Can You Sell a Car with Check Engine Light on in California

You can legally sell a car with the check engine light on in California, but it’s not without risks and requirements. Sellers must disclose the issue, pass a smog check (if applicable), and avoid misrepresentation to stay compliant with state laws and protect themselves from liability.

Key Takeaways

• It’s legal to sell a car with the check engine light on in California—as long as you’re transparent about the issue and follow state disclosure rules.
• Smog checks are required for most used car sales, and a lit check engine light usually causes an automatic failure, making it harder to complete the sale.
• Full disclosure is mandatory—you must inform the buyer in writing about the check engine light and any known engine problems.
• Buyers may negotiate a lower price or walk away entirely if the light is on, especially if the issue isn’t explained or repaired.
• Repairing the issue before selling can increase your car’s value and make it easier to pass smog and close the deal quickly.
• Selling “as-is” doesn’t exempt you from disclosure—California law still requires honesty about known mechanical problems.
• Document everything—keep records of repairs, inspections, and conversations with buyers to protect yourself legally.

Can You Sell a Car with Check Engine Light on in California?

So, you’ve got a car that’s been reliable for years—until one day, the dreaded check engine light pops up on your dashboard. Now, you’re thinking about selling it, but you’re not sure if you even *can* sell it with that little orange warning staring back at you. The short answer? Yes, you can sell a car with the check engine light on in California. But it’s not as simple as just handing over the keys and walking away.

California has some of the strictest vehicle regulations in the U.S., especially when it comes to emissions and consumer protection. While the law doesn’t outright ban the sale of a car with a lit check engine light, it does impose important responsibilities on sellers. From disclosure requirements to smog check rules, there’s a lot to consider before listing your vehicle. Ignoring these rules could lead to fines, legal trouble, or a failed sale.

In this guide, we’ll walk you through everything you need to know about selling a car with the check engine light on in California—legally, ethically, and profitably. Whether you’re selling privately or trading in, understanding your obligations and options will help you make the best decision for your situation.

Understanding the Check Engine Light: What It Really Means

Before diving into the legalities of selling, it’s important to understand what that glowing icon actually means. The check engine light—also known as the malfunction indicator lamp (MIL)—is part of your car’s onboard diagnostics system (OBD-II). When it comes on, it’s signaling that the vehicle’s computer has detected a problem with the engine, transmission, or emissions system.

But not all check engine lights are created equal. Some issues are minor and inexpensive to fix—like a loose gas cap or a faulty oxygen sensor. Others can be serious, such as a failing catalytic converter, engine misfire, or problems with the fuel injection system. The severity of the issue can range from “drive it carefully” to “stop driving immediately.”

In California, the check engine light plays a particularly important role because of the state’s strict emissions standards. The OBD-II system is designed to monitor emissions-related components, and if it detects a fault, the light will illuminate. This directly affects your ability to pass a smog check—a requirement for most vehicle sales in the state.

Common Causes of the Check Engine Light

• Loose or damaged gas cap: One of the most common and easily fixable causes. A loose cap can allow fuel vapors to escape, triggering the light.
• Oxygen (O2) sensor failure: These sensors monitor exhaust gases and help regulate fuel mixture. A faulty sensor can reduce fuel efficiency and increase emissions.
• Catalytic converter issues: A failing converter can cause poor performance, reduced fuel economy, and high emissions. Repairs can be costly.
• Mass airflow (MAF) sensor problems: This sensor measures how much air enters the engine. If it’s dirty or malfunctioning, it can cause rough idling or stalling.
• Spark plug or ignition coil failure: These can cause engine misfires, leading to poor performance and increased emissions.
• Evaporative emissions (EVAP) system leaks: Small leaks in the fuel vapor system can trigger the light and fail a smog test.

Understanding the root cause of your check engine light is the first step in deciding whether to repair it before selling or disclose it to potential buyers. In many cases, a quick diagnostic scan at an auto parts store (often free) can tell you the trouble code and give you a clearer picture of what’s going on.

California Laws on Selling a Car with a Check Engine Light

Now that you know what the light means, let’s talk about the rules. California law doesn’t prohibit the sale of a vehicle simply because the check engine light is on. However, it does require sellers to be honest and transparent about the vehicle’s condition—especially when it comes to emissions and safety.

The key legal requirement is **disclosure**. Under California’s Vehicle Code and consumer protection laws, you must inform the buyer in writing if you know about any mechanical problems, including a lit check engine light. This is typically done using the **Vehicle Transfer and Release of Liability form** (REG 138) and a **smog certification**, if required.

Disclosure Requirements

California Civil Code § 1793.22 and the state’s lemon law provisions emphasize the importance of honesty in vehicle sales. While these laws primarily protect buyers of new cars, the principle of full disclosure extends to used car sales as well. Selling a car with a known issue—like a check engine light—without telling the buyer can be considered fraudulent misrepresentation.

