Experiencing issues with your GMC 2019 Sierra passing its emissions test? You’re not alone. Many Sierra owners encounter situations where their vehicle fails due to “incomplete” OBD2 monitors. This often happens after a battery disconnection or when the vehicle isn’t driven regularly. Understanding Gmc 2019 Sierra Obd2 Codes and how to address readiness monitor issues is crucial for getting your truck back on the road legally.
Understanding OBD2 Readiness Monitors in Your GMC Sierra
OBD2 (On-Board Diagnostics II) monitors are self-tests your GMC Sierra’s computer performs to ensure all emission control systems are functioning correctly. These monitors, such as the Evaporative System, Fuel System, and Oxygen Sensor monitors, need to be in a “ready” state to pass an emissions or smog check. If these monitors are “not ready” or “incomplete,” it indicates that the system hasn’t completed its self-test cycle, often resulting in a failed inspection.
Several factors can cause OBD2 monitors to be incomplete on your 2019 GMC Sierra:
- Battery Disconnection: Disconnecting or replacing your battery resets the vehicle’s computer and clears the readiness monitor status.
- Recent Diagnostic Code Clearing: If you’ve recently cleared any diagnostic trouble codes (DTCs) using an OBD2 scanner, the monitors will reset to “not ready.”
- Intermittent Driving Patterns: Vehicles driven infrequently or only for short trips may not provide the conditions necessary for all monitors to complete their self-tests.
When these monitors are not ready, your GMC 2019 Sierra might still run perfectly fine, but it won’t pass an emissions test. The key to resolving this issue and getting those monitors to a “ready” state is often performing a “drive cycle.”
The GMC Sierra Drive Cycle: Resetting Your OBD2 Monitors
A “drive cycle” is a specific sequence of driving conditions designed to allow your GMC Sierra’s computer to run all the necessary self-tests and set the OBD2 monitors to “ready.” Here’s a step-by-step guide based on the procedure for GM vehicles, tailored for your 2019 GMC Sierra:
Before You Begin:
- Cold Start: Ensure your Sierra has been off for at least one hour. The engine coolant temperature should be below 122°F (50°C) and close to the ambient air temperature.
- Fuel Level: Maintain a fuel tank level between 1/4 and 3/4 full. This is particularly important for the Evaporative System monitor to run.
Drive Cycle Steps:
A. Cold Start: Begin with a cold start. Do not turn the key to the “ON” position before starting, as this might prevent the Oxygen Sensor (O2) diagnostic from running.
B. Idle: Start the engine and let it idle for 2.5 minutes. Turn on the air conditioner and rear defroster during this idle period. This initiates tests for the Oxygen Sensor Heater, Air Injection System, EVAP Purge (No Flow), and Misfire Detection.
C. Acceleration: Turn off the air conditioner and rear defroster. Accelerate smoothly at half throttle until you reach 55 mph. This step activates self-tests for Misfire Detection, Fuel Trim, and EVAP Purge Flow.
D. Steady Speed (Part 1): Maintain a steady speed of 55 mph for three minutes. During this phase, the system checks Oxygen Sensor response, Air Intrusion (AIS System), EGR Flow, Purge Valve, Misfire Detection, and Fuel Trim.
E. Deceleration: Gradually release the accelerator pedal and coast down to 20 mph without braking or shifting gears. This allows the ECU to test the EGR System, EVAP Purge System, and Long Term Fuel Trims again.
F. Acceleration (Part 2): Accelerate again at 3/4 throttle until you reach 55-60 mph. This repeats the same self-tests performed in step C.
G. Steady Speed (Part 2): Hold a steady speed of 55 mph for five minutes. This extended steady speed allows the Catalyst monitor diagnostics to run, in addition to the tests from step D. If your catalytic converter is marginal or the battery was recently disconnected, it might take up to five drive cycles to complete the Catalyst Monitor.
H. Deceleration (Part 2): Coast down to 20 mph again, similar to step E, without using brakes or shifting. This repeats the diagnostics from step E.
Image of drive cycle steps as a list.
Performing this GMC Sierra drive cycle once or twice is often sufficient to reset the Oxygen Sensor and Fuel System monitors. The Evaporative System monitor might require a couple of drive cycles and ensuring the fuel tank is within the 1/4 to 3/4 range.
Common GMC 2019 Sierra OBD2 Codes Related to Monitor Readiness
While “incomplete monitor” itself isn’t an OBD2 code, you might encounter codes that indicate issues preventing monitors from setting. Some common codes related to emissions and monitor readiness in GMC Sierra vehicles include:
- P0440, P0442, P0455: Evaporative Emission Control System faults (often related to the fuel cap or leaks in the EVAP system).
- P0131, P0134, P0137: Oxygen Sensor circuit issues (related to sensor malfunction or wiring problems).
- P0171, P0174: System Too Lean (Bank 1 & Bank 2) – can affect fuel system monitor readiness.
If you encounter specific OBD2 codes along with incomplete monitors, it’s advisable to address the underlying issue causing the code before attempting the drive cycle. An OBD2 scanner can be invaluable for reading and clearing codes.
Conclusion: Getting Your GMC Sierra Ready for Inspection
Dealing with incomplete OBD2 monitors on your GMC 2019 Sierra can be frustrating, especially when it prevents you from passing your emissions test. However, understanding the drive cycle procedure and the importance of readiness monitors empowers you to take control. By carefully following the outlined drive cycle, you can often reset these monitors yourself and ensure your GMC Sierra is ready for its next inspection. Remember to always prioritize safe driving practices while performing a drive cycle. If issues persist, consulting a certified mechanic is always a wise step to diagnose and resolve any underlying problems affecting your vehicle’s emissions system.
