Content .. 1081 1082 1083 1084 ..

Hummer H2. Manual - part 1083

The engine is not running.

Run Test

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

The engine is less than 3000 RPM.

Conditions For Setting The DTC

Conditions for Setting the DTC During the ignition ON test, the PCM detects a PWM signal is out of
range.

During the RUN test, the PCM detects a PWM signal less then 5 percent for more than 6 seconds.

Action Taken When The DTC Sets

The PCM will store the conditions present when the DTC set as Fail Records data only.

The Malfunction Indicator Light (MIL) will not illuminate.

Conditions For Clearing The DTC

The conditions for setting the DTC are no longer present.

A history DTC will clear after 40 malfunction free ignition cycles.

The Powertrain Control Module (PCM) receives the clear code command from the scan tool.

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.

Start engine. Using scan tool, observe GEN F-Terminal parameter in Powertrain Control Module (PCM)
data list. If scan tool indicates GEN F-Terminal parameter is 5-95 percent, go to next step. If scan tool
does not indicate GEN F-Terminal parameter is 5-95 percent, go to step 4 .

3. With the scan tool command the generator OFF. If scan tool indicates GEN F-Terminal parameter is zero

percent, problem is intermittent. Check wiring and connections. If scan tool does not indicate GEN F-
Terminal parameter is zero percent, go to next step.

4. Turn OFF the ignition. Disconnect the generator connector. Connect test light to battery positive voltage.

Turn ON the ignition, with the engine OFF. Probe the F-Terminal in the generator connector. See
WIRING DIAGRAMS . Observe the GEN F-Terminal Signal parameter in the PCM data list. If scan
tool indicates GEN F-Terminal parameter is 100 percent, perform TEST A: CHARGING SYSTEM
TEST under SYSTEM TESTS. If scan tool does not indicate GEN F-Terminal parameter is 100 percent,
go to next step.

5. Test Gray wire for short or open between generator harness connector terminal "C" and PCM harness

connector C2 terminal No. 75. See WIRING DIAGRAMS . If problem exists, repair as necessary. After
repair, go to step 8 . If problem does not exist, go to next step.

2004 Hummer H2

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

6. Inspect PCM harness connector for poor connections. If problem exists, repair as necessary. After repair,

go to step 8 . If problem does not exit, go to next step.

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

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

8. Review and record scan tool Fail Records data. Using scan tool, clear DTCs. Operate vehicle within Fail

Records conditions as noted. Using scan tool, observe Specific DTC information for DTC P0622 or DTC
P1638. If scan tool indicates DTC P0622 or DTC P1638 failed this ignition, repeat test beginning at step
2 . If scan tool indicates DTC P0622 or DTC P1638 passed this ignition, system is okay.

DTC P1637: GENERATOR TURN-ON SIGNAL CIRCUIT VOLTAGE OUT-OF-RANGE

Circuit Description

The Powertrain Control Module (PCM) uses the generator turn on signal circuit to control the generator. A high
side driver within the PCM allows the PCM to turn the generator ON and OFF. When generator operation is
desired, the PCM sends a 10-11 volt signal to the voltage regulator via the generator turn on signal circuit. This
causes the voltage regulator to begin controlling the generator field circuit. Once the generator is enabled by the
PCM, the voltage regulator controls generator output independently of the PCM. Under certain operating
conditions, the PCM can turn Off the generator by turning Off the 10-11 volt signal on the generator turn on
signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal
circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage
regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the
generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.

Conditions For Running The DTC

The ignition is ON.

System voltage between 9.0-18.0 volts.

Conditions For Setting The DTC

An improper voltage level has been detected on the generator L-terminal circuit.

The above conditions are present for at least 30 seconds.

Action Taken When The DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records data only.

This information will not be stored as Freeze Frame Records.

Conditions For Clearing The MIL/DTC

The DTC becomes history when the conditions for setting the DTC are no longer present.

The history DTC clears after 40 malfunction free warm-up cycles.

The PCM receives a clear code command from the scan tool.

2004 Hummer H2

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

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. Install a scan tool. Start the engine. With a scan tool, monitor the DTC information for DTC P1637 in

Engine Controls. If the scan tool indicates that DTC P1637 has passed, problem is intermittent. Check
wiring and connections. If the scan tool does not indicate that DTC P1637 has passed, go to next step.

