Hummer H2. Manual — part 1091

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

Follow these instructions in order to avoid an incorrect diagnosis because of connections:

z

If testing the vehicle with the battery cables still connected, wiggle the J 42000 clips on the terminal bolt.
This may cut through any coating or through any oxidation that may be present on the bolt. See Special
Tools and Equipment .

Even new bolts contain a protective coating that may insulate or cause a resistance in the test circuit.

z

If correct connections to the battery terminal bolts in the vehicle are in doubt, perform the following
steps:

1. Disconnect the negative battery cable.

2. Disconnect the positive battery cable.

3. Install the test adapters on the terminals.

4. Follow the instructions for testing a removed battery.

z

If the tester displays a REPLACE BATTERY or BAD CELL-REPLACE result for a battery tested in the
vehicle with the battery cables connected, perform the following steps:

1. Disconnect the negative battery cable.

2. Disconnect the positive battery cable.

3. Install the tester adapters.

4. Follow the instructions for testing a removed battery.

5. Replace the battery only if the second test shows a REPLACE BATTERY or BAD CELL-

REPLACE result.

Use the test code from the second test for any warranty purposes.

z

Use the correct terminal adapters.

Do not use any common bolts or a combination of bolts, of nuts, and of washers as adapters when testing
the battery.

connections to the battery terminals. A failure to obtain the correct
connections during the test may result in a failed test on a good battery.
See Special Tools and Equipment .

z

Use the Out of Vehicle test for each battery when testing a vehicle with
dual batteries.

IMPORTANT: Always write the test code displayed by the tester on the repair order

for any warranty purposes. The number is a unique code that
describes the test data for a particular battery at a particular time.
The test code may occasionally repeat when you retest the same
battery. More often, each test will result in a different code. Use the
test code from the second, or Out of Vehicle test.

2004 Hummer H2

2004 ELECTRICAL Engine Electrical - Hummer H2