This means you can’t just say, “I don’t know why the light is on” if you’ve had the car scanned or been told about a problem by a mechanic. If you’re aware of the issue, you must disclose it. Failure to do so could result in the buyer taking legal action, demanding a refund, or reporting you to the Department of Motor Vehicles (DMV).

Smog Check Requirements

One of the biggest hurdles when selling a car with the check engine light on is the **smog check**. In California, most vehicles being sold must pass a smog inspection within 90 days of the sale. This applies to cars that are more than four years old and are being transferred to a new owner.

Here’s the catch: **a lit check engine light will cause an automatic smog check failure**. The smog technician cannot complete the test if the MIL is on, regardless of whether the car actually emits excess pollutants. This is because the OBD-II system is designed to flag potential emissions problems, and the state takes these warnings seriously.

Even if the car runs fine and emissions are low, the light itself is enough to fail the test. This means that unless the light is off and all readiness monitors are set, the smog certificate cannot be issued.

Exceptions to Smog Check Rules

There are a few exceptions where a smog check isn’t required:

• Transfer between spouses, domestic partners, or parents and children
• Sale to a licensed dealer or dismantler
• Vehicles eight model years old or newer (as of 2024, this includes 2016 and newer models)
• Diesel vehicles from 1997 and older or with a gross vehicle weight rating (GVWR) over 14,000 lbs

If your sale falls under one of these categories, you may not need a smog check—even with the check engine light on. However, you’re still required to disclose the issue to the buyer.

Should You Repair the Check Engine Light Before Selling?

This is one of the most common questions from sellers: “Should I fix the problem before selling, or just disclose it and sell as-is?” The answer depends on several factors, including the cost of repair, the car’s overall condition, and how much you want to sell it for.

Pros of Repairing Before Selling

• Higher resale value: A car with a clean bill of health—including no check engine light—will typically sell for more than one with known issues.
• Easier to pass smog: Fixing the issue turns off the light and allows the car to pass the required smog check, making the sale smoother.
• More buyer confidence: Buyers are more likely to trust a seller who has addressed known problems. It shows responsibility and transparency.
• Faster sale: Cars without warning lights spend less time on the market. Buyers often avoid vehicles with check engine lights due to uncertainty.

Cons of Repairing Before Selling

• Upfront cost: Depending on the issue, repairs can range from $50 (gas cap) to over $1,000 (catalytic converter). This cuts into your profit.
• Time and effort: Diagnosing and fixing the problem takes time. You’ll need to visit a mechanic, possibly wait for parts, and retest the system.
• No guarantee of higher offer: Some buyers may still negotiate aggressively, knowing you’ve already invested in repairs.

When It Makes Sense to Repair

Consider repairing the issue if:

• The fix is inexpensive (under $200)
• The car is otherwise in good condition and you want top dollar
• You’re selling to a private buyer who will require a smog check
• You’ve already had the car scanned and know the exact problem

When It Might Be Better to Sell As-Is

Selling without repair might be the better option if:

• The repair cost is high and would erase most of your profit
• The car is older or has high mileage, and you’re okay with a lower sale price
• You’re selling to a dealer or junkyard that doesn’t require a smog check
• You’re in a hurry to sell and don’t want to deal with repairs

Example Scenario

Let’s say you have a 2012 Honda Civic with 120,000 miles. The check engine light came on, and a free scan at AutoZone shows code P0420—catalytic converter efficiency below threshold. A mechanic quotes $1,200 to replace the converter.

If you repair it, you might sell the car for $6,000. If you sell it as-is with the light on, you might get $4,500. After repair costs, your net is $4,800—only $300 more than selling as-is. In this case, repairing might not be worth it unless you can find a cheaper solution or the buyer insists on a working vehicle.

How to Disclose the Check Engine Light When Selling

If you decide not to repair the issue—or even if you do—you must disclose the check engine light to potential buyers. Transparency builds trust and protects you from legal trouble.

Written Disclosure

California law requires that disclosures be made in writing. When completing the **Bill of Sale** (REG 138), you should include a statement such as:
“Seller acknowledges that the check engine light is currently illuminated. The cause has not been diagnosed or repaired. Buyer accepts the vehicle in its current condition.”

You can also use a separate disclosure form or add notes to the title transfer document. The key is to make it clear that the buyer is aware of the issue.

Verbal Disclosure

While written disclosure is legally required, it’s also a good idea to mention the check engine light during conversations with potential buyers. Be honest about what you know—whether you’ve had it scanned, what the code was, or if a mechanic looked at it.

For example:
“The check engine light came on last week. I had it scanned, and it showed a P0171 code—system too lean. I haven’t had it fixed yet, but I can share the report with you.”

This level of detail shows you’re not hiding anything and helps the buyer make an informed decision.

