Hummer H2. Manual - part 1082

SELF DIAGNOSTIC SYSTEM

RETRIEVING DIAGNOSTIC TROUBLE CODES

See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM under
appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.

CLEARING DIAGNOSTIC TROUBLE CODES

See CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM under appropriate
SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DIAGNOSTIC TESTS

DTC P0562: LOW SYSTEM VOLTAGE

1. If diagnostic system check was not performed, perform ENGINE ELECTRICAL DIAGNOSTIC

SYSTEM CHECK under ON-VEHICLE TESTING. If diagnostic system check was performed, go to
next step.

2. Using scan tool, observe Ignition 1 Signal voltage in Powertrain Control Module (PCM) data list. If

voltage is 10.5 volts or less, go to next step. If voltage is greater than 10.5 volts, go to step 4 .

3. Test ignition feed circuit to PCM for high resistance or an open. If problem exists, repair as necessary.

NOTE:

Diagnostic trouble code tests are written specifically for use with GM Tech I or
Tech II scan tools. Generic scan tool can be used but may have limited
functions. This article only covers the portion of those systems which relates to
charging system diagnosis. For further information, see appropriate SELF-
DIAGNOSTICS article in ENGINE PERFORMANCE.

DTC

(1)

Description

P0562

Low System Voltage

P0563

High System Voltage

P0615

Improper Voltage Level On The Output Circuit That Controls The Starter

Relay

P0622

Out-Of-Range Duty Cycle Signal

P1637

Generator Turn-On Signal Circuit Voltage Out-Of-Range

P1638

Out-Of-Range Duty Cycle Signal

(1)

Codes listed in this table are only for testing covered in this article. For complete
DTC listing, see appropriate BODY CONTROL MODULES article in
ACCESSORIES & EQUIPMENT.

2004 Hummer H2

2003-04 STARTING & CHARGING SYSTEMS Generators & Regulators - H2

After repair, go to step 7 . If problem does not exist, go to step 5 .

4. Inspect PCM harness connectors for poor connections. If problem exists, repair as necessary. After repair,

go to step 7 . If problem does not exist, go to step 6 .

5. Repair ignition feed circuit to PCM for an open or short to ground. After repair, go to step 7 .

6. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - TRUCKS article in ENGINE

PERFORMANCE. Program PCM. After repair, go to next step.

7. Using scan tool, clear DTCs. Operate vehicle at more than 5 MPH, for 20 seconds at 1200 RPM. Check

for DTC. If DTC P0562 resets, repeat test beginning at step 2 . If DTC P0562 does not reset, system is
okay.

DTC P0563: HIGH SYSTEM VOLTAGE

Diagnostic Procedure

1. If diagnostic system check was not performed, perform ENGINE ELECTRICAL DIAGNOSTIC

SYSTEM CHECK under ON-VEHICLE TESTING. If diagnostic system check was performed, go to
next step.

2. Turn off all accessories. Using a DVOM, measure battery voltage while operating engine above 2000

RPM. If battery voltage is 19 volts or less, go to step 4 . If battery voltage is greater than 19 volts, go to
next step.

3. Replace generator. See GENERATOR under REMOVAL & INSTALLATION. After repair, go to step

5 .

4. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - TRUCKS article in ENGINE

PERFORMANCE. Program PCM. After repair, go to next step.

5. Using scan tool, clear DTCs. Operate vehicle at more than 5 MPH, for 20 seconds at 1200 RPM. Check

for DTC. If DTC P0563 resets, repeat test beginning step 2 . If DTC P0563 does not reset, system is okay.

DTC P0615: IMPROPER VOLTAGE LEVEL ON OUTPUT CIRCUIT THAT CONTROLS STARTER
RELAY

Circuit Description

The PCM uses Output Driver Modules (ODM) to control many functions of the engine. The ODMs supply the
ground path for the PCM controlled device when the PCM commands the device ON. Each ODM is able to
control several outputs. The PCM monitors the ODMs for circuit conditions that are incorrect for the
commanded state of the ODM. If the PCM detects an improper circuit condition in the ODM that controls the
starter relay, DTC P0615 will set.

Conditions For Running The DTC

System voltage is between 8-16 volts.

DTC Set Conditions

The PCM detects an improper voltage level on the output circuit that controls the starter relay. The condition

2004 Hummer H2

2003-04 STARTING & CHARGING SYSTEMS Generators & Regulators - H2

exists for at least 2 seconds.

