Blog Car Care Advice Top 11 Causes of the Subaru Check Engine Light (+ Next Steps)
Car Care Advice

Top 11 Causes of the Subaru Check Engine Light (+ Next Steps)

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The Check Engine Light on your old or new Subaru can indicate various problems, from minor to significant issues. However, knowing the possible causes can help you decide between a DIY fix or consulting certified technicians. 

So, what triggers it?
And what steps should you take?

Let’s explore the common Subaru Check Engine Light causes, diagnosis, and associated costs.

This Article Contains: 

Let’s go.

11 Reasons Your Subaru Check Engine Light Has Come On

There’s a chance of unforeseen problems in both old and new vehicles. Fortunately, cars can inform you before certain issues cause major damage by activating the Check Engine Light (CEL). 

Here are a few causes for this dashboard warning light:

1. Damaged, Missing, or Loose Gas Cap

A damaged, missing, or loose gas cap (AKA fuel cap) is a common reason for an activated Check Engine Light. Without a secured gas cap, fuel vapors escape into the air, causing reduced fuel economy and a distinct gasoline smell. The car’s emissions control system notices the problem and turns on the Check Engine Light.

2. Oxygen Sensor Failure 

The oxygen sensor or O2 sensor monitors your engine’s performance and emissions. A malfunctioning oxygen sensor because of age, contamination, or wiring problems can trigger the check engine warning light and related diagnostic trouble codes. It may also impact engine efficiency and your vehicle’s environmental compliance.

3. Catalytic Converter Issues 

Over time, dirt can clog and damage the catalytic converter. When this happens, the catalytic converter can’t do its job properly, increasing emissions. You may also experience reduced engine performance, poor fuel economy, and a lit Check Engine Light.

4. Faulty Ignition Coil 

The ignition coil transforms low-voltage electricity from the battery into the high-voltage current required to set off the spark plugs. If it fails, it can cause engine misfires, rough idling, and even damage its internal parts. These issues can activate a flashing Check Engine Light.

5. Bad Spark Plug or Spark Plug Wire 

The spark plug creates the sparks that ignite the engine’s fuel mix, and the spark plug wire carries those sparks from the ignition coil to the plugs. A bad spark plug or spark plug wires can mess up how the engine burns fuel, making it less efficient and increasing emissions. In such cases, the CEL might start flashing.

6. Fuel Injection System Issues 

If the fuel injection system gets clogged, leaks, or breaks, it can mess up the fuel pressure and how much air and fuel the engine gets. The Engine Control Module (ECM) notices these problems through sensors and turns on the Check Engine Light. 

7. Valve Timing Solenoid Malfunctioning

The valve timing solenoid decides when the engine’s valves should open and close for proper combustion. An overdue oil change can block the valve timing solenoid passages, leading to malfunctions and a lit check engine dashboard light.

8. Weak Battery 

A weak battery won’t provide enough voltage, leading to dim lights, erratic radio behavior, and other electrical issues. Moreover, since the ECM can’t perform proper diagnostic tests due to low voltage, it may trigger the Check Engine Light. 

9. Mass Airflow Sensor Problems 

When the mass airflow sensor malfunctions, it can feed incorrect data to the ECM, disrupting the air-fuel balance. This can result in engine performance problems and an activated check engine warning light with a related fault code.

10. Transmission Issues 

Gear slippage, torque converter glitches, or other transmission problems can disrupt engine performance and overall vehicle function. The throttle position sensor and transmission fluid sensor relay these issues to the car’s computer, triggering the CEL.

11. Engine Control Module Issues 

Subaru’s new vehicles feature state-of-the-art ECM technology, ensuring that the Check Engine Light performs precise diagnostics to detect issues promptly. If it detects a fault or malfunction within itself, it will trigger various Diagnostic Trouble Codes (DTC) and illuminate the CEL.

Note: A lit CEL may also deactivate the cruise control system. Cruise control allows a vehicle to maintain a constant, pre-set speed without the driver applying the throttle continually.

Now, let’s explore how to address a lit Subaru Check Engine Light.

What to Do When Your Subaru’s Check Engine Light Comes On? 

Here are steps to take based on the different Check Engine Light scenarios:

1. Intermittent Check Engine Light

If your vehicle’s Check Engine Light activates intermittently, try to notice any changes in your car’s performance, such as strange noises, vibrations, or reduced engine power. If you notice any performance issues, request an express service at your service center to address them before they worsen.

2. Constantly Illuminated Check Engine Light

When your Subaru’s Check Engine Light stays on constantly, it’s best to get driving directions to the nearest Subaru service center for immediate vehicle service. Ignoring a consistently illuminated Check Engine Light can result in significant problems and higher repair costs.

3. Check Engine Light with Performance Issues

Your vehicle may enter “limp mode” if you have a consistently lit CEL and performance issues like rough idling or stalling. Plus, driving extensively in limp mode can aggravate current engine issues. In such cases, promptly schedule service appointments and have the vehicle towed to prevent further engine damage. 

4. Flashing Check Engine Light while Driving

The Check Engine Light flashing, whether on an old Subaru Forester or any new Subaru model, indicates severe problems requiring immediate attention.

Carefully pull over to the side of the road, turn off your engine, and have your Subaru towed to certified technicians for an express service. If it’s outside of typical service hours, you can schedule an online appointment with a mobile mechanic who will come to your driveway to resolve the issue. 

Next, let’s review the appropriate steps for diagnosing and resolving the problem.

How to Diagnose and Reset the Subaru Check Engine Light

Here’s how certified technicians would address the Check Engine Light in Subaru cars:

  1. Turn off the engine.
  1. Connect an OBD-II scanner to the vehicle’s OBD-II port.
  1. Turn the ignition key to the “On” position, but do not start the engine.
  1. Use the OBD-II scanner to identify the check engine or fault code.
  1. Perform any necessary repairs (whether an oil change or replacing failed parts with new Subaru inventory) to address the issue.
  1. Use the OBD-II scanner to reset the CEL.
  1. Drive your Subaru to confirm that the light stays off and the issue is resolved.

Now, consulting a mechanic or Subaru service center for diagnosis comes with a price. Let’s review the estimates.

How Much Does a Subaru Check Engine Light Diagnosis Cost? 

Whether you drive a Subaru Impreza or Outback, the diagnostic fee for old and new Subaru cars ranges from $80 to $120, which covers the labor charges and equipment used to identify the issue.

Additional costs may be incurred for repairs or new Subaru inventory. The final cost depends on the service center, the underlying problem, and the required new inventory.

Here are estimates for some new inventory, excluding labor: 

Pro tip: Part replacements are common in older cars. That’s why it’s best to look at certified pre-owned inventory and pre-owned specials when buying used cars. Certified pre-owned inventory is often repaired to recreate a “like new” condition.

Final Thoughts

Whether driving a Subaru Forester or a Subaru Impreza, the Check Engine Light alerts you to certain car problems you shouldn’t ignore. 

Luckily, RepairSmith is here to help fix it right from your driveway
We’re a mobile auto repair service available seven days a week with flexible service hours. We also offer a 12,000-mile, 12-month warranty on all repairs. 

Contact us for a Subaru service today.