Clean Truck Check Credentialed Tester

CARB Clean Truck Check 2027 Testing Changes — What Fleets Need to Know

Last updated: · See changelog

California's Clean Truck Check program shifts from biannual to quarterly compliance testing for diesel and alternative-fuel vehicles over 14,000 lb GVWR. The rule is written against compliance deadlines falling in 2028 and later — but because every Clean Truck Check deadline has a 90-day window that opens beforethe deadline date, fleets with Q1 2028 deadlines start executing under quarterly rules in October 2027. That timing is the most important thing to take away from this page, and it is the thing most fleet operators we've talked with did not know.

Why "2028" sounds farther away than it is

CARB's rule applies the quarterly cadence to compliance deadlines on or after January 1, 2028. That phrasing is technically correct and operationally misleading. Clean Truck Check compliance deadlines are not check-the-box dates you can wait until — they have a fixed 90-day testing window that opens 90 days before the deadline. A vehicle with a January 15, 2028 deadline must have a passing test on file sometime between approximately October 17, 2027 and January 15, 2028. CARB blocks early submission outside the 90-day window, and late submission triggers a non-compliance flag.

What this means in practice: any fleet vehicle with a Q1 2028 compliance deadline (January, February, or March of 2028) starts its first-ever quarterly-cadence testing window during Q4 2027. For most fleets, that is the back half of October 2027 onward. Fleets are going to start running into the new cadence during their 2027 budget year — not 2028.

We're writing this in mid-2026, which means anyone reading this has about 14-17 months before the quarterly cadence begins executing for early-2028 deadlines. That is enough time to switch testing approaches if it turns out to be the right call. It is not enough time to wait until the change is "close" and still have flexibility.

What is changing, in detail

The current Clean Truck Check program requires a passing compliance test twice per year against an assigned deadline. Vehicle owners pay an annual compliance fee through CTC-VIS, schedule (or run, if subscribing to Clean Truck Check device) two tests against their two annual deadlines, and download the compliance certificate once both tests are on file. Vehicles found non-compliant face DMV registration holds and roadside enforcement.

Starting with deadlines in 2028 and after, the cadence becomes quarterly — four passing tests per year per vehicle. The mechanics of testing, the assigned deadline system, the 90-day pre-deadline window, the annual fee structure, and the consequence model all stay the same. The only thing that changes is frequency: twice becomes four times.

For a fleet that today schedules CTC testing alongside other preventative maintenance, that means coordinating four testing events per truck per year instead of two. For a fleet that uses mobile testing services (e.g. Clean Truck Check Pro in Southern California), it means scheduling four mobile visits per truck per year. For a fleet on an Clean Truck Check device subscription model (e.g. Smart CTC), the device handles all four windows automatically — the only change visible to the operator is whatever happens in CTC-VIS.

Who is affected

Clean Truck Check covers most non-gasoline vehicles over 14,000 pounds GVWR operating in California. The 2027 cadence change applies to all of them; the rule does not carve out specific vehicle classes from the new frequency.

  • Diesel heavy-duty vehicles — the bulk of the program. On-highway tractors, vocational trucks, dump trucks, concrete mixers, and similar over 14,000 lb GVWR.
  • Heavy-duty alternative-fuel vehicles — CNG, LNG, propane, and certain hybrid configurations are included.
  • California-registered motorhomes over 14,000 lb GVWR — included under the motorhome subprogram with its own test workflow.
  • Out-of-state and out-of-country carriers operating in California— same rule. CARB's jurisdiction attaches to operation in California, not registration state.

The smallest fleets — single-truck owner-operators, one-truck family businesses — see the highest relative impact because there is no batching efficiency. Each visit is a full shop-visit overhead spread across one truck. Large fleets see higher absolute cost (more trucks × more tests) but the per-truck efficiency stays roughly constant.

The Real Cost of Downtime

Test-fee math is the obvious cost. Downtime is the second cost and often the bigger one for fleets running their trucks hard. In-shop testing typically pulls a truck from revenue service for 1-3 hours including drive-time, shop wait, and the test itself. At a conservative $80/hour revenue-loss figure, that's $80-$240 of foregone revenue per test, on top of the test fee.

For a 5-truck fleet running in-shop testing today, that's roughly 10 truck-hours per year of testing downtime — 20 truck-hours in 2028. For a 20-truck fleet on mixed in-shop/mobile, today's 40 truck-hours becomes 80. Mobile on-site testing cuts downtime per test substantially (typically 20-40 minutes per truck). Clean Truck Check device testing reduces it to zero — the test runs during normal operation.

