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Clean Truck Check On-Board Diagnostic Testing Recommended Practices

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OBD Testing Recommended Practices

  • If your Malfunction Indicator Light is on, get your vehicle repaired as soon as possible.
  • Don’t wait. Do the OBD test early in the compliance window so there will be time to fix any issues and re-test your vehicle, if necessary, by the compliance deadline.
  • Avoid clearing codes. OBD systems can require substantial vehicle operation to be able to complete diagnostic tests. A vehicle that has not been operated enough will be considered “Not Ready” and will not pass the compliance test. Code clearing can occur when:
    • Disconnecting the battery.
    • Using an improperly installed battery disconnect (sometimes referred to as a “kill”) switch that disconnects power to the OBD system (it is OK if the switch just cuts power to accessories/lights/etc.)
    • Using an OBD scan tool to clear codes.
  • If your vehicle receives a “Not Ready” result, you should continue operating the vehicle under normal business practices for a few days and then have the vehicle retested.
  • Update to the most recent version of the OBD test device software available from your device vendor.
  • If you have a problem during testing, try:
    • Turning the vehicle ignition off and back on and testing again.
    • Ensuring all other devices connected to the vehicle (e.g., electronic activity logger, telematics device other than a CTC telematics device, dash camera, etc.) are removed before scanning. They can be reconnected after the CTC OBD scan.
  • Please ensure the test results appear in your CTC-VIS account when getting your vehicle(s) tested. If the test results do not show up within five minutes after completing the test, you may need to:
    • Re-test your vehicle.
    • Verify the communication between the vehicle and the OBD test device.
    • Ensure the internet connection is stable.
    • Ensuring all other devices connected to the vehicle (e.g., electronic activity logger, telematics device other than a CTC telematics device, dash camera, etc.) are removed before scanning. They can be reconnected after the CTC OBD scan.
  • If the results still do not appear after multiple attempts during your emissions compliance testing, please email us at hdim@arb.ca.gov.