Hummer H2. Manual — part 46

Conditions for Updating I/M System Status

Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported
by a Diagnostic Trouble Code (DTC). A system monitor is complete when either all of the DTCs comprising
the monitor have run and passed, or any one of the DTCs comprising the monitor have illuminated the MIL.
Once all of the tests are completed, the I/M System Status display will indicate YES in the COMPLETED
column. For example, when the HO2S Heater Test indicates YES, all of the oxygen sensor heaters have been
diagnosed. If the vehicle has four heated oxygen sensors, all four heater circuits have been diagnosed. The I/M
System Status will indicate NO under the Completed column when any of the required tests for that system
have not run. The following is a list of conditions that would set the I/M system status indicator to NO:

z

The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to
complete the tests.

z

The battery has been disconnected or discharged below operating voltage.

z

The control module power or ground has been interrupted.

z

The control module has been reprogrammed.

z

The control module DTCs have been cleared as part of a service procedure.

Monitored Emission Control Systems

The OBD-II System monitors all emission control systems that are on-board. Not all vehicles have a full
complement of emission control systems. For example, a vehicle may not be equipped with secondary Air
Injection (AIR) or Exhaust Gas Recirculation (EGR). The OBD-II regulations require monitoring of the
following:

z

Air conditioning system.

z

Catalytic converter efficiency.

z

Comprehensive component monitoring. Emission related inputs and outputs.

z

Evaporative (EVAP) emissions system.

z

Exhaust Gas Recirculation (EGR) system.

z

Fuel delivery system.

z

Heated catalyst monitoring.

z

Misfire monitoring.

z

Oxygen Sensor system (O2S or HO2S).

z

Oxygen sensor heater system (HO2S heater).

z

Secondary Air Injection (AIR) system.

Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list.
These tests run continuously on some vehicles and may not require an indicator.

Drive Cycle

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

Fig. 2: Typical Drive Cycle (1996-2000 GM Vehicles - Except Metro, Prizm, Saturn & Tracker)
Courtesy of GENERAL MOTORS CORP.

DRIVE CYCLE (2001-2003 MODELS)

Description

The following procedure is designed to satisfy the enable criteria necessary to execute all of the I/M readiness
diagnostics, and complete the trips for those particular diagnostics. When all diagnostic tests are completed, the
I/M System Status indicators are set to YES. Perform this test when more than one or all of the I/M System
Status indicators are set to NO.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures
may prevent tests such as Heated Oxygen Sensor (HO2S) heater and Evaporative Emission (EVAP) system
from initiating. If a step is interrupted before completion, perform the remaining portion of the set procedures.
Any portion of the set procedure that requires the engine at operating temperature may be repeated. This allows
most of the diagnostics to run and the remaining tests can be performed using the individual System Set
Procedures.

If the vehicle has recently run, start the Drive Cycle Procedure at step 3. This will allow the tests that require the
engine at operating temperature to run. Using this method allows shorter cool down periods if the tests requiring
a cold start do not initiate.

The scan tool can be used to monitor each of the I/M System Status indicators during the Drive Cycle
Procedure. When all of the indicators for a test step have updated to YES, testing can move on to the next step
even if the remaining portion of the test is not complete. For example, step 3 is designed to run the Evaporative
Emission (EVAP), Secondary Air Injection (AIR), and Heated Oxygen Sensor (HO2S) tests. The procedure
instructs the technician to operate the vehicle in the enable conditions for 6 minutes. If all 3 tests have updated
to YES within 4 minutes, it is not necessary to continue with the enable conditions and testing can advance to

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

the next step.

Enable Conditions

z

Barometric Pressure (BARO) is greater than 74 kPa.

z

Engine Coolant Temperature (ECT) is less than 75°F (24°C).

z

Intake Air Temperature (IAT) is less than 75°F (24°C).

z

The difference between the IAT and the ECT is 11°F (6°C) or less.

z

The battery voltage is 9-18 volts.

z

The fuel level is between 1/4 and 3/4.

Inspection/Maintenance (I/M) System Check

Any DTCs set may prevent the required monitors from running. In most cases, anytime a control module is
reprogrammed or the DTCs are cleared as part of a repair procedure, all the I/M system status indicators will
reset to NO. Prior to performing Drive Cycle Procedure (Inspection/Maintenance Complete System Set
Procedure), perform Inspection/Maintenance System Check. See Fig. 3 .

NOTE:

It may not be necessary to meet all conditions below to enable specific
monitors to run an individual diagnostic test. For more information on enable
conditions for running specific monitors, see SELF DIAGNOSTIC SYSTEM in
appropriate SELF DIAGNOSTICS article.

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

Fig. 3: Inspection/Maintenance System Check (2001-2003 GM Vehicles - Except Metro, Prizm, Saturn &
Tracker)
Courtesy of GENERAL MOTORS CORP.

Inspection/Maintenance (I/M) Complete System Set Procedure

The step numbers below refer to the step numbers in Fig. 4 on 2001-2003 GM vehicles, except Metro, Prizm,
Saturn & Tracker.

1. Ensure you perform INSPECTION/MAINTENANCE (I/M) SYSTEM CHECK before performing this

test. Failure to do so may result in difficulty updating the status to YES.

2. This step is to run the HO2S Heater Tests and initiate the EVAP System Test. Preprogramming the scan

tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.
The Engine Control Module (ECM) considers the engine to be cold if the following conditions are met:
ECT less than 95°F (35°C), ECT and IAT are within 11°F (6°C) of each other at start up.

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors