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FAQ

Why is my check engine light on?
(For 1996 and newer vehicles)

Your check engine light only comes on when your vehicle engine computer determines that your emissions have exceeded 1.5 times the limit.

If your check engine light is:
  • Flashing while driving: this means that your car has had a type A misfire. This will cause damage to the catalytic converter. You should take your car to a service center immediately before permanent damage is done.
  • Not Flashing and vehicle runs: if there are no drivability issues, your vehicle is exceeding the limit for emissions, but unlikely you will do immediate damage. Bring your car in for service as soon as possible.

Very often the task of diagnosing the root cause of your vehicle's problem can involve the use of many different types of equipment and instrumentation. Each serves a specific function to help us accurately and effectively diagnose your vehicle's problem.

Felsing's Service has factory specific tools and software for most makes and models. We employ ASE and state emissions certified technicians trained to interpret and analyze the highly technical data the diagnostic tools provide.

WHAT MIGHT BE INVOLVED IN DIAGNOSING FAILED EMISSIONS &
COMMON CAUSES OF EXCESSIVE EXHAUST EMISSIONS

IT COULD BE ONE OR MORE PROBLEM(S)

NOTE: AFTER FAILED EMISSION TEST REPAIRS: Be sure to drive the car for awhile before taking it in for the emission test again. Computer monitors have to reset, and this resetting happens under all kinds of driving conditions.

Emission Testing Failures:

HIGH HC on DRIVING TEST/HIGH IDLE TEST

  • Vacuum leaks (hoses, EGR valve, intake manifold and carburetor)Ignition system malfunction (plugs, wires, coil)
  • Faulty computerized engine management and/or oxygen sensor
  • Internal engine problem (burned valves, poor compression)
  • Failed catalytic converter
  • Incorrect ignition timing and/or idle speed
  • EGR valve partially stuck open
  • Incorrect air/fuel mixture
  • Faulty fuel injector operation

HIGH CO on DRIVING TEST/HIGH IDLE TEST
Excessively rich mixture due to:

  • Faulty carburetor and/or malfunction
  • Dirty air filter, faulty choke
  • Faulty computerized engine management and/or oxygen sensor
  • Faulty fuel injection system
  • Faulty thermostatic air cleaner (TAC) system
  • Defective or faulty evaporative canister purge system
  • Inoperative or missing catalytic converter
  • Faulty or missing air injection system
  • Miss adjusted idle mixture
  • High fuel electric fuel pump pressure (fuel regulator fault, restricted return line)

HIGH Nox on DRIVING TEST

  • Inoperative or ineffective EGR (Exhaust Gas Recirculation) system
  • Excessive lean air/fuel ratio
  • Inoperative or missing catalytic converter (Three way catalytic)
  • Excessive spark advance
  • Faulty Thermostatic Air Cleaner (TAC) system
  • Defective computerized engine management and/or oxygen sensor
  • Engine deposits (carbon)
  • Engine mechanical defect(s)

COMMON MISSED ITEMS RELATED TO EMISSIONS

  • Dirty or contaminated engine oil
  • Plugged/non-functioning PCV system (positive crankcase ventilation) valve or filter
  • Fuel or air filter
  • Defective drive belts