Hummer H2. Manual — part 1161

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

SYMPTOMS - ENGINE ELECTRICAL

z

Perform Diagnostic System Check - Engine Electrical before using the Symptom Tables in order to

3

engine OFF.

2. Disconnect the generator harness

connector.

3. Measure the voltage between the

generator turn on signal circuit and
ground.

Does the voltage measure near the specified
value?

10-11

volts

Go to Step 5

Go to Step 4

4

Test the generator turn on 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

5

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

-

Go to Step 8

Go to Charging

System Test

(CS/AD/SI

Generators)

6

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

-

Go to Step 8

Go to Step 7

7

Replace the PCM/ECM. Refer to
Powertrain Control Module (PCM)
Replacement in Engine Controls 4.8L,
5.3L, and 6.0L.Is action complete?

IMPORTANT:

The replacement PCM must be
programmed.

-

Go to Step 8

-

8

1. Use the scan tool in order to clear the

DTCs.

2. Operate the vehicle within the

Conditions for Running the DTC as
specified in the supporting text.

Does the DTC reset?

-

Go to Step 2

System OK

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

2004 Hummer H2

2004 ELECTRICAL Engine Electrical - Hummer H2

verify that all of the following are true:

{

There are no DTCs set.

{

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:

{

Battery Description and Operation

{

Starting System Description and Operation

{

Charging System Description and Operation

Visual/Physical Inspection

z

Inspect for aftermarket devices which could affect the operation of the Starting and Charging Systems.
Refer to Checking Aftermarket Accessories in Wiring 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. Refer to Testing for
Intermittent Conditions 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

z

Starter Solenoid Clicks, Engine Does Not Crank

z

Engine Cranks Slowly

z

Battery Inspection/Test (Non-HP2)

z

Charge Indicator Always On

z

Charge Indicator Inoperative

z

Charging System Test (CS/AD/SI Generators)

z

Generator Noise Diagnosis

BATTERY INSPECTION/TEST (NON-HP2)

Diagnostic Aids

CAUTION: Refer to Battery Disconnect Caution in Cautions and Notices.

IMPORTANT:

z

The battery test using the J 42000 Battery Tester requires correct

2004 Hummer H2

2004 ELECTRICAL Engine Electrical - Hummer H2