Hummer H1 Service Manual page 1148

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DTC P0370 - Timing Reference High Resolution
Step
1 Important: Before clearing DTC(s) use the scan tool "Capture Info".
Was the "On-Board Diagnostic (OBD) System Check" performed?
2 1. Ignition "OFF".
2. Disconnect the Optical/Fuel temperature sensor electrical connector.
3. Ignition "ON" engine "OFF".
4. Using a J–39200, measure voltage between the Optical/Fuel temperature
5 volt reference circuit and chassis ground at harness connector.
Is voltage at the specified value?
3 1. Verify the optical sensor is disconnected.
2. Probe the sensor ground circuit with a test light connected to B+ at the
harness connector.
Is the test light ON?
4 1. Reconnect the Optical/Fuel temperature sensor.
2. Start the engine
3. Allow the engine to idle at the normal operating temperature.
4. Use a Scan Tool in order to command a 900 RPM idle.
5. With J39200 On the Hertz (Hz) scale, back probe a high resolution signal
circuit at the PCM.
Is the Hertz reading at the specified value?
5 1. Remove the electrical harness filter from the vehicle.
2. Check the resistance on the electical harness filter 5 volt reference circuit
(terminal A)
Is the resistance greater than the specified value?
6 1. Turn the ignition off.
2. Remove the electrical harness filter from the vehicle.
3. Disconnect the PCM.
4. Check the Optical/Fuel temperature 5 volts reference circuit for and
open, short to ground, or short to the sensor ground circuit.
5. If the Optical/Fuel temperature 5 volt reference circuit is open or shorted
to ground, repair as necessary.
Was the Optical/Fuel temperature 5 volt reference circuit open or shorted to
ground?
7 1. Check for and open or a poor sensor ground terminal connection at the
PCM.
2. If a problem is fournd, repair as necessary.
Was a repair performed?
8 Check the Opitical/Fuel temperature 5 volt reference circuit for a poor con-
nection at the PCM and replace the terminal if necessary.
Did the terminal require replacement?
05745159
Action
PCM/Tech 1 Scan Tool 83
Value(s) Yes
— Go to Step 2.
.24 v Go to Step 3.
Go to Step 4.
3840 Hz (+/ Go to Step10
-100)
2.0Ω go to step 13
— Go to Step 14. Go to Step 8.
— Go to Step 14. Go to Step 12.
— Go to Step 14. Go to Step 14.
No
Go to OBD
System Check.
Go to Step 5.
Go to Step 7
Go to Step 9
go to step 6