The Non-Negotiable Answer for California Drivers
If your Check Engine Light (CEL), also known as the Malfunction Indicator Lamp (MIL)—is illuminated on your dashboard, here is the short answer you need to know:
Yes. If your Check Engine Light is on, your vehicle will automatically fail its California Smog Check.
This rule is non-negotiable across all official STAR and non-STAR Smog Check stations, including ours here in Torrance. The illuminated light signals a potential fault in your vehicle’s emissions control system, and California law mandates that any vehicle with an active emissions fault cannot pass the inspection.
The Real Culprit: Understanding “Readiness Monitors”
While the Check Engine Light is the visible warning, the underlying issue that causes a smog failure is the status of your vehicle’s Readiness Monitors.
Every modern vehicle uses an On-Board Diagnostic (OBD) system to monitor emission components (like the catalytic converter, oxygen sensors, and fuel system). These monitors are a series of self-tests the car runs while you drive.
When a smog technician connects to your vehicle:
- If the CEL is ON: The system instantly reports an active fault, resulting in an automatic failure.
- If the CEL was recently OFF (or codes were cleared): The monitors will show as “Not Ready.”
What Does “Not Ready” Mean?
If you recently disconnected your battery or cleared a trouble code yourself, the Check Engine Light will turn off. However, the monitors will reset to “Not Ready.” Because they haven’t had enough driving time to complete their self-tests, the smog machine sees this as tampering or avoiding a known problem.
In California, a vehicle will fail the smog check if too many of its readiness monitors are “Not Ready.”
- For model years 1999 and older: Your car is allowed to have up to two monitors “Not Ready.”
- For model years 2000 and newer: Your car is allowed to have only one monitor “Not Ready” (or zero).
Action Plan: 3 Steps to Pass Smog with a Check Engine Light
If you live in the Torrance area and your smog inspection is due, do not come in with a Check Engine Light on. Instead, follow these three steps:
Step 1: Get the Diagnostic Code Read
The Check Engine Light is just a warning. You need to know the specific diagnostic trouble code (DTC) to understand the repair needed.
- Most auto parts stores offer free diagnostic code reading.
- The code will look like P0420 (Catalyst System Efficiency Below Threshold) or P0300 (Random/Multiple Cylinder Misfire Detected).
Step 2: Repair the Underlying Issue
Once you have the code, you must repair the component causing the error. This is often the most expensive and time-consuming part, but it’s necessary for passing smog and maintaining your car’s efficiency. Common repairs include:
- Replacing a faulty oxygen sensor.
- Tightening a loose gas cap (yes, this causes a CEL!).
- Repairing a vacuum leak.
Step 3: Complete a “Drive Cycle” to Set the Monitors
After the repair, the trouble codes will be cleared, and your monitors will be reset to “Not Ready.” You must now perform a Drive Cycle to allow the monitors to run their self-tests and set back to “Ready.”
A proper drive cycle involves a mix of city and highway driving over several days. While every manufacturer has a unique cycle, a general approach is:
- Start with a cold engine.
- Drive at a steady speed (e.g., 30–55 mph) for at least 10 minutes.
- Include some stop-and-go driving.
- Avoid driving aggressively.
You can purchase a cheap OBD-II scanner to verify your monitors are “Ready” before you come in for your test.
Smog Check Due? Trust EZ Smog Torrance, a Certified STAR Station
Dealing with a Check Engine Light can be stressful, but knowing the California rules saves you time, money, and a retest fee.
As a certified STAR Station in Torrance, we are qualified to perform all smog checks, including those for vehicles requiring extra scrutiny. We get you in and out fast, but we can only pass vehicles that meet the strict standards.
Don’t risk a failure! Address your Check Engine Light first. Once your light is off and your readiness monitors are set, visit us for a fast, hassle-free smog inspection.
Ready to get certified? Get in touch.