Conditions For Clearing MIL/DTC

The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. The
DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

Ignition system DTC's set with the ignition switch in the START position if the starter relay or the starter is
inoperative. When the PCM enables starter operation, the PCM also initiates the diagnostic test routines for
DTC P0335. If a condition exists which prevents the engine from cranking, the PCM will not receive signal
input from the CKP and CMP sensors, and the DTC's will set.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may assist in diagnosing the
condition. The information may help determine how often the condition that set the DTC occurs.

Test Description

The list below refers to the step number(s) on the diagnostic procedure.

1. 1) Listen for an audible click when the Start 1 relay operates. Turn the ignition switch back and forth

from the ON to START positions. Repeat this as necessary. See step 2 in DIAGNOSTIC PROCEDURE.

2. 2) Tests for voltage at the coil side of the Start 1 relay. The PCM IGN fuse supplies power to the coil side

of the Start 1 relay. See step 3 in DIAGNOSTIC PROCEDURE.

3. 3) Verifies that the PCM is providing ground to the Start 1 relay. See step 4 in DIAGNOSTIC

PROCEDURE.

4. 4) Tests if ground is constantly being applied to the Start 1 relay. See step 5 in DIAGNOSTIC

PROCEDURE.

Diagnostic Procedure

1. If diagnostic system check was not performed, perform ENGINE ELECTRICAL DIAGNOSTIC

SYSTEM CHECK under ON-VEHICLE TESTING. If diagnostic system check was performed, go to
next step.

2. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel.

Install a scan tool. See COMPONENT LOCATIONS . Turn ON the ignition, with the engine OFF.
Turn the ignition back and forth from the ON to START positions. If Start 1 relay turns ON and OFF
with each command, problem is intermittent. Check wiring and connections. If problem is detected, go to
next step.

3. Turn OFF the ignition. Disconnect the Start 1 relay. Turn ON the ignition, with the engine OFF. Probe

the battery positive voltage of the Start 1 relay coil circuit with a test light that is connected to a good
ground. If test light illuminates, go next step. If test light does not illuminate, go to step 8 .

NOTE:

The PCM will not illuminate the Malfunction Indicator Light (MIL). The PCM will
store the conditions present when the DTC set as Fail Records data only.

2004 Hummer H2

2003-04 STARTING & CHARGING SYSTEMS Generators & Regulators - H2

4. Connect a test light between the control circuit of the Start 1 relay and the battery positive voltage of the

Start 1 relay coil circuit. Turn the ignition back and forth from the ON to START positions. If test light
turns ON and OFF with each command, go to step 6 . If test light does not turn ON and OFF with each
command, go next step.

5. Test the control circuit of the Start 1 relay for a short to voltage or an open. See WIRING DIAGRAMS .

When repair is complete, go to step 11 . If problem is not detected, go to step 7 .

6. Inspect for poor connections at the Start 1 relay. Check for intermittent and poor connections and possible

connector defects. When repair is complete, go to step 11 . If problem is not detected, go to step 9 .

7. Inspect for poor connections at the PCM. Check for intermittent and poor connections and possible

connector defects. When repair is complete, go to step 11 . If problem is not detected, go to step 10 .

8. Repair the battery positive voltage circuit of the Start 1 relay as necessary. See WIRING DIAGRAMS .

When repair is complete, go to step 11 .

9. Replace the Start 1 relay. See COMPONENT LOCATIONS . When replacement is complete, go to step

11 .

10. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - TRUCKS article in ENGINE

PERFORMANCE. Program PCM. After repair, go to next step.

11. Review and record the scan tool Fail Records data. Use the scan tool in order to clear the DTC. Operate

the vehicle within the Conditions for Running the DTC as specified in the supporting text. See
CONDITIONS FOR RUNNING THE DTC . Using the scan tool, observe the Specific DTC
Information for DTC P0615 until the test runs. If the scan tool indicates that DTC P0615 is set, go to step
2 and retest. If DTC does not set, system is OK.

DTC P0622 OR DTC P1638: OUT-OF-RANGE DUTY CYCLE SIGNAL

Circuit Description

The PCM uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The
generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A Pulse-
Width Modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The
PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust
the idle speed to compensate for high electrical loads.

The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN
position and the engine is OFF, the PCM should detect a duty cycle near zero percent. However, when the
engine is running, the duty cycle should be between 5 percent and 100 percent. The PCM monitors the PWM
signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal,
DTC P0622 or DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the
IPC to illuminate the charge indicator.

Conditions For Running The DTC

Key ON Test

No generator, CKP sensors, or CMP sensor DTCs are set.

The key is in the RUN position.

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2003-04 STARTING & CHARGING SYSTEMS Generators & Regulators - H2

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