Ensuring your 2005 GMC Sierra passes its emissions test is crucial, and understanding your OBD2 readiness monitors is a key part of this process. These monitors are diagnostic tests your vehicle runs to ensure all emission control systems are functioning correctly. If these monitors are not set, your Sierra might fail an inspection, even if there are no obvious problems. This guide will walk you through the complete system set procedure to ensure your 2005 GMC Sierra’s OBD2 readiness monitors are in the “ready” state, using the official General Motors Inspection/Maintenance (I/M) complete system set procedure.
Understanding OBD2 Readiness Monitors on Your 2005 GMC Sierra
OBD2 (On-Board Diagnostics II) systems are standard on all cars sold in the US from 1996 onwards, including your 2005 GMC Sierra. Readiness monitors are a set of self-tests that the vehicle’s computer performs to verify that the emission control systems are working as they should. These systems include components like the oxygen sensors, catalytic converter, evaporative emissions (EVAP) system, and more. When a monitor is “ready,” it means the test has been completed and passed. If a monitor is “not ready,” it indicates that the test hasn’t been fully run, which can happen after a battery disconnect or recent repairs.
For emissions testing, most areas require all or all but one of your readiness monitors to be in a “ready” state. If too many monitors are “not ready,” your 2005 GMC Sierra will likely fail the test. The procedure outlined below is designed to set all of these monitors to “ready” by fulfilling the necessary driving conditions and diagnostic criteria.
Conditions for Starting the I/M System Set Procedure on Your 2005 GMC Sierra
Before you begin the system set procedure, ensure your 2005 GMC Sierra meets the following “cold start” conditions. These conditions are vital for the diagnostic tests to run correctly:
- Voltage: The battery voltage must be between 11 and 18 volts.
- Barometric Pressure (BARO): The barometric pressure must be greater than 75 kPa. This is generally not an issue unless you are at a very high altitude.
- Engine Coolant Temperature (ECT): At startup, the engine coolant temperature should be between 4-30°C (39-86°F).
- Intake Air Temperature (IAT): Similarly, the intake air temperature at startup should be between 4-30°C (39-86°F).
- Temperature Difference: The difference between the IAT and ECT should be less than or equal to 6°C (10.8°F).
- Ambient Air Temperature: The outside air temperature should also be between 4-30°C (39-86°F).
- Fuel Level: Your fuel tank should be between 15-85 percent full.
- Fuel Alcohol Content:
- For Sierras without RPO LMG (engine code): Fuel alcohol content must be less than 15 percent.
- For Sierras with RPO LMG: Fuel alcohol content must be less than 87 percent.
Meeting these cold start conditions ensures that the engine control module (ECM) can accurately run all the necessary diagnostic routines. Use a scan tool to check the I/M monitor enabled parameters to confirm these conditions are met before proceeding.
Step-by-Step Guide to Perform the 2005 GMC Sierra I/M System Set Procedure
Follow these steps precisely to perform the Inspection/Maintenance (I/M) System Set Procedure on your 2005 GMC Sierra. It is crucial to follow each step in order and under the specified conditions.
Important Preparation:
- Ensure all the “cold start” conditions listed above are met.
- Turn the ignition OFF for approximately 5 minutes to allow sensors to cool down before starting. Once started, do NOT turn off the engine until the procedure is complete, unless instructed otherwise.
- If the EVAP I/M System Status indicator showed “NO” previously, and if available, perform the EVAP Service bay test with a scan tool. If not available, understand it might take multiple drive cycles (up to 6) and extended time (up to 17 hours between cycles) for the EVAP monitor to set.
- If the O2S Heater System Status indicator is “NO”, ensure the ignition has been off for at least 10 hours prior to starting this procedure.
Procedure Steps:
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Parking Brake and Vehicle Position: Set the parking brake and ensure your 2005 GMC Sierra is in Park (automatic transmission) or Neutral (manual transmission).
