California's Truck Idling Rule: The 5-Minute Limit, the Exceptions, and Regens

The direct answer: in California, a diesel commercial vehicle over 10,000 lbs GVWR may not idle for more than 5 consecutive minutes at any location. The rule is the state’s idling control measure, Title 13, California Code of Regulations, section 2485. It applies to California-based and out-of-state trucks alike. There are specific exceptions — including idling that is needed for servicing, diagnosis or an emissions regeneration in progress.

Who the rule covers

Section 2485(b) applies to anyone who owns, operates or causes to operate a diesel-fueled commercial motor vehicle with a gross vehicle weight rating over 10,000 pounds that is, or must be, licensed for highway use — California-based and non-California-based vehicles both. It also covers idle-reduction equipment installed on those trucks: auxiliary power systems (APS), fuel-fired heaters and similar devices.

The limits

• Primary engine: no idling for more than 5 consecutive minutes at any location (section 2485(c)(1)(B)1).
• Diesel APS: no running a diesel-fueled APS for more than 5 minutes when within 100 feet of a restricted area (section 2485(c)(1)(B)2).
• Restricted area means property zoned for houses or apartments, schools, hotels, motels, hospitals, senior care or child care facilities, with one or more of those on it (section 2485(h)).

The Clean Idle label exception

A truck whose engine is certified to California’s optional low-NOx idling standard and carries the matching label — commonly called the Clean Idle label — is not held to the 5-minute primary-engine limit, except within 100 feet of a restricted area (section 2485(d)(1)). Near homes, schools, hotels and the rest, the 5-minute limit still applies.

Exceptions that matter in day-to-day work

Section 2485(d)(2) lists the situations where the idling limit does not apply. The ones drivers and shops meet most often:

• Stopped in traffic, at a signal or control device, or at the direction of a peace officer
• Queuing, as long as the truck stays more than 100 feet from any restricted area the whole time
• Forced to stay put by adverse weather affecting safe operation, or by mechanical difficulties outside the driver’s control
• Idling needed to verify the truck is safe, as part of a daily inspection or otherwise, where idling is mandatory for that check
• Idling that is mandatory for testing, servicing, repair or diagnosis — including regeneration of the exhaust emission control device while the dash indicator shows a regen in progress
• Powering a PTO for work the truck is built for — cargo temperature, a lift, crane, pump, mixer or similar equipment
• Running heat, A/C or defrost solely to prevent a safety or health emergency

The sleeper-berth exception that once allowed main-engine idling for heat or air conditioning ended on January 1, 2008. Local ordinances can be stricter, and the rule does not permit idling that other law prohibits (section 2485(e)).

Auxiliary power units and fuel-fired heaters

On trucks with 2007 or newer engines, a diesel APS may only be run in California if it meets the rule’s particulate requirements — a verified Level 3 particulate control, exhaust routed into the truck’s exhaust upstream of the particulate filter, or certification to the stricter standard — and carries the required label. Fuel-fired heaters on those trucks must meet California’s emission standards (section 2485(c)(2)(D) and (c)(3)). If you are adding or replacing an APS, confirm its compliance before it goes on the truck.

Paperwork the driver must be able to show

On request, the driver must give enforcement personnel a driver’s license, the vehicle registration, and the motor carrier’s information. The carrier that dispatches the truck must supply that information to the driver: business name, street address with state and ZIP, and a contact person’s name and business phone (section 2485(c)(1)(C)–(D)).

Who enforces it

The Air Resources Board, peace officers, and local air pollution control and air quality management districts (section 2485(f)). Penalties are set by the Health and Safety Code sections the regulation lists.

Why long idling is hard on a modern diesel anyway

Beyond the rule, extended idle is a poor duty cycle for an engine with a particulate filter. Exhaust at idle runs cool, so soot that would burn off on the highway builds up instead, and the truck asks for regenerations more often. Trucks that idle for long periods also tend to show it in fuel economy. If a truck keeps asking for regens or a regen won’t complete, that is a diagnosis, not a habit to work around — see DPF cleaning and forced regen service.

Common questions

Does the 5-minute idling limit apply to out-of-state trucks?

Yes. Section 2485(b) covers both California-based and non-California-based diesel commercial vehicles over 10,000 lbs GVWR operating in the state.

Can I idle during a parked regen?

The rule exempts idling that is mandatory for servicing or for regeneration of the emission control device while the dash indicator shows a regen in progress (section 2485(d)(2)(G)). Once the regen is done, the 5-minute limit applies again.

Does a Clean Idle label let me idle anywhere?

No. The label lifts the 5-minute primary-engine limit except within 100 feet of a restricted area — homes, schools, hotels, motels, hospitals, senior care and child care facilities.

Can I idle for heat or A/C in the sleeper?

Not on the main engine beyond 5 minutes, except to prevent a safety or health emergency. A compliant APS or other idle-reduction equipment is the usual answer, within the 100-foot rule for diesel APS units.

Summarized from Title 13, California Code of Regulations, section 2485 (text via Cornell LII), reviewed 2026-10-20. This is a plain-language summary, not legal advice; the regulation and the enforcing agency govern.