When you include downtime, the 2x-cost ratio between today and 2028 holds for in-shop and mobile, but disappears for Clean Truck Check device — and the Clean Truck Check device line item that was "more expensive than in-shop today" on a per-truck basis often becomes the cheapest option once 2028 cadence + downtime are accounted for. That is the wedge.

Preparation strategies

Five things to consider through 2026 and into 2027 if you operate trucks subject to Clean Truck Check:

  1. Audit your current testing approach. Pull your last 12 months of CTC test invoices and total them. That number doubles in 2028 if you change nothing else. Operators who run this calculation typically discover the line item is larger than they remembered.
  2. Map your testing windows for Q1 and Q2 2028. Your CTC-VIS dashboard shows each vehicle's next deadline. For any deadline falling in the first half of 2028, that's your first quarterly-cadence window — start scheduling against it as if it were today.
  3. Lock subscription pricing while market awareness is low. Subscription pricing across Clean Truck Check device providers tends to rise as demand visibility increases. Subscriptions signed today typically lock multi-year rates; subscriptions signed in late 2027 will be quoted against tighter capacity. (Disclosure: this site is operated by the team behind Smart CTC, which sells one of these subscriptions. See the comparison page for the honest case for and against Clean Truck Check device.)
  4. Renegotiate with your shop if you continue in-shop testing.Shops that handle CTC volume will get more valuable as 2028 approaches. If you're a regular customer, now is the time to lock in a per-test rate and reserve recurring slots. Shops will be unenthusiastic about doing this once their calendar fills up.
  5. Document compliance proactively. Whatever path you choose, keep certificates organized by vehicle and quarter. Quarterly cadence quadruples the document-management surface area, which is annoying enough that operators have, in our experience, started using it as a reason to switch to Clean Truck Check device (which handles the recordkeeping automatically).

Common questions

Is the 2027 change definite, or could it be delayed?
The shift to quarterly compliance testing is in adopted CARB regulation, not a proposed rule. It is scheduled to apply to compliance deadlines in 2028 onward. CARB has, historically, granted limited enforcement discretion on early-phase Clean Truck Check requirements — but the rule itself is on the books and fleets should plan as if it will apply. Confirm against the current CARB Clean Truck Check page before relying on any specific date for an audit response.
Does this affect out-of-state trucks operating in California?
Yes. Clean Truck Check applies to any non-gasoline vehicle over 14,000 lb GVWR operating in California, regardless of where the vehicle is registered or the carrier is based. Out-of-state carriers crossing into California are subject to the same testing frequency as California-based fleets.
Will fees increase along with frequency?
The annual compliance fee per vehicle is set by CARB rule and is paid through CTC-VIS. The per-vehicle annual fee is not directly tied to test count. However, per-test costs paid to third-party testers (in-shop or mobile) scale with frequency by definition — four tests per year cost more than two. Clean Truck Check device subscription pricing is structured to be flat regardless of test count.
How does CARB enforce the new frequency?
Enforcement is the same mechanism as today's biannual cadence: a vehicle without a current compliance certificate on file in CTC-VIS by its deadline is flagged non-compliant. Non-compliant vehicles face DMV registration holds and roadside enforcement risk. The quarterly cadence means a non-compliant vehicle is flagged four times per year instead of two — which raises the practical odds of getting caught.
What happens if my fleet has vehicles with deadlines spread across the year?
Each vehicle is tested against its own deadline. A 20-truck fleet with deadlines spread evenly across the calendar will be testing roughly five trucks per quarter starting in 2028. Most fleets don't naturally have evenly-spread deadlines, which means clusters of testing activity around the same week each quarter — a real scheduling problem for in-shop and mobile testing options that subscription Clean Truck Check device avoids.
When does the new cadence actually start affecting my fleet?
The first Q1 2028 compliance deadline opens its 90-day testing window in early October 2027. A truck with a January 15, 2028 deadline needs a passing test on file between approximately October 17, 2027 and January 15, 2028. So while CARB describes the change as 'effective for 2028 deadlines,' fleets with early-2028 deadlines start executing quarterly rules in Q4 2027.

Changelog

  • May 17, 2026 — initial publication.

Do the math for your fleet.

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What to do next

If you're weighing how to handle quarterly testing across your fleet, the side-by-side comparison is the fastest way to pressure-test your options.

Compare testing options →Lock subscription pricing (Smart CTC)

This page is published by the team behind CTC Directory, Smart CTC (Clean Truck Check device testing), and Clean Truck Check Pro (mobile testing). We have a commercial interest in two of the three options described above. We've made our best effort to present every option fairly. Always confirm specific regulatory details with CARB before relying on them for compliance decisions.