Hummer H2. Manual - part 1119

DTC P0622 

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 0 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 will set. When the DTC sets, the PCM will send a class 2 serial data message to the IPC to illuminate the 
charge indicator. 

or  

Conditions for Running the DTC 

Key ON Test 

z

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

z

The key is in the RUN position.  

z

The engine is not running.  

Run Test 

Replace the PCM. Refer to Powertrain Control 
Module (PCM) Replacement in Engine 
Controls.Did you complete the replacement?

Go to Step 11

-

11

1. Review and record the scan tool Fail 

Records data.  

2. Use the scan tool in order to clear the 

DTC.  

3. Operate the vehicle within the Conditions 

for Running the DTC as specified in the 
supporting text.  

4. 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?

Go to Step 2

System OK

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2

  

z

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

z

The engine is less than 3000 RPM.  

Conditions for Setting the DTC 

z

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

z

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 

z

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

z

The malfunction indicator lamp (MIL) will not illuminate.  

Conditions for Clearing the DTC 

z

The Conditions for Setting the DTC are no longer present.  

z

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

z

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

DTC P0622 

Step

Action

Value

(s)

Yes

No

Schematic Reference:Starting and Charging Schematics 
Connector End View Reference: Engine Electrical Connector End Views

1

Did you perform the Engine Electrical 
Diagnostic System Check?

-

Go to Step 2

Go to Diagnostic 

System Check - 

Engine Electrical

2

1. Install a scan tool.  

2. Start the engine.  

3. With a scan tool, observe the GEN 

- F Terminal parameter in the PCM 
data list.  

Does the scan tool indicate that the GEN 
- F Terminal parameter is within the 
specified range?

5-95%

Go to Step 3

Go to Step 4

3

With the scan tool command the 
generator OFF. 
Does the GEN - F Terminal equal the 
specified value?

0%

Go to Testing for 

Intermittent Conditions 

and Poor Connections in 

Wiring Systems

Go to Step 4

1. Turn OFF the ignition.  

2. Disconnect the generator 

connector.  

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2

  

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 

4

3. Connect test lamp to battery 

positive voltage.  

4. Turn ON the ignition, with the 

engine OFF.  

5. Probe the F-Terminal in the 

generator connector.  

6. Observe the GEN - F Terminal 

Signal parameter in the PCM data 
list.  

Is the GEN - F Terminal Signal 
parameter near the specified value?

100%

Go to Charging System 

Test (CS/AD/SI 

Generators)

Go to Step 5

5

Test the generator field duty cycle signal 
circuit for a short or open. Refer to 
Circuit Testing and Wiring Repairs in 
Wiring Systems. 
Did you find and correct the condition?

-

Go to Step 8

Go to Step 6

6

Inspect for poor connections at the 
harness connector of the PCM. Refer to 
Connector Repairs in Wiring Systems. 
Did you find and correct the condition?

-

Go to Step 8

Go to Step 7

7

Replace the PCM. Refer to Powertrain 
Control Module (PCM) Replacement 
in Engine Controls - 4.8L, 5.3L or 6.0L. 
Did you complete the repair?

-

Go to Step 8

-

8

1. Review and record the scan tool 

Fail Records data.  

2. Clear any DTCs.  

3. Operate the vehicle within the Fail 

Records conditions as noted.  

4. Using a scan tool, monitor the 

Specific DTC info for this DTC.  

Does the scan tool indicate that this DTC 
failed this ignition?

-

Go to Step 2

System OK

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2

  

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 

z

The ignition is ON.  

z

System voltage between 9.0-18.0 volts.  

Conditions for Setting the DTC 

z

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

z

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 only. This information 
will not be stored as Freeze Frame Records. 

Conditions for Clearing the MIL/DTC 

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.  

DTC P1637 

Step

Action

Value

Yes

No

Schematic Reference:Starting and Charging Schematics 
Connector End View Reference:Engine Electrical Connector End Views

1

Did you perform the Engine Electrical 
Diagnostic System Check?

-

Go to Step 2

Go to Diagnostic 

System Check - 

Engine Electrical

2

1. Install a scan tool.  

2. Start the engine.  

3. With a scan tool, monitor the DTC 

information for DTC P1637 in Engine 
Controls.  

Does the scan tool indicate that DTC P1637 
has passed?

-

Go to Testing for 

Intermittent 

Conditions and Poor 

Connections in Wiring 

Systems

Go to Step 3

1. Turn ON the ignition, leaving the 

 

2004 Hummer H2 

2004 ELECTRICAL Engine Electrical - Hummer H2