Hummer H2. Manual — part 762

DTC C0121

Circuit Description

The solenoid valve relay supplies power to the solenoid valve coils in the EBCM. The solenoid valve relay,
located in the EBCM, is activated whenever the ignition switch is in the RUN position and no faults are present.
The solenoid valve relay remains engaged until the ignition is turned OFF or a failure is detected.

Conditions for Running the DTC

The ignition switch is in the ON position.

Conditions for Setting the DTC

z

DTC C0121 will set anytime the solenoid valve relay is commanded on and the EBCM does not see
battery voltage at the solenoid valves.

z

DTC C0121 will set anytime the EBCM commands the solenoid valve relay off and battery voltage is still
present at the solenoid valves.

Action Taken When the DTC Sets

If equipped, the following actions occur:

z

The EBCM disables the ABS/TCS/DRP for the duration of the ignition cycle.

z

A malfunction DTC is set.

z

The ABS indicator turns ON.

z

The TRAC Off indicator turns ON.

z

The Red BRAKE Warning indicator could turn on.

Conditions for Clearing the DTC

z

The condition for the DTC is no longer present and the DTC is cleared with a scan tool.

z

The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC
is not detected in 100 consecutive drive cycles.

Diagnostic Aids

z

It is very important that a thorough inspection of the wiring and connectors be performed. Failure to

Did you complete the repair?

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

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2

carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement
with reappearance of the malfunction.

z

Thoroughly inspect any circuitry that may be causing the complaint for the following conditions:

{

Backed out terminals

{

Improper mating

{

Broken locks

{

Improperly formed or damaged terminals

{

Poor terminal-to-wiring connections

{

Physical damage to the wiring harness

z

The following conditions may cause an intermittent malfunction:

{

A poor connection

{

Rubbed-through wire insulation

{

A broken wire inside the insulation

z

If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor
Connections in Wiring Systems.

z

The solenoid valve relay is an integral part of the EBCM and is not serviced separately.

Test Description

The number below refers to step number on the diagnostic table.

2: This step determines if the DTC is current.

DTC C0121

Step

Action

Yes

No

Schematic Reference: ABS Schematics
Connector End View Reference:ABS Connector End Views

1

Did you perform the Diagnostic System Check?

Go to

Step 2

Go to Diagnostic

System Check -

ABS

2

1. Install a scan tool.

2. Turn ON the ignition, with the engine OFF.

3. Use the scan tool in order to clear the DTCs.

Does the DTC reset?

Go to

Step 3

Go to Diagnostic

Aids

3

1. Connect the J 39700 universal pinout box using the. See

Special Tools and Equipment . J 39700-530 cable adapter to
the EBCM harness connector only.

2. Test the battery positive voltage circuit for an open, high

resistance, or a short to ground. Refer to Circuit Testing and
Wiring Repairs in Wiring Systems.

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2

DTC C0161

Circuit Description

The stoplamp switch is a normally open switch, when the brake pedal is depressed the EBCM will sense battery
voltage. This allows the EBCM to determine the state of the brake lamps. The EBCM sources 5 volts on the
stop lamp switch signal circuit when the stop lamp switch is inactive. The voltage is supplied a ground path
through the stop lamp bulbs.

Conditions for Running the DTC

The ignition switch is ON.

Conditions for Setting the DTC

z

EBCM detects open in the brake signal circuit.

z

Both brake lamps are faulty.

z

The stoplamp switch input voltage is between 6.6 and 9 volts for 0.5 second.

Action Taken When the DTC Sets

If equipped, the following actions occur:

z

A malfunction DTC will set.

z

The EBCM stores this information-only DTC for as long as the condition is present.

z

The ABS remains functional.

z

The ABS indicator remains OFF.

Conditions for Clearing the DTC

z

The condition for the DTC is no longer present and the DTC is cleared with a scan tool.

z

The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC
is not detected in 100 consecutive drive cycles.

Did you find and correct the condition?

Go to

Step 5

Go to Step 4

4

Replace the Electronic Brake Control Module (EBCM). Refer to
Electronic Brake Control Module Replacement .
Did you complete the replacement?

Go to

Step 5

-

5

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

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2

Diagnostic Aids

z

It is very important that a thorough inspection of the wiring and connectors be performed. Failure to
carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement
with reappearance of the malfunction.

z

Thoroughly inspect any circuitry that may be causing the complaint for the following conditions:

{

Backed out terminals

{

Improper mating

{

Broken locks

{

Improperly formed or damaged terminals

{

Poor terminal-to-wiring connections

{

Physical damage to the wiring harness

z

Possible causes of this DTC are the following conditions:

{

A signal circuit of the stop lamp switch is open

{

The stop lamp switch is misadjusted

{

Verify proper stop lamp switch operation using the data list of the scan tool. As the brake is
applied, the data list displays the stop lamp switch ON within 2.54 cm (1 in) of travel

{

All brake lamps are open

{

All brake lamp grounds are open

{

Circuit has a wiring problem, terminal corrosion, or poor connections

{

Loose or corroded EBCM ground

z

If an intermittent malfunction exists refer to Testing for Intermittent Conditions and Poor
Connections in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

3: This DTC detects an open stop lamp switch signal circuit from the stop lamp side of the splice pack to
the EBCM.

4: The EBCM sources 5 volts on the stop lamp switch signal circuit. This small voltage has a ground path
through the stop lamp bulbs. This DTC sets if the path to ground is open.

DTC C0161

Step

Action

Yes

No

Schematic Reference: ABS Schematics
Connector End View Reference: ABS Connector End Views or Lighting Systems Connector End
Views in Lighting Systems

1

Did you perform the ABS Diagnostic System Check?

Go to

Step 2

Go to Diagnostic

System Check -

ABS

1. Press the brake pedal.

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2