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Before you call…

If you need assistance regarding CARB’s heavy-duty diesel vehicle regulations first try the following tools:

2010 engine replacement guide icon


If you need assistance please fill out the Diesel Hotline Assistance Form and staff will work to get back to you in one to three business days. Near compliance and reporting deadlines, replies may take longer. Emails will be answered in the order that they are received.


To receive help by phone contact us at 1-866-6DIESEL (1-866-634-3735). Staff are available to answer questions in English, Spanish or Punjabi.

Calls are answered between 8:00 a.m. and 5:00 p.m, Monday through Friday; you can leave a voicemail after business hours. Calls are answered in the order they are received. During high call volume periods, there may be longer wait times. Ideal times to call are from 8 AM to 9:30 AM and 1 PM to 2:30 PM. Wait and response times are longest near compliance and reporting deadlines, so contact us early!

Staff is not available to assist walk-in visitors at our facilities. Walk-in visitors will be turned away.