From 2010 to the end of 2020, I was a service writer at a car repair facility here in Central Ohio. For eight of those years, I also contributed to MOTOR Magazine, writing about shop operations. But the truth is, I’d spent a lot of time at the shop even before working there full-time. Counting back, the first day I answered the phone and helped a customer was in 2002. In any case, during the 10-year continuous stint, I probably wrote thousands of Honda Pilot, Odyssey, Ridgeline, V6 Accord, and applicable Acura orders when they came in with their dash lights aglow. Here are 10 common reasons why a Honda 3.5L V6 “check engine” light might come on.

1. Bad EGR valve

The Exhaust Gas Recirculation (EGR) valve helps reduce emissions by recirculating exhaust gases into the intake. Over time, carbon buildup can clog the valve, triggering a check engine light.

Fix: Cleaning the EGR valve might work, but often, replacement is the best solution. Expect to spend a few hundred bucks for parts and labor.

2. Faulty ignition coils

Ignition coils provide the spark that keeps your engine running. When one fails, you’ll notice rough idling, poor acceleration, or even misfires. The check engine light will usually flash if it’s bad enough.

Fix: Replacing a single coil isn’t too pricey, but if multiple coils go out, the cost can add up fast. Expect a few hundred dollars or more, depending on how many you replace.

3. Vacuum leaks

Vacuum leaks occur when unmetered air enters the engine, throwing off the air-fuel mixture. Cracked vacuum hoses, a leaking intake manifold gasket, or a faulty PCV valve can all cause rough idling, poor acceleration, and a check engine light.

Fix: Replacing a vacuum hose or gasket is usually affordable, but diagnosing the exact source of the leak can take time. Expect repair costs to vary from cheap to a few hundred bucks, depending on the severity.

4. Failing VTEC solenoid

On the Honda 3.5L V6 (and others), the Variable Valve Timing and Lift Electronic Control (VTEC) system boosts performance and efficiency. If the solenoid fails, oil flow to the system gets disrupted, leading to a check engine light and reduced power.

Fix: A new VTEC solenoid isn’t too expensive, but labor can add up. Expect to pay a few hundred dollars for the repair.

5. I saw a ton of EVAP system leak codes on Honda 3.5L V6 engines

The Evaporative Emission Control (EVAP) system prevents fuel vapors from escaping. A loose gas cap, cracked hose, or faulty purge valve can cause a small leak, triggering the check engine light.

Fix: If it’s just a loose gas cap, tightening or replacing it is cheap. If the problem is deeper in the system, repairs can range from a quick fix to a few hundred dollars.

6. Dirty or Failing Mass Airflow (MAF) Sensor

The MAF sensor measures how much air enters the engine. If it gets dirty or fails, the engine may run too rich or too lean, leading to rough performance and a check engine light.

Fix: Cleaning the MAF sensor is cheap and easy. If it needs replacement, expect to spend a couple hundred bucks.

7. Bad air/fuel ratio (AFR) sensor, oxygen (O2) sensor, or catalytic converter

The AFR and O2 sensors monitor exhaust gases to help adjust fuel mixture. A failing sensor can cause poor fuel economy and sluggish performance. In some cases, a failing catalytic converter (which reduces harmful emissions) can also trigger the check engine light and may be related to a bad O2 sensor.

Fix: Replacing an O2 sensor isn’t too expensive, but a catalytic converter replacement can be very costly—often over a thousand bucks. Diagnosing whether it’s just a sensor or the converter itself is key to avoiding unnecessary expenses.

8. Misfires from worn spark plugs

Old spark plugs can cause misfires, rough idling, and poor acceleration. The check engine light often flashes when misfires are severe.

Fix: Spark plug replacement is relatively inexpensive, but labor can add up if you don’t DIY.

9. Faulty fuel injectors

Clogged or malfunctioning fuel injectors can cause misfires, hesitation, and rough running. Of all the possibilities with ignition, spark, compression, and fuel systems, I’ll say this was much less common than, say, spark plugs and coils.

Fix: Sometimes a fuel system cleaner works, but if an injector needs replacing, expect a decent repair bill.

10. Low engine oil or oil pressure issues

Low oil can trigger a check engine light, especially if it affects VTEC operation or causes timing issues.

Fix: If you’re just low on oil, a top-off is cheap. But if oil pressure is dropping due to a worn oil pump or internal engine issue, repairs can be costly. Keep in mind that running the oil low in any engine even once is very much ill-advised and can easily affect the car’s longevity.

A check engine light can mean a lot of things, but these are some of the usual suspects in Honda’s 3.5L V6. If you’re handy, some fixes are DIY-friendly. If not, a trusted mechanic can diagnose and repair the issue before it gets worse. Either way, don’t ignore that light; it’s your engine’s way of asking for help before things get too serious. Remember that if you “check engine” light starts blinking at you, pull over immediately.