Hummer H2. Manual - part 1148

7. Inspect for poor connections at the PCM. Did you find and correct the condition? If yes, go to step 11 . If

no, go to step 10 .

8. Repair the battery positive voltage circuit of the Start 1 relay. After repairs, go to step 11 .

9. Replace the Start 1 relay. Did you complete the replacement? After replacement, go to step 11 .

10.

Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement. After replacement, 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 DTC . Using the scan tool, observe the Specific
DTC Information for DTC P0615 until the test runs. Does the scan tool indicate that DTC P0615 failed
this ignition? If yes, go to step 2 . If no, system OK.

DTC P1637

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 DTC

The ignition is ON.

System voltage between 9.0-18.0 volts.

Conditions For Setting DTC

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

The conditions are present for at least 30 seconds.

Action Taken When DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information
will not be stored as Freeze Frame Records.

Conditions For Clearing DTC

NOTE:

The replacement PCM must be programmed.

2004 Hummer H2

2004 STARTING & CHARGING SYSTEMS Starters - H2

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.

Diagnostic Procedures

1. Did you perform the Engine Electrical Diagnostic System Check? If yes, go to next step. DIAGNOSTIC

SYSTEM CHECK - ENGINE ELECTRICAL .

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

Engine Controls. Does the scan tool indicate that DTC P1637 has passed? If yes, problem is intermittent.
If no, go to next step.

3. Turn ON the ignition, leaving the engine OFF. Disconnect the generator harness connector. Measure the

voltage between the generator turn on signal circuit and ground. Does the voltage measure near 10-11
volts? If yes, go to step 5 . If no, go to next step.

4. Test the generator turn on signal circuit for a short or open. Did you find and correct the condition? If yes,

go to step 8 . If no, go to step 6 .

5. Inspect for poor connections at the harness connector of the generator. Did you find and correct the

condition? If yes, go to step 8 . If no, go to GENERATORS & REGULATORS .

6. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition?

If yes, go to step 8 . If no, go to next step.

Replace the PCM/ECM. Refer to Powertrain Control Module (PCM) Replacement. Is action complete? If
yes, go to next step.

8. Use the scan tool in order to clear the DTCs. Operate the vehicle within the CONDITIONS FOR

RUNNING DTC . System OK

SYMPTOMS - ENGINE ELECTRICAL

Perform DIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL before using the Symptom
Tables in order to verify that all of the following are true:

A. There are no DTCs set.

B. The control module(s) can communicate via the serial data link.

Review the system operation in order to familiarize yourself with the system functions. Refer to one of
the following system operations:

A. Battery Description and Operation.

B. Starting System Description and Operation. See DESCRIPTION & OPERATION .

C. Charging System Description and Operation. See GENERATORS & REGULATORS .

NOTE:

The replacement PCM must be programmed.

NOTE:

The following steps must be completed before using the symptom tables.

2004 Hummer H2

2004 STARTING & CHARGING SYSTEMS Starters - H2

VISUAL/PHYSICAL INSPECTION

Inspect for aftermarket devices which could affect the operation of the Starting and Charging Systems.

Inspect the easily accessible or visible system components for obvious damage or conditions which could
cause the symptom.

INTERMITTENT

Faulty electrical connections or wiring may be the cause of intermittent conditions. Check for intermittent and
poor connections in wiring systems.

SYMPTOM LIST

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom:

Starter Solenoid Does Not Click. See STARTER SOLENOID DOES NOT CLICK .

Starter Solenoid Clicks, Engine Does Not Crank. See STARTER SOLENOID CLICKS, ENGINE
DOES NOT CRANK .

Engine Cranks Slowly. See ENGINE CRANKS SLOWLY .

Battery Inspection/Test. See BATTERY INSPECTION/TEST (NON-HP2) .

Charge Indicator Always On. See CHARGE INDICATOR ALWAYS ON .

Charge Indicator Inoperative. See CHARGE INDICATOR INOPERATIVE .

Charging System Test. See CHARGING SYSTEM TEST (CS/AD/SI GENERATORS) .

Generator Noise Diagnosis. See GENERATOR NOISE DIAGNOSIS .

TROUBLE SHOOTING

STARTER SOLENOID DOES NOT CLICK

1. Did you preform the Engine Electrical Diagnostic System Check? If yes, go to next step. If no, go to

DIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL .

