Accuracy Matters in CARB Testing, Especially When the Weather Doesn’t Cooperate

If you’ve lived in California long enough, you know how unpredictable our weather can be. One week we’re praying for rain. The next, we’re watching an atmospheric river roll in from San Francisco, stretch through the Valley, and reach as far north as Chico. This week is one of those moments, with steady rain expected for days on end.

At NorCal CARB Mobile, weather like this doesn’t change our priorities. It just means we have to be even more diligent.

We’re a fully mobile emissions testing company, serving customers from San Jose to Sacramento, and our job is simple in theory but demanding in practice: deliver accurate, compliant smoke opacity and OBD tests, no matter where we’re working.

Why Environment Matters in Smoke Opacity Testing

Smoke opacity testing is not just about plugging in a machine and hitting “go.” Instruments like the Wager 6500 and 6500+ are highly precise optical devices. They measure how much light is blocked by diesel exhaust particles during a snap-acceleration test.

That precision means environmental conditions matter.

Heavy rain, fog, mist, wind, and even high humidity can interfere with the optical path between the sensor and the exhaust plume. Rain droplets and airborne moisture can scatter light and introduce noise into the reading. That doesn’t mean the engine suddenly got dirtier. It means the environment can distort the measurement if the test isn’t handled correctly.

California regulations and SAE J1667 standards don’t prohibit testing in rain, but they do require valid, repeatable results. If the readings don’t meet strict consistency criteria, the test isn’t valid. Running more tests doesn’t fix that. Good judgment does.

How We Handle Challenging Conditions

Being mobile means we see it all. Clear Central Valley mornings, coastal humidity in the Bay Area, and now multi-day rain events driven by atmospheric rivers.

Our approach is straightforward:

• We verify calibration before testing, especially in wet or unstable weather.

• We make sure exhaust rain caps are fully open and that water isn’t crossing the optical path.

• We pay close attention to wind direction, shelter, and positioning to avoid plume disruption.

• If conditions are unstable and valid readings can’t be achieved, we pause or reschedule rather than force a questionable result.

We always err on the side of safety, accuracy, and compliance. That protects our customers and keeps their vehicles on the right side of CARB requirements.

Mobile Doesn’t Mean Cutting Corners

At NorCalCARBMobile.com, being mobile means bringing the same level of care and technical discipline to your location that you’d expect from a fixed testing site.

Whether we’re performing a smoke opacity test with a Wager 6500 or running standard OBD diagnostics, our goal is the same every time: accurate data, proper procedure, and clear communication.

California’s weather may swing from drought to downpour, but our standards don’t change. Rain or shine, from San Jose to Sacramento, we’re here to help our customers stay compliant and confident in their results.

If you ever have questions about testing conditions, timing, or what to expect during a weather event like this one, just ask. We believe informed customers are better protected customers.

And when the rain finally stops, we’ll still be rolling.