OBD2 EVAP Monitor Not Ready: Understanding and Resetting Your GM Vehicle’s Emissions System

Is your OBD2 scanner showing the EVAP monitor as “Not Ready”? This can be a frustrating issue, especially when you need to pass an emissions test. For General Motors (GM) vehicles, this is a particularly common concern. The Evaporative Emission (EVAP) system monitor is known to be quite sensitive and can take multiple drive cycles to reset to a “Ready” status. This guide, tailored for GM car owners and enthusiasts, will break down the reasons behind an “Obd2 Evap Not Ready” status and provide a step-by-step procedure to help you reset it, based on the official GM Inspection/Maintenance (I/M) Complete System Set Procedure.

Understanding the EVAP System and Monitor

The EVAP system in your vehicle is designed to prevent fuel vapors from escaping into the atmosphere. It’s a crucial part of your car’s emissions control system. The OBD2 system monitors the EVAP system’s functionality to ensure it’s working correctly. When the EVAP monitor status is “Not Ready,” it means the system hasn’t completed its self-tests. This “Not Ready” status will often prevent you from passing vehicle emissions inspections, which are mandatory in many regions.

Why is My EVAP Monitor “Not Ready”?

Several factors can lead to an “EVAP Monitor Not Ready” status. Common reasons include:

• Recent Battery Disconnection: Disconnecting or replacing your car battery can reset many of the vehicle’s computer systems, including emissions monitors.
• Diagnostic Trouble Codes (DTCs) Cleared: If you’ve recently cleared any DTCs, even if they weren’t EVAP related, the monitors will reset and need to run their tests again.
• Recent Repairs: Work done on the engine or emissions system might necessitate the monitors to reset.
• Specific Driving Conditions Not Met: The EVAP monitor, like other OBD2 monitors, has specific “drive cycle” requirements – a set of driving conditions that must be met for the test to run and complete. GM vehicles, in particular, are known to have stringent and sometimes lengthy drive cycle requirements for the EVAP monitor.

The GM Inspection/Maintenance (I/M) Complete System Set Procedure for EVAP

Getting your GM EVAP monitor to “Ready” often involves performing a specific drive cycle. Below is the official GM procedure, which can help initiate and complete the EVAP system self-test. It’s important to follow these steps carefully.

Before You Begin: Cold Start Conditions

To ensure the procedure works correctly, you need to meet “cold start” conditions. This means the following criteria must be met when you start your vehicle:

• Voltage: Battery voltage between 11-18 volts.
• Barometric Pressure (BARO): Above 75 kPa.
• Engine Coolant Temperature (ECT): Between 4-30°C (39-86°F).
• Intake Air Temperature (IAT): Between 4-30°C (39-86°F).
• IAT and ECT Difference: Less than or equal to 6°C (10.8°F).
• Ambient Air Temperature: Between 4-30°C (39-86°F).
• Fuel Level: Between 15-85 percent.
• Fuel Alcohol Content:
  • Without RPO LMG: Less than 15 percent.
  • With RPO LMG: Less than 87 percent.

Step-by-Step GM EVAP Monitor Drive Cycle Procedure

Important: Before starting, ensure your vehicle meets all the cold start conditions listed above. Turn off the ignition for at least 5 minutes to allow sensors to cool down. Once started, do not turn off the engine until the procedure is complete.

1. Cold Start Verification: Confirm all cold start conditions are met. If your OBD2 scanner shows the EVAP monitor as “Not Ready,” and an EVAP service bay test is unavailable, understand it might take multiple drive cycles (up to 6, with up to 17 hours between each) for the monitor to become “Ready.” If the O2S Heater monitor is “Not Ready,” ensure the ignition has been off for at least 10 hours prior to starting.
2. Parking Brake & Gear Selection: Engage the parking brake. Put the vehicle in Park (automatic transmission) or Neutral (manual transmission).
3. Turn Off Accessories: Switch off all accessories, including HVAC, lights, and any aftermarket electrical equipment.
4. Idle Warm-up: Start the engine and let it idle for at least 2 minutes, until the engine coolant temperature reaches 65°C (149°F).
5. Elevated Idle: Run the engine for 6.5 minutes under these conditions:
   • MAF parameter between 4-30 g/s
   • Engine speed steady between 1000-3000 RPM
6. Idle Again: Return the engine to idle for 1 minute.
7. Low Speed, Low Load: Apply and hold the brake pedal, shift to Drive (automatic) or depress the clutch (manual), and operate for 2 minutes under these conditions:
   • Accelerator pedal angle (TP Sensor) 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 idle periods.
8. Idle Return: Release the accelerator, shift to Park (automatic) or Neutral (manual), and idle for 2 minutes.
9. Throttle Bursts: Quickly depress the accelerator pedal until the TP Sensor Angle is more than 8 percent, then release to idle. Repeat this three times.
10. Idle Period: Allow the engine to idle for at least 2 minutes.
11. Slow Speed Drive: Release the parking brake and drive at 24 km/h (15 mph) or slower for 2 minutes.
12. Highway Speed Drive: Continue driving for at least 5.5 miles between 45-112 km/h (28-70 mph), reaching at least 80 km/h (50 mph).
13. Deceleration: Release the accelerator pedal for at least 2 seconds to allow for deceleration fuel cut-off.
14. Moderate Acceleration: Depress the accelerator pedal to increase the TP Sensor angle by 3-20 percent and maintain a safe speed for 1 minute.
15. Stop and Idle (Drive): Safely stop the vehicle, keeping it in Drive (automatic) or Neutral with clutch depressed (manual) and parking brake applied. Idle for 2 minutes.
16. Park and Idle: Shift to Park (automatic) and apply parking brake, or Neutral (manual) and release clutch.
17. Cool Down Period: Turn OFF the ignition and exit the vehicle. Do not disturb the vehicle for 45 minutes.
18. Monitor Check: After 45 minutes, check the Inspection/Maintenance (I/M) System Status with your OBD2 scanner. All monitors, including EVAP, should now display “YES” or “Ready”.

If the EVAP Monitor is Still “Not Ready”

• Patience is Key: If the EVAP monitor is still “Not Ready,” it might require repeating steps 12-18 up to six more times, with 17-hour ignition OFF periods between each attempt.
• Check for DTCs: Use your OBD2 scanner to check for any Diagnostic Trouble Codes (DTCs). A DTC related to the EVAP system will prevent the monitor from setting to “Ready.” Address any DTCs first.
• Professional Assistance: If you’ve followed the procedure multiple times and the monitor remains “Not Ready,” it’s advisable to seek assistance from a qualified mechanic. There might be an underlying issue within the EVAP system that requires professional diagnosis and repair.

Conclusion

Dealing with an “OBD2 EVAP Not Ready” status can be time-consuming, especially on GM vehicles. By understanding the process and diligently following the GM Inspection/Maintenance procedure outlined above, you can increase your chances of resetting the monitor and ensuring your vehicle is ready for emissions testing. Remember to be patient, and if issues persist, don’t hesitate to consult a professional.