Hummer H2. Manual - part 1912

z

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

z

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

z

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.  

7.  

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 

z

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.  

z

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 

z

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

z

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:  

z

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

z

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

z

Engine Cranks Slowly. See ENGINE CRANKS SLOWLY .  

z

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

z

Charge Indicator Always On. See CHARGE INDICATOR ALWAYS ON .  

z

Charge Indicator Inoperative. See CHARGE INDICATOR INOPERATIVE .  

z

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

z

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

  

22. Inspect for poor connections at the starter solenoid. Did you find and correct the condition? If yes, go to 

step 29 . If no, go to step 28 .  

23. Repair the open or high resistance in the battery positive voltage circuit of the Starter Motor relay switch 

circuit. After repairs, go to step 29 .  

24. Repair the short to ground in the supply voltage circuit of the starter solenoid. After repairs, go to step 

29 .  

25. Replace the Starter Relay. After replacement, go to step 29 .  

26. Replace the PNP switch. Refer to Automatic Transmission. After replacement, go to step 29 .  

27. Replace the Ignition Switch. After replacement, go to step 29 .  

28. Replace the starter. Refer to STARTER MOTOR REPLACEMENT . After replacement, go to next 

step.  

29. Operate the system for which the symptom occurred. Did you correct the condition? If yes, system OK. If 

no, go to step 2 .  

STARTER SOLENOID CLICKS, ENGINE DOES NOT CRANK 

1. Did you perform 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 to the START position. Did the starter solenoid click? If yes, go to next step. If no, go to 

STARTER SOLENOID DOES NOT CLICK .  

3. Inspect the engine and belt drive system for mechanical binding (seized engine, seized generator). Does 

the engine move freely? If yes, go to next step. If no, go to Engine Mechanical.  

4. Test the battery positive cable between the battery and the starter solenoid for high resistance. Did you 

find and correct the condition? If yes, go to step 8 . If no, go to next step.  

5. Test the ground circuit between the battery and the starter motor for a high resistance. Did you find and 

correct the condition? If yes, go to step 8 . If no, go to next step.  

6. Inspect for poor connections at the starter. Did you find and correct the condition? If yes, go to step 8 . If 

no, go to next step.  

7. Replace the Starter. Refer to STARTER MOTOR REPLACEMENT . After replacement, go to next 

step.  

8. Operate the system for which the symptom occurred. Did you correct the condition? If yes, system OK. If 

no, go to step 2 .  

ENGINE CRANKS SLOWLY 

Perform the following checks:  

z

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

z

Wiring - Inspect the wiring for damage. Inspect all connections to the starter motor, solenoid, battery, and 
all ground connections.  

z

Engine - Make sure the engine is not seized. Refer to Symptoms in Engine Mechanical.  

 

2004 Hummer H2 

2004 STARTING & CHARGING SYSTEMS Starters - H2