Most smog failures are avoidable. Fix any warning light first, warm the engine, keep the oil fresh, tighten the gas cap and make sure the emissions monitors are ready. A short checklist before you drive over saves a failed test.
Key takeaways
- Resolve warning lights before testing.
- Warm the engine for ten minutes.
- Allow monitors to reset after battery work.
Deal with the check engine light
A lit check engine light fails the test. Have it diagnosed and repaired first. Do not just clear the code, because clearing resets the monitors and the light can return.
Warm the engine
A warm engine and catalytic converter run cleaner. Drive for about ten minutes at steady speed before arriving.
Oil and basic maintenance
Fresh oil reduces hydrocarbons from contaminated oil. If your oil change is overdue, do it before the test. A clogged air filter and worn plugs can hurt results too.
Gas cap and evap system
A cap that does not seal can trigger the evaporative system check. Tighten it until it clicks, and replace it if the seal is cracked.
Make sure monitors are ready
After a battery replacement or code reset, the computer needs time and a mix of driving to complete its readiness monitors. Several days of normal driving usually works. Ask us if you are unsure.
Tire pressure and other basics
If your car needs a dynamometer test, tires must be in good condition. Keep tires at the correct pressure and avoid driving with a heavy load.
What technicians see most often
The most common avoidable problems are a lit warning light, a loose gas cap, a car that was driven only a short distance before the test and monitors that are not ready after a battery change. Another common issue is old oil that has not been changed in a long time. None of these costs much to fix beforehand, but each can turn a quick test into a failed one and a second trip.
What not to do before the test
Do not clear codes right before testing, because that resets the monitors. Do not use fuel additives in the hope of a miracle, because they rarely help and can mask a problem. Do not arrive on fumes or with a nearly empty tank, since the technician needs some fuel for the test. Do not skip a needed repair in the hope the car will squeak through, because failing costs more in time than fixing it first.
Need help in south Bakersfield?
Questions about smog check? Read our Smog Check page, call (661) 599-9098 or request a time. Peña's Auto Electric, Smog & Repair, 303 Taft Hwy, Suite B, Bakersfield, CA 93307. Mon to Fri 9:30 AM to 5:30 PM, Sat 8 AM to 1 PM.
Frequently asked questions
Should I clear codes before testing?
No. It resets monitors and can cause a not-ready result.
Does warming up help?
Yes. A warm engine and converter run cleaner.
Should I change oil first?
If it is overdue, yes.
What if monitors are not ready?
Drive normally for several days and return.
Related reading
Sources
- California Bureau of Automotive Repair, Smog Check program and consumer information