Diagnostic trouble engine codes (or fault codes) are codes that are stored by the on-board computer diagnostic system.

These engine codes are stored when a sensor in the car reports a reading that is outside the normal.

These engine codes identify a particular problem area.  Consequently, They are intended to provide the technician with a guide as to where a fault might be occurring.

Engine codes should be used in conjunction with the vehicle’s service manual. As a result, They will help you discover which systems, circuits or components should be tested.

Engine Codes
Engine Codes

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Car code reading and scanning sound simple, right? Well, there’s more to it than that. A code that indicates your oxygen sensor is “lean” can mean the sensor is dead, or it can mean that the air/fuel mixture really is lean and you’ve got either a vacuum leak or a fuel problem.

Now you have a better idea of what makes up a DTC (Diagnostic Trouble Code). You can see that every digit has it’s purpose. You also know which system is having the problem just by knowing what the first few numbers are.

So what are the most common reasons the check engine lights come on?

  • Faulty O2 sensor: The oxygen sensor measures how much fuel is being burned and whether it’s too little or too much.
  • Loose or damaged gas cap: Usually fixed by getting a new gas cap. Easy fix.
  • Bad catalytic converter: Costs an average of $2000 to fix. Pricey, let’s hope you don’t have this one.
  • Problem with the mass airflow sensor (MAF): Could cost an average of about $375 to fix.
  • Spark plug problems:  The fix can range from $20 for someone who can DIY it, or quite a bit more at a shop. If you neglect this one, it could lead to problems with the catalytic converter.

Also, Most auto parts stores will check the OBD-II PID service codes, and will do it for free.