Hummer H1 (2002+). Manual - part 287

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PCM/Tech 1 Scan Tool 81

05745159

Using the Scan Tool, select “DTC”, “Clear Info”.
Start engine and idle at normal operating temperature.
Select “DTC”, “Specific”, then enter the DTC number which was set.
Operate vehicle within the conditions for setting this DTC.
Does the Scan Tool indicate that this diagnostic Ran and Passed?

—

Go to Step

15.

Go to Step

Using the Scan Tool, select “Capture Info”, “Review Info”.
Are any DTCs displayed that have not been diagnosed?

—

Go to the

DTC table

System OK.

DTC P0335 - Crankshaft Position Sensor Circuit Performance

Step

Action

Value(s)

Yes

PCM/Tech 1 Scan Tool

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DTC P0370 Timing Reference High
Resolution

Circuit Description

The optical sensor provides a high resolution signal to the
PCM by counting pulses on the sensor disk located in the injec-
tion pump. The high resolution is one of the most important in-
puts by the PCM for fuel control and timing. This test monitors
the number of high resolution pulses which have been missed
(not detected). It’s based on a comparison between the number
of pulses that were detected since the last pump cam pulse and
the number of the pulses that should have occurred. This is a
type A DTC.

Conditions for Setting the DTC

A number of High Resolution pulses (internal to PCM) per ev-
ery 8 cam reference pulses.

Action Taken When the DTC Sets

Backup fuel.

Conditions for Clearing the MIL/DTC

• The PCM will turn the MIL off after three consecutive

trips without a fault condition.

• A History DTC will clear when forty consecutive

warm-up cycles that the diagnostic does not fail (coolant
temperature has risen 5°C (40°F) from start up coolant

temperature and engine coolant temperature exceeds
71°C (160°F) that same ignition cycle).

• Use of a Scan Tool.

Diagnostic Aids

When PCM is in backup fuel, fast idle and poor performance
problems will exist. If P0251 is also stored, the snap shot mode
on the scan tool should be used to properly identify fault. It is
possible P0370 may set if there is air in fuel system (vehicle
running out of fuel).

Test Description

Number(s) below refer to the number(s) on the diagnostic ta-
ble.

2. This step will determine if there is a 5 volt reference.

3. This step checks the ground circuit.

4. This step will check to see if the sensor is sending a signal

back to the PCM.

5 VOLT
REFERENCE

OPTICAL/ FUEL
TEMP SENSOR

PUMP CAM

SENSOR

SIGNAL

HIGH

RESOLUTION

SIGNAL

SENSOR

GROUND

C12

375 GY

442 BR

703 OR

156 PK

225 YL

C27-D14

C29-A4

C29-A2

C27-D9

C27-C8

FUEL TEMP
SIGNAL

SENSOR
GROUND

HIGH
RES
SIGNAL

CAM
SENSOR
SIGNAL

5 VOLT
REFERENCE

INJECTION TIMING

STEPPEN MOTOR (ITS)

709 RD

708 TN

710 OR

1 YL

C29

A10

ITS
HI

ITS
LO

ITS
HI

POWERTRAIN

CONTROL

MODULE

9-S12-070

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PCM/Tech 1 Scan Tool 83

05745159

DTC P0370 - Timing Reference High Resolution

Step

Action

Value(s)

Yes

Important:

Before clearing DTC(s) use the scan tool “Capture Info”.

Was the “On-Board Diagnostic (OBD) System Check” performed?

—

Go to Step 2.

Go to OBD

System Check.

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?

.24 v

Go to Step 3.

Go to Step 5.

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?

Go to Step 4.

Go to Step 7

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?

3840 Hz (+/

-100)

Go to Step10

Go to Step 9

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?

2.0

Ω

go to step 13

go to step 6

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?

—

Go to Step 14.

Go to Step 8.

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?

—

Go to Step 14. Go to Step 12.

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?

—

Go to Step 14. Go to Step 14.

PCM/Tech 1 Scan Tool

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Turn the ignition OFF.

2. Disconnect the PCM.

3. Check the high resolution signal circuit for and open, short ot ground, or

short to the sensor ground circuit.

4. If the high resolutin signal circuit is open or shorted to ground, repair as

necessary.

5. Was the high resolution signal circuit open or shorted to ground?

—

Go to Step 14. Go to Step 11.

Check the high resolution signal circuit for a poor connection at the PCM
and replace terminal if necessary.

Did the terminal require replacement?

—

Go to Step 14. Go to Step 12.

Replace the injection pump.
Important: If injection pump is malfunctioning, the new injection pump
must be timed.
Is the action complete?

—

Go to Step 14.

—

Replace the PCM.
Important: The new PCM must be programmed.
Is the action complete?

—

Go to Step 14.

—

Replace the electrical harness filter.
Is the action complete?

—

Go to Step 14.

—

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.
Does the Scan Tool indicate that this diagnostic Ran and Passed?

—

Go to Step 15.

Go to Step 2.

Using the Scan Tool, select “Capture Info”, “Review Info”.
Are any DTCs displayed that have not been diagnosed?

—

Go to the

DTC table

System OK.

DTC P0370 - Timing Reference High Resolution

Step

Action

Value(s)

Yes

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