Providing Documentation

If you’ve had the car scanned or repaired, provide copies of the diagnostic report or repair invoice. This adds credibility and helps the buyer understand the scope of the issue. Even if you haven’t fixed it, showing that you’ve taken steps to diagnose the problem can ease concerns.

Selling “As-Is” Doesn’t Mean “Hide the Truth”

Many sellers think that labeling a car “as-is” gives them a free pass to hide problems. That’s not true in California. Selling “as-is” means the buyer accepts the car in its current condition—but only if they know what that condition is. You still have a legal duty to disclose known defects, including a lit check engine light.

Failing to disclose could result in the buyer rescinding the sale or suing for damages if the problem turns out to be serious.

Tips for Selling a Car with the Check Engine Light On

Selling a car with a warning light can be challenging, but with the right approach, you can still get a fair price and close the deal smoothly. Here are some practical tips to help you succeed.

1. Get a Diagnostic Scan

Even if you don’t plan to fix the issue, get the car scanned. Most auto parts stores like AutoZone, O’Reilly, or Advance Auto Parts offer free OBD-II scans. Knowing the trouble code gives you valuable information to share with buyers and helps you explain the issue accurately.

2. Be Honest and Upfront

Don’t downplay the problem or pretend you don’t know why the light is on. Buyers appreciate honesty, and it reduces the risk of disputes later. If you’re unsure of the cause, say so—but emphasize that you’re disclosing it openly.

3. Price the Car Fairly

A car with a check engine light will sell for less than one without. Research similar vehicles in your area using sites like Kelley Blue Book, Edmunds, or Craigslist. Adjust your asking price to reflect the known issue. For example, if comparable cars are listed at $7,000, you might price yours at $5,500–$6,000 with full disclosure.

4. Target the Right Buyers

Some buyers are more willing to take on a project car. Mechanics, car enthusiasts, or people looking for a cheap commuter vehicle might be interested—especially if the issue is minor. Consider listing on platforms like Facebook Marketplace, Craigslist, or local car groups where you can explain the situation in detail.

5. Offer a Repair Credit

Instead of fixing the issue yourself, you can offer a repair credit at closing. For example, “I’ll reduce the price by $300 so you can have the oxygen sensor replaced.” This gives the buyer flexibility and shows you’re willing to work with them.

6. Keep Records

Save all documentation related to the check engine light—scan reports, repair estimates, emails with buyers, and signed disclosure forms. These records can protect you if a dispute arises after the sale.

7. Consider a Pre-Purchase Inspection

Encourage serious buyers to have the car inspected by their own mechanic. This builds trust and gives them peace of mind. If the inspection confirms the issue is minor, it could actually help close the sale.

What Happens After the Sale?

Once you’ve sold the car, your responsibilities don’t end. California law requires you to notify the DMV within five days of the sale using the **Notice of Transfer and Release of Liability** (REG 138). This protects you from liability for parking tickets, tolls, or accidents that occur after the sale.

If you sold the car with a check engine light and properly disclosed it, you’re generally not liable for future repairs—even if the problem worsens. However, if you failed to disclose the issue or lied about the car’s condition, the buyer could potentially take legal action.

Can the Buyer Come Back to You?

In most cases, no—especially if you sold the car “as-is” with full disclosure. California’s “as-is” sales mean the buyer accepts the vehicle with all its flaws, provided they were informed. However, if you misrepresented the condition or concealed known problems, the buyer may have grounds for a claim.

Final Thoughts

Selling a car with the check engine light on in California is entirely possible—but it requires honesty, preparation, and a clear understanding of the rules. By disclosing the issue, pricing the car fairly, and following state regulations, you can sell your vehicle legally and ethically. Whether you choose to repair the problem or sell as-is, transparency is your best tool for a successful sale.

Frequently Asked Questions

Can you legally sell a car with the check engine light on in California?

Yes, it is legal to sell a car with the check engine light on in California as long as you disclose the issue to the buyer in writing. However, the vehicle must still meet smog check requirements if applicable.

Will a check engine light cause a smog check failure in California?

Yes, a lit check engine light will result in an automatic smog check failure. The OBD-II system must show no active codes and all readiness monitors must be set for the test to pass.

Do I have to fix the check engine light before selling my car in California?

No, you are not required to fix the issue before selling, but you must disclose it to the buyer. Repairing it can help pass smog and increase the car’s value.

Can I sell a car “as-is” with the check engine light on in California?

Yes, you can sell a car “as-is” with the check engine light on, but you must still disclose the issue in writing. Selling “as-is” does not exempt you from disclosure laws.

What happens if I don’t disclose the check engine light when selling?

Failing to disclose a known issue like a check engine light can be considered fraudulent misrepresentation. The buyer may have legal grounds to rescind the sale or seek damages.

Can a buyer return a car after purchase if the check engine light was disclosed?

Generally, no. If the issue was disclosed and the car was sold “as-is,” the buyer accepts the vehicle in its current condition and cannot return it solely because of the check engine light.