

_____________________________________________________
®
DTC P0251 - Injection Pump Cam System
Step
1 Important: Before clearing DTC(s) use the scan tool "Capture Info".
Was the "On-Board Diagnostic (OBD) System Check" performed?
2 Start and idle engine. With the throttle closed, observe the Cam Ref Missed
display on scan tool. Does scan tool display specified value?
3 DTC is intermittent.
Are additional DTCs stored?
4 1. Ignition "OFF".
2. Disconnect the Optical/Fuel temperature sensor electrical connector.
3. Ignition "ON" engine "OFF".
4. Measure voltage between Optical/Sensor 5 volt circuit and chassis ground
at harness connector. Is voltage at specified value?
5 Probe the sensor ground circuit with a test light connected to B+ at the har-
ness connector. Is test light "ON"?
6 1. Reconnect the Optical/Fuel temperature sensor.
2. Start and idle engine.
3. With scan tool, command 900 rpm.
4. On Hertz (Hz) scale, back probe Cam signal circuit at PCM.
Is Hertz reading at specified value?
7 1. Remove electrical harness filter from vehicle.
2. Check resistance on 5 volt reference circuit (terminal "A").
Is resistance greater than specified value?
8 1. Ignition "OFF".
2. Electrical harness filter removed from vehicle.
3. Disconnect the PCM and check the Optical/Sensor 5 volt circuit for an
open, short to ground, or short to the sensor ground circuit.
4. If Optical/Sensor 5 volt circuit is open or shorted to ground, repair it as
necessary.
Was 5 volt circuit open or shorted to ground?
9 1. Check for open or poor sensor ground terminal connection at PCM.
2. If a problem is found, repair as necessary.
Was a repair performed?
10 Check the Optical/Fuel Temperature 5 volt reference circuit for a poor con-
nection at the PCM and replace terminal if necessary.
Did the terminal require replacement?
11 1. Ignition "OFF".
2. Check the Cam signal circuit for an open or short to ground.
3. If Cam signal circuit is open or shorted to ground, repair it.
Was the Cam signal circuit open or shorted to ground?
12 Check for a poor connection at the PCM harness terminal and replace.
Did the terminal require replacement?
13 Replace injection pump.
Is action complete?
14 Replace the faulty PCM. Notice: If the PCM is faulty, the new PCM must be
programmed. Is the action complete?
15 Replace electrical harness filter.
Is action complete?
05745159
Action
PCM/Tech 1 Scan Tool 75
Value(s) Yes
— Go to Step 2.
8 Go to Step 4. Go to Step 3.
— Go to DTC
table.
5v Go to Step 5.
— Go to Step 6.
60 Hz Go to Step 12. Go to Step 11.
(± 3 Hz)
2.0 Ohms Go to Step 15. Go to Step 8.
— Go to Step 16. Go to Step 10.
— Go to Step 16. Go to Step 14.
— Go to Step 16. Go to Step 14.
— Go to Step 16. Go to Step 13.
— Go to Step 16. Go to Step 14.
— Go to Step 16.
— Go to Step 16.
— Go to Step 16.
No
Go to OBD
System Check.
Go to
Diagnostic
Aids.
Go to Step 7.
Go to Step 8.
—
—
—