CTC Connection
Clean Truck Check Directory
Find a Certified Tester
Drive Cycle Guide

The heavy-duty diesel drive cycle, explained

If you walk into a Clean Truck Check OBD test with incomplete readiness monitors, you cannot pass. Here's how to complete a drive cycle so monitors are set before your appointment.

What is a drive cycle?

A drive cycle is a sequence of driving conditions designed to give the engine’s on-board diagnostics (OBD) system enough data to run its self-tests. When those tests finish, the corresponding readiness monitor flips from not ready to ready. A CARB CTC OBD submission requires the monitors that apply to your engine family to be in the “ready” state.

When you usually need to run one

  • After a recent battery disconnect or replacement.
  • After diagnostic codes (DTCs) were cleared at a shop.
  • After significant engine, sensor, or aftertreatment work.
  • If a previous Clean Truck Check submission failed with “monitors not ready.”

General heavy-duty diesel drive cycle

Exact requirements vary by manufacturer — always consult your engine OEM’s service literature first. A typical sequence looks like:

  1. Cold start. Begin with the engine fully cooled (typically an overnight soak).
  2. Idle warm-up. Idle 2–3 minutes after start.
  3. Steady highway cruise. Drive at a steady 50–65 mph for at least 20 continuous minutes.
  4. Vary load. Include several gentle accelerations and decelerations.
  5. Cool down. Allow a brief cool-down idle before shutting off.
  6. Re-scan. Verify readiness with a scan tool before driving to your Certified Tester.

Common reasons monitors stay “not ready”

  • Active or pending DTCs prevent monitors from completing.
  • Engine never reaches full operating temperature.
  • Drive cycle is interrupted by frequent stops or short trips.
  • Aftertreatment regenerations were not allowed to complete.

Before your appointment

Bring your VIN, registration, and any recent service records. If a regen cycle is actively running, let it finish before plugging into the Certified Tester's equipment. If you keep failing on monitor readiness, a diagnostic visit can find pending codes blocking the cycle.

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.