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There are also two exemption rules for gas powered vehicles; the 4-year rule for transfer applications and a 6-year rule for renewal applications. Under these rules the gas powered vehicles are exempt from smog under their respective time frames. Neither of these rules apply to diesel vehicles.
Testing is very simple and consists of three tests. An OBDII test, a visual inspection, and a smoke test.
OBD II Test
In the OBDII test the technician will take a scanner and check for any "silent" codes. These are codes that do not make the check engine light illuminate. A check engine light will cause an automatic failure, so have that fixed before going to get testes. Note that simply turning off the light by clearing the code may not work because the code may still be stored in the PCM.
The visual inspection is very simple too. The technician will look over the vehicle for any obvious non-approved modifications. This is where you are most likely to get hung up. Come prepared to fight this part if you have too.
There are many modifications you can do to your vehicle. Some are exempt by default, and some have been exempted by an Executive Order (EO). Many aftermarket companies spend lots of money to make their products meet CARB requirements and apply for an EO number. This EO number proves that your modification has been approved by CARB.
The most common failure is an aftermarket air intake without a CARB EO number. Quite frankly, that's hog wash. CARB has made it abundantly clear that ALL aftermarket air cleaners and intakes are exempt, and do not require a CARB EO number. Some intakes do have EO numbers assigned. Why? I have no clue. There is no real need for them since they are all exempt anyway.
The second most common failure is for an after market exhaust. The same thing goes for exhaust as for intakes, all after market exhausts are exempt. There is one exception, and that is if your truck originally had a catalyst system such as a catalytic converter or DPF system. Removal of either of these systems are grounds for immediate failure. Other than that, all exhaust systems are exempt.
There are just a few other things to note about the visual inspection. The technicians do not go home and study up on aftermarket part identification. They also do not spend too much time looking. The guidelines set forth to the technicians state to look for obvious violations. I will allow you to make your own deductions and conclusions with this information.
Smog technicians have been advised to pay special attention to vehicles that sport performance shop stickers. If you have a rear window full of stickers from your favorite diesel performance company, expect some extra scrutiny from the technician.
This is a silly test to fail. If you have modifications to your vehicle such as a tuner, set the tuner to stock and you should have no problem passing this test. The technician is going to observe the crank case and tailpipe for smoke.
The technician is looking for blue, white, or grey smoke. There are some clearly defined fail criteria here; 1) Any visible smoke while at idle, 2) Any visible smoke from the crank case, and 3) a smoke plume observed 5-15 feet from the tail pipe(s) that lingers for more than 3 seconds.
Smoke from any area other than the crank case or tail pipe does not constitute a failure.
"What about extra fuel tanks?" Answer: Extra fuel tanks without evaporation controls are not cause for a smog check failure.
"What about alternative fuels?" Answer: There are currently no plans to have fuel samples tested as part of the smog test.
"Can I run a straight-pipe muffler or muffler delete?" Answer: Yes and no. Mufflers are not an emissions related device and therefor have no bearing on you passing or failing your emissions test. So for the sake of this article, yes you can delete your muffler. However, according to California law all vehicles must be equipped with a muffler. So you will pass your smog check, but you might get a ticket down the road. (VC 27150)
"What other parts do not need a CARB EO number?" Answer: Air Cleaners, "Air Horn" intakes, auxiliary fuel tanks, fuel pumps, added fuel filters, exhaust brakes, and any exhaust modification after the emission control component are all CARB exempt.
"Can I download a quick-reference guide of what does and does not need a CARB EO number?" Answer: Yes. Make sure to take a copy to your smog station in case you run into resistance. SMOG Quick Reference Guide
The regulation applies to nearly all privately and federally owned diesel fueled trucks and buses and to privately and publicly owned school buses with a gross vehicle weight rating (GVWR) greater than 14,000 pounds.
Certain parts of El Dorado, Placer, Riverside, San Bernardino, San Diego, and Sonoma counties are exempt from testing. If you live in one of those counties, enter your zip code here to find out which "program area" you are in, as you could be exempt:
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