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Test Preparation

How to walk into your CTC test prepared

Most first-try failures come down to readiness, paperwork, or active fault codes — all of which you can fix before your appointment.

Before you book the appointment

  • Confirm the testing service supports your engine: OBD for most 2013+ heavy-duty diesels, smoke opacity for older or non-OBD-eligible vehicles.
  • Decide whether a mobile Certified Tester at your yard makes more sense than driving to a shop.
  • Have your VIN, registration, and CARB account info ready.

The night before

  • Top off DEF and coolant. Low coolant can trigger a fault and fail your test.
  • Check the dash — resolve any active check engine, DEF, or SCR warnings.
  • If monitors aren’t set, plan a drive cycle in the morning.

The day of the test

  • Arrive with the engine warm and at operating temperature.
  • Don’t clear DTCs or disconnect the battery beforehand — that resets monitors.
  • If a regen is active when you pull in, let it finish.
  • If you have done recent repairs or cleared codes, complete at least 5 full drive cycles to ensure all readiness monitors are set before showing up.

If you fail

Ask the Certified Tester for the specific failure reason and any DTCs captured. Common causes are: incomplete monitors, active DTCs (especially aftertreatment), failed NOx efficiency, or a leaking exhaust system on smoke opacity tests. Repair, complete a drive cycle, and re-test.

Not a substitute for CARB guidance. CTC Connect publishes plain-English explanations of publicly available compliance information. Always verify rules with the official CARB Clean Truck Check program. Need a Certified Tester? Search the directory.