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Turn Off Accessories: Switch off all accessories, including the HVAC system, headlights, radio, and any aftermarket electrical equipment. This minimizes electrical load during the test.
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Initial Idle: Start the engine and let it idle for at least 2 minutes, or until the engine coolant temperature reaches 65°C (149°F).
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Elevated Idle: Run the engine for 6.5 minutes under these conditions:
- Mass Air Flow (MAF) parameter between 4-30 g/s.
- Engine speed consistently between 1000-3000 RPM.
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Return to Idle: Let the engine return to idle for 1 minute.
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Drive in Gear (Simulated): Apply and hold the brake pedal, then shift to Drive (automatic) or depress the clutch pedal (manual). Operate the vehicle under these conditions for 2 minutes:
- Depress the accelerator pedal slightly until the Throttle Position (TP) Sensor angle is more than 2 percent.
- MAF signal between 15-30 g/s.
- RPM steady between 1200-2000 RPM.
Important: Do not touch the accelerator pedal during the idle periods unless instructed. Changes in throttle position or engine speed can invalidate the test.
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Return to Idle in Neutral/Park: Release the accelerator pedal, and shift to Park (automatic) or Neutral and release the clutch pedal (manual). Allow the engine to idle for 2 minutes.
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Rapid Throttle Depressions: Quickly depress the accelerator pedal until the TP Sensor Angle is more than 8 percent and then release it back to idle. Repeat this action 3 times.
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Idle Again: Allow the engine to idle for at least 2 minutes.
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Low Speed Drive: Release the parking brake and drive your 2005 GMC Sierra at 24 km/h (15 mph) or slower for 2 minutes.
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Highway Speed Drive: Continue driving for at least 5.5 miles at speeds between 45-112 km/h (28-70 mph), ensuring you reach at least 80 km/h (50 mph) at some point.
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Deceleration: Release the accelerator pedal for at least 2 seconds to allow the vehicle to enter decel fuel cut-off mode.
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Moderate Acceleration: Depress the accelerator pedal until the TP Sensor angle increases by 3-20 percent and maintain a safe speed for 1 minute.
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Final Idle in Drive/Neutral: Safely stop the vehicle. Keep the engine in Drive (automatic) or Neutral with the clutch pedal depressed and parking brake applied (manual). Idle for 2 minutes.
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Idle in Park/Neutral: Shift to Park (automatic) and apply the parking brake, or shift to Neutral and release the clutch pedal (manual).
Important: Do not disturb the vehicle or turn off the ignition until instructed. Any disturbance may invalidate the test.
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Ignition Off and Wait: Turn OFF the ignition and exit the vehicle. Do not disturb the vehicle for 45 minutes.
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Verify Monitor Status: After 45 minutes, observe the Inspection/Maintenance (I/M) System Status with a scan tool. All I/M System Status indicators should now display “YES.”
Troubleshooting and Further Assistance
- EVAP Monitor Not Ready: If the EVAP I/M System Status indicator still shows “NO,” turn the ignition OFF for 17 hours, ensure cold start conditions are met again, and repeat steps 12-18 up to six more times. If it remains “NO,” consult the Inspection/Maintenance (I/M) System DTC Table to identify Diagnostic Trouble Codes (DTCs) that did not run and follow the Conditions for Running the DTC to set the EVAP I/M System Status indicator.
- Other Monitors Not Ready: If any other I/M System Status indicators are “NO,” refer to the Inspection/Maintenance (I/M) System DTC Table for the specific indicator. This table will identify the DTCs associated with each monitor. Follow the Conditions for Running the DTC to address the specific issue and set the associated status indicator.
By following these steps carefully, you should be able to set the OBD2 readiness monitors on your 2005 GMC Sierra, ensuring it is ready for emissions testing. Remember to use a scan tool to monitor the process and verify the readiness status of each monitor. This detailed procedure ensures you address all the necessary conditions and steps to get your 2005 GMC Sierra compliant with emissions standards.
