Hummer H1 (2006+). Manual - part 42

OBD-12

On-Board Diagnostics

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The engine control module (ECM) uses the accelerator pedal position (APP) sensors to control fuel delivery as requested by the
driver. Three APP sensors are located in a module at the base of the accelerator pedal. APP 2 should read approximately 4.5 volts
at idle and should steadily decrease to approximately 1 volts at WOT.

APP 3 - Range 0-5 Volts

The engine control module (ECM) used the accelerator pedal position sensor in order to control the fuel delivery as requested by
the driver. Three APP sensors are located in a module at the base of the accelerator pedal. APP 3 should read approximately 2.5
volts at WOT.

BARO - Range 10-105 kPa

The barometric pressure reading is determined form the boost sensor at ignition “ON”, engine “OFF”. The BARO reading display
represents barometric pressure and it is used to compensate for altitude differences.

Brake switch - Range Open/Closed

Is used for stop light and a redundant cruise control disengagement switch.

Boost Pressure - Range Open/Closed

The amount of turbo boost pressure in the intake manifold.This is measured in kPa and volts. True boost pressure is determined by
subtracting the barometric pressure from the actual reading.

Crank Reference Missed - Range 0-8

The scan tool will display the numbers of crank pulses missed. At idle, the crank reference missed range should be 0.

Cruise Active - Range ON/OFF

Indicates if the vehicle is in cruise control.

Cruise Brake Switch _ Range Open/Closed

When the brake pedal is applied, the switch sends a signal to the engine control module to disengage the cruise.

Cruise Switch - Range ON/OFF

Indicates if the cruise switch on the turn signal lever is in the “ON” position.

Desired Idle - Range 0-3187 RPM

The idle speed that is requested by the ECM. The ECM will compensate for various engine loads based on engine coolant temper-
ature to keep the engine at the desired speed.

Des. Inj Timing - Range 0-25˚

The amount of injection timing requested by the ECM.

DTC Sent this ignition – Range #

Indicates the total number of current DTCs set this ignition cycle.

ECT - Range -40 to +151˚C (-40 to 304˚F)

The engine coolant temperature (ECT) sensor sends a signal to the ECM relative to the engine coolant temperature. The sensor is a
thermistor which changes internal resistance as temperature changes. When the sensor is cold and the internal resistance is high,
the ECM monitors and interprets a high signal voltage as a cold engine. As the sensor warms and the internal resistance decreases,
the voltage signal will decrease and the ECM will interpret the lower voltage as a warm engine.

Engine Load _ Range 0-100 Percent

The amount of load on the engine.

Engine Run Time - Range 00:00:00 (HRS/MIN/SEC)

A measure of how long the engine has been operating. When the ignition is cycled to “OFF”, the value is reset to zero.

Engine Shut-Off Solenoid - Range ON/OFF

The engine shout-off solenoid (ESO) is located on the fuel injecting pump. When the ignition switch is “OFF”, the ESO is in the
NO FUEL position. The ESO prevents fuel from entering the fuel injection pump.

Engine Torque - Range 0-999 lb-ft

The amount of engine torque.

Engine Speed - Range 0-9999 RPM

The engine speed is computed by the ECM from the crankshaft position sensor (CKP). If the CKP is inoperative, an RPM reading
is taken from the injection pump cam signal. The RPM reading should remain closed to the desired idle during various engine loads
with engine idling. The engine speed value is very accurate.

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On-Board Diagnostics OBD-13

5745804

Fuel Rate - Range 0-80 mm3

This reading is displayed in millimeters cubed (MM3). This is the amount of fuel the ECM is requesting.

Fuel Temperature - Range -28 to +140˚C (-18 to +285˚F)

There is a thermistor located in the optical sensor that determines fuel temperature. When the sensor is cold and the internal resis-
tance is high, the ECM will interpret the low voltage as warm fuel.

Glow Plug - Range 0-25.5 volts

The amount of voltage applied to the glow plug system. The scan tool can be used to indicate if the glow plugs actually turn on by
monitoring the voltage drop. Also, a good functional check of the glow plug relay.

Glow Plug System - Range Enabled/Disabled

Indicates whether or not the ECM has requested the glow plugs be turned on.

IAT - Range -40 to +151˚C (-40 to +304˚)

The intake air temperature sensor sends a signal to the ECM relative to the incoming air. The IAT is used by the ECM to adjust the
fuel delivery.

Ignition volts - Range 0-25.5 Volts

This represents the system voltage measured by the ECM at its ignition feed circuit Ignition voltage is only present when the vehi-
cle is running.

Inj. Pump Cam Reference Missed - 0-8

The Tech 2 will display the number of cam pulses missed. At idle, the inj. pump cam reference missed. At idle, the inj.pump cam
reference Missed range should read 0.

Inj. Pump Sol. Closure Time - Range 0.0-4.0 milliseconds.

Indicates the amount of time the fuel solenoid takes to close. When engine lode is increased, the closure time will fluctuate.

Lift Pump - Range 0.0-25.5 Volts

The amount of voltage the lift pump system is drawing. Also, a good functional check of the lift pump relay and the oil pressure
switch.

MIL - Range ON/OFF

Represents the commanded state of the Service Engine Soon Light

Number or DTCs - Range #

Indicates the total number of current DTCs set, but does not necessarily mean that the MIL is illuminated.

Resume Switch - Range ON/OFF

Indicates if the cruise control resume switch is activated. The scan tool may be used in order to determine if the cruise control re-
sume set switch is functioning properly.

Service Throttle Soon Lamp - Range ON/OFF

Represents the commanded state of the service throttle soon lamp.

Set Switch - Range ON/OFF

Indicates if the cruise control set switch is activated. The scan tool may be used to dete4rmine if the cruise control set switch is
functioning properly.

Startup Cooling - Range -40 to +151˚C (-40 to +304˚F)

A reading of the vehicles coolant temperature at start-up. This will change with every key cycle.

TDC Offset - Range -2.50 to +2.50˚

The ECM has the ability to determine the amount of offset that is needed to bring the engine to top dead center.This is used by the
ECM in order to determine the proper injection timing and the fuel delivery. This value may be displayed as a positive or negative
number.

Trans. Fluid Temp. - Range -40 to 151˚C (-40 to 304˚F)

This value represents the input signal of the transmission fluid temperature sensor.

Vehicle Speed - Range 0-98

Vehicle speed is a ECM internal parameter. The vehicle speed is computed by timing pulses coming from the vehicle speed sensor.
Vehicle speed is used to check the torque converter clutch lock-up speed or speedometer accuracy. the speed is displayed in both
kilometers per hour and miles per hour.

OBD-14

On-Board Diagnostics

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Wastegate Solenoid - Range 0-100 Percent

The ECM cycles the boost solenoid ON and OFF. The on time, or duty cycle, of the solenoid valve is expressed as a percent. The
boost solenoid meters the vacuum level at the wastegate valve actuator as commanded by the ECM.

No Malfunction Indicator Lamp (MIL) “Check Engine”

Step

Action

Value(s)

Yes

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to step 2.

Go to OBD system

check.

Attempt to start the engine.
Does the engine start?

—

Go to step 3.

Go to step 6.

Check the fuse number 4B of the interior fuse box.
Is the fuse OK?

—

Go to step 4.

Go to step 14.

Turn the ignition “ON,” probe the ignition feed circuit at
the cluster connector with a test light to ground.
Is the test light “ON?”

—

Go to step 5.

Go to step 11.

Turn the ignition “OFF.”

Disconnect the black ECM connector.

Turn the ignition “ON.”

Connect a fused jumper to the MIL control circuit at
the ECM connector.

Observe the MIL.

Is the MIL “ON?”

—

Go to step 9.

Go to step 10.

Check the ECM ignition Feed and Battery Feed fuses.
Are both of the fuses OK?

—

Go to step 7.

Go to step 13.

Turn the ignition “OFF.”

Disconnect the ECM connectors.

Turn the ignition “ON.”

Probe the ECM harness ignition and battery feed
circuits with a test light to ground.

Is the test light “ON” both circuit?

—

Go to step 8.

Go to step 12.

Check for a faulty ECM ground or a poor ECM
ground connection.

If a problem is found, repair as necessary.

Was a problem found?

—

Go to step 18.

Go to step 9.

Check for a poor connection at the ECM.

If a poor connection is found, repair as necessary.

Was a problem found?

—

Go to step 18.

Go to step 15.

Check the MIL control circuit for an open.

If the MIL control circuit is open, repair as
necessary.

Was a problem found?

—

Go to step 18.

Go to step 16.

Repair open in the ignition feed circuit to connector C3.
Is the action complete?

—

Go to step 18.

—

Locate and repair open in the ECM battery feed circuit
or the ECM ignition feed circuit as necessary.
Is the action complete?

—

Go to step 18.

—

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On-Board Diagnostics OBD-15

5745804

Locate and repair short to ground in the ECM Ignition
Feed circuit or the ECM Battery Feed circuit as neces-
sary.
Is the action complete?

—

Go to step 18.

—

Locate and repair short to ground in the volt/oil module
Ignition Feed circuit.
Is the action complete?

—

Go to step 18.

—

Replace the ECM.

NOTE: If the ECM is faulty, then ECM must be pro-
grammed. Go to ECM Replacement and Programming
Procedures.

Is the action complete?

—

Go to step 18.

—

Check the MIL control circuit for a poor connection
at the volt/oil module connector.

If a problem is found, repair as necessary.

Was a problem found?

—

Go to step 18.

Go to step 17.

Replace the Volt/Oil module.
Is the action complete?

—

Go to step 18.

—

Using the Scan Tool, select “DTC,” “Clear Info.”

Attempt to start the engine.

Does the engine start and continue to run?

—

Go to Step 19

Go to step 2.

Allow engine to idle until normal operating temper-
ature is reached.

Select “DTC,” “Failed This Ign.”

Are any DTCs displayed?

—

Go to Applicable

DTC Table

Go to step 20.

Using the Scan Tool, select “Capture Info,”
“Review Info.”
Are any DTCs displayed that have not been diagnosed?

—

Go to Applicable

DTC Table

System OK

No Scan Tool Data

Step

Action

Value(s)

Yes

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to step 2.

Go to OBD system

check.

Ignition “OFF” for 30 seconds.

Ignition “ON,” Engine “OFF.”

Is the MIL “ON”?

—

Go to step 3.

Go to Chart A-1.

Can the Scan Tool communicate with the ECM?

—

Go to step 4.

Go to step 7.

With the Scan Tool, command the MIL “ON” and
“OFF.”

—

Go to step 17.

Go to step 5.

No Malfunction Indicator Lamp (MIL) “Check Engine”

Step

Action

Value(s)

Yes

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