Our authorized Subaru service center has seen and solved just about anything that could go wrong with a vehicle, and the check engine light is a common one. You see, today's vehicles are operated with a sophisticated computer that takes information from a variety of sensors to run the engine as efficiently as possible. If any of these sensors goes bad or sends the wrong information, the computer will turn on the check engine light. Below, we look at six of the more common reasons for this light coming on. However, determining exactly why the CEL is on in your vehicle will mean hooking the vehicle up to a code reader at an authorized service center like ours at Carter Subaru Ballard.
If you have any questions or would like to schedule an appointment to have your check engine light diagnosed, please give us a call or fill out our convenient and secure online service appointment form. The experts in our service center are always available and happy to help the greater Seattle area with all things Subaru.
 6. Spark Plug or Ignition Coil Could be Bad
The spark plugs in your engine are the workhorses of the ignition system and necessary to ignite the fuel and air mixture so the engine can run. If a spark plug isn't firing the way it's supposed to, the engine will 'miss' and that usually turns on the check engine light. The problem could be with the spark plug itself or it may be another component in the system like an ignition coil.
5. Bad Information from Mass Airflow (MAF) Sensor
An engine needs three things in precise amounts to run properly: air, fuel, and spark. The Mass Airflow Sensor is responsible for telling the computer how much air is going into the engine. If this sensor fails, the computer will not know how much fuel to add and the engine may run poorly or not at all.
 4. May Need New Exhaust Gas Recirculation (EGR) Valve
To meet stringent emission standards, most vehicles will recirculate some of the exhaust gases back through the engine. This is the responsibility of an Exhaust Gas Recirculation valve. If the EGR valve fails, the computer will recognize the problem and turn on the check engine light. This part may seem a little pricey, but it's typically an easy fix and will ensure that your engine gets back to running the way it should.
3. Could be a Loose Gas Cap
Another important part of today's emissions standards is ensuring that raw fuel isn't exposed to the environment where it can evaporate into the atmosphere. That's why the computer can detect if the gas tank isn't properly sealed and turn on the CEL if it's not. Typically, a simple tightening or replacement of the gas cap will solve this problem.
 2. Bad Catalytic Converter
Virtually every modern car is equipped with one or more catalytic converters (Cat). These are part of the exhaust system and made of material that becomes hot enough to catalyze unburnt fuel and other products of the engine's combustion. To determine if the catalytic converter is working properly, the level of oxygen in the exhaust is measured with a sensor that's either in the Cat or behind it. This is considered the downstream oxygen (O2) sensor. If this is the reason that your check engine light comes on, the problem is either a bad sensor or a bad Cat.
1. Bad O2 Sensor
Similar to the sensor that determines if the Cat is working properly, another O2 sensor is placed in the exhaust system before the Cat. This sensor sends information that the computer uses to determine if the right amount of fuel is being sent to the engine. While the downstream O2 sensor for the Cat holds no influence over how the engine is running, this upstream O2 sensor is an important part of how the computer operates the engine.
Carter Subaru Ballard
5201 Leary Ave NW
Seattle, WA 98107
- Sales: (206) 782-7475
- Service: (877) 835-5240
- Parts: (877) 884-0162