3. Test the generator turn on signal circuit for a short or open. If problem exists, repair as necessary. After

repair, go to step 6 . If problem does not exist, go to next step.

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

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

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

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

6. Using scan tool, clear DTCs. Operate vehicle at more than 1000 RPM. Check for DTC. If DTC P1637

resets, repeat test beginning at step 2 . If DTC P1637 does not reset, system is okay.

SYSTEM TESTS

SYMPTOM INDEX

TEST A: CHARGING SYSTEM TEST

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. Start engine and observe charge indicator on Instrument Panel Cluster (IPC) or message in Driver

Information Center (DIC). If charge indicator illuminates or DIC displays a charging system message, go
to next step. If charge indicator light does not illuminate or DIC does not display a charging system
message, repair by symptom. See SYMPTOM INDEX table.

Turn ignition switch to OFF position. Using CS Generator Tester (J-41450-B), connect Red lead to

Symptom

Perform Test

Charging System Test

Charge Indicator Always On

Charge Indicator Inoperative

Generator Noise Diagnosis

NOTE:

Ensure battery is in good condition before proceeding with charging system
tests. See BATTERY TESTING & INSPECTION under ON-VEHICLE TESTING.

NOTE:

Green POWER light of tester should remain illuminated while tester is
being used.

2004 Hummer H2

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

generator output terminal (BAT) and Black lead to metal generator housing. If Green POWER light does
not illuminate, go to next step. If Green POWER light illuminates, go to step 6 .

4. Using a DVOM, measure voltage between output terminal (BAT) of generator and metal generator

housing. If battery voltage exists, go to step 14 . If battery voltage does not exist, go to next step.

5. Measure voltage between generator output terminal and battery negative terminal. If battery voltage

exists, go to step 12 . If battery voltage does not exist, go to step 11 .

Connect carbon pile tester to battery. Connect inductive ammeter to output circuit of generator.
Disconnect generator harness connector. Locate matching harness connector on CS Generator Tester (J-
41450-B) and connect to generator. If Red DIAGNOSTIC light illuminates, go to next step. If Red
DIAGNOSTIC light does not illuminate, go to step 13 .

7. Increase engine speed to 2500 RPM. If Red DIAGNOSTIC light does not illuminate, go to next step. If

Red DIAGNOSTIC light illuminates, go to step 15 .

Maintain engine speed at 2500 RPM. Turn on load of carbon pile tester and increase load until load is
equal to test value of generator. See GENERATOR SPECIFICATIONS . If Red DIAGNOSTIC light
illuminates, go to step 15 . If Red DIAGNOSTIC light does not illuminate, go to next step.

9. Maintain engine speed at 2500 RPM and continue to operate generator at load test value. See

GENERATOR SPECIFICATIONS . Using a DVOM, measure voltage drop between generator output
terminal and positive battery terminal. If voltage drop is 0.5 volt or less, go to next step. If voltage drop is
greater than 0.5 volt, go to step 11 .

10. Maintain engine speed at 2500 RPM and continue to operate generator at load test value. See

GENERATOR SPECIFICATIONS . Using a DVOM, measure voltage drop between generator metal
housing and negative battery terminal. If voltage drop is 0.5 volt or less, go to step 16 . If voltage drop is
greater than 0.5 volt, go to step 12 .

11. Repair open or high resistance in generator output circuit. See WIRING DIAGRAMS . After repair, go

to step 16 .

12. Repair open or high resistance in generator ground circuit. See WIRING DIAGRAMS . After repair, go

to step 16 .

13. Disconnect Generator Tester harness connector, but leave alligator clips connected so Green POWER

light remains illuminated. Connect a jumper with a 100 ohm in-line resistor between generator connector
terminal "B" and ground. If Red DIAGNOSTIC light illuminates, go to step 15 . If Red DIAGNOSTIC
light does not illuminate, go to next step.

14. If a problem exists with CS Generator Tester (J-41450-B). Refer to manufacturer's instructions, how to

test generator tester for proper operation. If tester has been repaired or replaced, go to step 3 .

15. Replace generator. See GENERATOR under REMOVAL & INSTALLATION. After repair, go to next

step.

CAUTION: Ensure load is completely turned off before connecting or

disconnecting carbon pile load tester to battery.

NOTE:

If generator is not capable of producing Load Test amps, operate
generator at maximum possible output.

2004 Hummer H2

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

Content .. 1081 1082 1083 1084 ..