2. Turn the ignition switch to the START position. Does the engine crank? If yes, problem is intermittent. If

no, go to next step.

3. Turn the ignition switch to the START position. Does the starter motor relay click? If yes, go to step 11 .

If no, go to next step.

4. Turn OFF the ignition. Disconnect the powertrain control module (PCM) harness connector. Connect a

test lamp between the Crank Voltage circuit of the PCM harness and a good ground. With the
transmission in park, turn the ignition switch to the START position. Does the test light illuminate? If
yes, go to step 7 . If no, go to next step.

5. Inspect for poor connections at the PCM connector, Underhood Fuse Block or ignition switch harness

connector. Did you find and correct the condition? If yes, go to step 29 . If no, go to next step.

6. Test the supply voltage circuit of the crank voltage circuit and Crank fuse for an open or high resistance.

Did you find and correct the condition? If yes, go to step 29 . If no, go to step 27 .

2004 Hummer H2

2004 STARTING & CHARGING SYSTEMS Starters - H2

7. Turn OFF the ignition. Disconnect the PCM harness connector. Connect a test lamp between the crank

voltage circuit (starter enable relay control) of the PCM harness and a good ground. Turn the ignition to
the START position. Does the test lamp illuminate? If yes, go to step 19 . If no, go to next step.

8. Remove the starter motor relay. Connect a test light from the supply voltage circuit of the starter motor

relay coil circuit to ground. With the transmission in park, or clutch pedal depressed, turn the ignition
switch to the START position. Does the test light illuminate? If yes, go to next step. If no, go to step 10 .

9. Connect a test light from the supply voltage circuit of the starter motor relay coil circuit to the control

circuit of the starter motor relay coil circuit. With the transmission in park, or clutch pedal depressed, turn
the ignition switch to the START position. Does the test light illuminate? If yes, go to step 17 . If no, go
to step 14 .

10. Turn OFF the ignition. Disconnect the Park Neutral Position (PNP) switch. Refer to Automatic

Transmissions. Turn ON the ignition, with the engine OFF. Connect a 10 amp fused jumper between the
starter motor relay coil control circuits of the PNP switch or clutch pedal position switch. With the
transmission in park, or clutch pedal depressed, turn the ignition switch to the START position. Does the
test lamp illuminate? If yes, go to step 18 . If no, go to step 15 .

11. Turn OFF the ignition. Disconnect the starter motor relay. Connect a test lamp between the battery

positive voltage circuit of the starter motor relay switch circuit and a good ground. Does the test lamp
illuminate? If yes, go to next step. If no, go to step 23 .

12. Connect a 30 amp fused jumper between the battery positive voltage circuit of the starter motor relay

switch circuit and the supply voltage circuit of the starter solenoid. Does the engine crank? If yes, go to
step 17 . If no, go to next step.

13. Does the fuse in the jumper open? If yes, go to step 24 . If no, go to step 16 .

14. Test the control circuit of the starter motor relay for an open or high resistance. Did you find and correct

the condition? If yes, go to step 29 . If no, go to step 25 .

15. Test the supply voltage circuit of the starter motor relay coil circuit for an open or high resistance. Did

you find and correct the condition? If yes, go to step 29 . If no, go to step 21 .

16. Test the supply voltage circuit of the starter solenoid for an open or high resistance. Did you find and

correct the condition? If yes, go to step 29 . If yes, go to step 22 .

17. Inspect for poor connections at the starter motor relay. Did you find and correct the condition? If yes, go

to step 29 . If no, go to step 25 .

18. If equipped with an Automatic Transmission, inspect for poor connection at the PNP switch harness

connector. If OK, perform the Park/Neutral Position Switch Adjustment 4L60-E for Automatic
Transmission. If equipped with a Manual Transmission, inspect for poor connection at the clutch pedal
position switch harness connector. Did you find and correct the condition? If yes, go to step 29 . If no, go
to step 26 .

19. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition?

If yes, go to step 29 . If no, go to next step.

20.

Replace the PCM/ECM. Refer to PCM Replacement. After replacement, go to step 29 .

21. Inspect for poor connections at the ignition switch harness connector. Did you find and correct the

condition? If yes, go to step 29 . If no, go to step 27 .

NOTE:

The replacement PCM must be programmed.

2004 Hummer H2

2004 STARTING & CHARGING SYSTEMS Starters - H2

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