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