One of the basic means of letting you know all is not right within your car’s many systems is that little yellow light that pops up on the instrument cluster which urges you to “Check Engine” or “Service Engine Soon”. Often drivers will ignore this message, especially when the vehicle seems to be going down the road just fine. Many times they will seek advice from friends, family members or self-proclaimed experts who “used to be a mechanic”.
The truth is that there may be several hundred reasons that the warning light illuminates, depending on the make, model and year of the car or truck. Sometimes it points to tightly controlled emissions readings which are elevated above normal. Some deal with critical sensors that control the ignition and fuel injection system . Some may relate to a transmission problem. There is a method which trained auto technicians use to pin down the exact problem. They first use an electronic scan tool to read the message, in code form, sent by the car’s sensors to the on-board computers . They then access information about the specific system and perform electronic tests to pinpoint the cause of the sensor’s message.
Many car owners today have access to simplified scan tools which are called code-readers. Your local parts store may use one to guide do-it-yourself car owners towards buying a part or sensor to fix the cause of the dash light.
Therein lies the problem – the sensor that turns on the light is telling you that it senses a problem with fuel mixture, ignition timing, specific emission control device functions, transmission shift points and many other possible “parameters ” of the engine control module (ECM) programming.
The sensor is only the messenger, the real culprit maybe a too-lean fuel mixture caused by broken vacuum hose, a too-rich mixture caused by a stuck-open thermostat, a piece of metallic dirt picked up from the road on a crank timing sensor, a misfire caused by a bad coil, a connector or a spark plug, an exhaust gas recirculation valve (EGR) with carbon-plugged passages or one of many other failures that have nothing to do with the integrity of the sensor itself.
Yet the tendency in untrained auto repair is to “Shoot the Messenger”, an oxygen sensor, a coolant temp sensor, a cam position sensor, a throttle position sensor etc. These electronic sensors are usually nonrefundable parts when purchased and installed … and often the check engine light returns the very next day. The car owner still has an unidentified problem as well as an out of pocket expense of a hundred dollars or more! It is always best to have these warning light issues first checked by a professional automotive electronics technician. When looking for the right shop, check for ASE Blue Shield certified techs. AAA approved auto repair and other professional associations which mandate and improve the training level and skills of the technicians.
Jim O’Neill
Chino Autotech Inc.,
Auto Club of SoCal Approved Auto Repair Facility
Auto Value Certified Service Center
NASTF Service Information/Communications Committees
ASE Certified Master Auto Technician-Advanced Level, CA. Licensed Smog Check Technician-46 years
AMI AAM Accredited Automotive Manager, Member SAE International SoCal Section
Northwood University-University of the Automotive Aftermarket-Leadership 2.0, Class of 2008-2009