---
title: "Nathan Simpson — Clean Truck Check, Modesto, CA | CTC Finder"
description: "Nathan Simpson in Modesto, CA is on CARB's Clean Truck Check tester list. Offers mobile testing, OBD testing, smoke opacity (non-OBD) testing. Phone, address…"
url: "https://ctcfinder.com/tester/nathan-simpson-modesto/"
updated: "2026-11-01"
publisher: "CTC Finder (independent directory, not affiliated with CARB)"
---

# Nathan Simpson

Clean Truck Check tester in Modesto, CA (Stanislaus County).

> CTC Finder is an independent directory, not affiliated with CARB. Tester data: CARB Clean Truck Check public tester list, last checked November 1, 2026. Confirm services, hours and prices with the tester.

| Field | Value |
|---|---|
| Location | Modesto, CA 95354 |
| County | Stanislaus County |
| Phone | (209) 678-8549 |
| Mobile testing | Yes |
| OBD testing | Yes |
| Smoke opacity (non-OBD) | Yes |
| Motorhomes | No |
| Credentialed testers | 1 |
| Last verified | 2026-11-01 |

## Which trucks Nathan Simpson can test

| Your vehicle | Test required | This tester |
|---|---|---|
| Diesel, model year 2013 or newer | OBD scan | Yes |
| Alternative fuel (natural gas, propane), 2018 or newer | OBD scan | Yes |
| Diesel, model year 2012 or older (no OBD) | Smoke opacity test (SAE J1667) plus visual inspection | Yes |
| California-registered motorhome | Same test as above by engine year, once a year | Not listed |

## Clean Truck Check testers in Stanislaus County

Nathan Simpson is one of 53 testing businesses in Stanislaus County on CARB's public tester list. 47 of them offer mobile testing and 22 do smoke opacity tests. In Modesto itself there are 23 listed businesses, 21 of them mobile.

## When your truck is due

Most trucks test twice a year, on a schedule tied to the DMV registration expiration date. CARB says OBD trucks move to four tests a year beginning October 2027. California-registered (non-commercial) motorhomes and agricultural vehicles test once a year. See the [deadline guide](https://ctcfinder.com/guide/deadlines-2026-2027/). You can test up to 90 days before a deadline. Free email reminders: https://ctcfinder.com/reminders/

## Frequently asked questions

### Does Nathan Simpson offer mobile Clean Truck Check testing?

Yes. Nathan Simpson says on CARB's tester list that it offers mobile testing, so it can come to your yard or job site. Ask about a trip fee when you call.

### Can Nathan Simpson test a 2012 or older diesel truck?

Yes. Nathan Simpson lists smoke opacity testing, the test CARB requires for diesel trucks of model year 2012 and older (no OBD). See [OBD vs smoke opacity](https://ctcfinder.com/guide/obd-vs-smoke-opacity-test/).

### How much does Nathan Simpson charge for a Clean Truck Check?

Nathan Simpson has not published prices with us; call (209) 678-8549 for a quote. Published California prices are usually $50–$135 per vehicle for an OBD test and $190–$200 for a smoke opacity test, plus CARB's annual fee ($32.13 in 2026). See the [cost guide](https://ctcfinder.com/guide/cost/).

### Is Nathan Simpson a CARB-credentialed tester?

Nathan Simpson appears on CARB's public Clean Truck Check tester list, last checked November 1, 2026. Only credentialed testers can submit results to CARB; after the test, confirm the passing result shows for your vehicle in CTC-VIS.

## Other testers nearby

- **[S S DPF Filter Cleaning](https://ctcfinder.com/tester/s-s-dpf-filter-cleaning-modesto/)** — 220 Beard Ave, Modesto, CA 95354 — (209) 649-4581 — 1 mi. Services: mobile testing, OBD testing, smoke opacity (non-OBD) testing, motorhome testing.
- **[S&S dpf filter cleaning](https://ctcfinder.com/tester/s-and-s-dpf-filter-cleaning-modesto/)** — 220 Beard Ave, Modesto, CA 95354 — (209) 622-6134 — 1 mi. Services: mobile testing, OBD testing, smoke opacity (non-OBD) testing, motorhome testing.
- **[Walkers Automotive](https://ctcfinder.com/tester/walkers-automotive-modesto/)** — 407 14th St, Modesto, CA 95354 — (209) 527-5577 — 1 mi. Services: mobile testing, OBD testing, motorhome testing.
- **[A&B Truck Repair, Inc.](https://ctcfinder.com/tester/a-and-b-truck-repair-inc-modesto-2/)** — 959 S 9th St, Modesto, CA 95351 — (209) 527-6971 — 2 mi. Services: mobile testing, OBD testing, smoke opacity (non-OBD) testing, motorhome testing.
- **[J And L Complete Automotive Repair Inc.](https://ctcfinder.com/tester/j-and-l-complete-automotive-repair-inc-modesto/)** — 711 Kansas Avenue Ext, Modesto, CA 95351 — (209) 480-0010 — 2 mi. Services: mobile testing, OBD testing, smoke opacity (non-OBD) testing, motorhome testing.
- **[Linarez Transportatoin LLC](https://ctcfinder.com/tester/linarez-transportatoin-llc-modesto/)** — 1632 Woodworth Ave, Modesto, CA 95351 — (209) 416-9298 — 2 mi. Services: OBD testing.