DPF deletes, smoke and Clean Truck Check

Short answer: no, a DPF-deleted, EGR-deleted or emissions-tampered truck will not pass Clean Truck Check. Deleted or tampered systems fail, and they are illegal. Diesel Dynamix does not remove, bypass or help hide emissions equipment. A truck with its emissions systems intact and working is the only way to pass.

Deleted and tampered trucks fail. Full stop.

This needs to be said plainly because there is a lot of bad advice out there. Removing or disabling a diesel particulate filter (DPF), EGR valve, SCR system or other emissions equipment is illegal. Tuning an engine computer to hide that equipment is tampering too.

Tampered or deleted equipment is one of the common reasons trucks fail:

• On the OBD test (2013 and newer diesel, 2018 and newer alternative fuel), the tester reads the engine computer. A deleted or tuned truck will not report the way a working, unmodified system does.
• On the smoke opacity test (2012 and older diesel without OBD), the visual inspection checks emissions-control parts. Missing, disconnected or tampered parts fail the truck even if the smoke reading looks fine.

Beyond failing the test, non-compliant and tampered trucks face CARB citations and penalties, and California-registered vehicles can face a DMV registration hold. CARB sets the penalty amounts, so check CARB for current figures. For the reasons behind the rules, see why California enforces Clean Truck Check.

Our policy: we test and explain. We do not remove, bypass, tune out or otherwise defeat emissions equipment, and we do not help anyone pass with a deleted truck.

Can a reinstalled DPF pass Clean Truck Check?

A truck that has had its emissions equipment properly restored, and whose systems are working, can be tested like any other truck. It still has to pass on its own. Work with a qualified diesel emissions repair shop to restore the correct parts and software, then drive the truck normally so readiness monitors can set before you test. See our post on readiness monitors and the check engine light.

DPF faults and the OBD test

You do not need a delete for the DPF to cause trouble. A DPF fault code or warning on an OBD-equipped truck is an emissions fault, and an emissions fault with the check engine light on is a common reason for failure.

If your dash shows a DPF warning or the truck is overdue for a regeneration, deal with it before the test:

• Follow the engine maker's procedure for regeneration.
• If regeneration does not clear the warning, have a repair shop check the DPF and its sensors.
• Ask your shop whether DPF cleaning is due.

Do not clear codes right before the test. That resets readiness monitors and can cause a failure on its own.

What causes excess smoke on the opacity test

For older non-OBD diesels, the smoke opacity test measures how much smoke the exhaust gives off. Common causes of excessive smoke:

• Worn or leaking injectors
• A dirty air filter or restricted intake
• Turbo problems
• Exhaust leaks
• A cracked or plugged DPF
• A cold engine. Smoke goes up when the engine is not at operating temperature.

Black smoke vs blue smoke

Black smoke from a diesel usually points to fuel and air problems, such as injectors, a restricted intake or turbo trouble. Blue smoke usually points to oil being burned. Either one can fail the opacity test. A repair shop can tell you which you have and why.

How to reduce smoke opacity before the test

1. Fix known problems first. Injectors, air filter, turbo and exhaust leaks.
2. Check the DPF, if the truck has one. It must be installed, intact and not overdue for cleaning.
3. Confirm emissions parts are present and connected, since the visual inspection checks them.
4. Warm the engine fully before the test.
5. Book the test once the repairs are done.

Our guide on how to pass the CARB smoke test goes deeper on diesel smoke test preparation.

What the visual inspection looks at

On older diesels that take the smoke opacity test, the visual inspection is where tampering usually shows up. The tester looks at the emissions-control parts that belong on that engine and checks that they are present, connected and not tampered with. A part that is missing, unplugged or modified fails the truck, no matter how clean the smoke reading is.

That is why "it doesn't smoke" is not the same as "it will pass." A deleted truck can blow a low reading and still fail.

Do aftermarket tunes cause problems?

Any tune that disables or hides emissions equipment is tampering, and it fails. If you are unsure whether software on your truck has been changed, ask a qualified repair shop to check it before you book a test.

If you just bought a truck with a delete

It happens, especially with used trucks. The path forward is the same: have a qualified shop restore the emissions equipment, make sure it works, and then test. Until then, the truck cannot pass Clean Truck Check. If you are unsure what was changed, ask a repair shop to inspect it before you book.

How Diesel Dynamix helps

We test working, legal trucks on site across Southern California, at your yard, jobsite, terminal, port or home. We run the CARB-verified OBD test or the smoke opacity test plus visual inspection, explain the result in plain English and retest after your shop finishes repairs. We do not do repairs and we do not help with deletes.

• Smoke opacity testing
• CARB OBD testing
• What to do after a failed test

Book a test, or call, text or WhatsApp (858) 342-8328.