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 Check Engine light (FREE scan for trouble codes 1996 and up vehicles only   Diagnostic charges may be additional )San jose,CA
  Akin's Auto Repair

What's behind that check engine / service engine soon light, engine codes, OBD II

Why my Check Engine light comes on?

All modern vehicles have a computer or ECM (Electronic Control Module) that controls the engine operation. The main purpose of this is to keep the engine running at top efficiency with the lowest possible emissions. With today's strictest emission regulations it's not very easy to achieve - the engine needs to be constantly and precisely adjusted according to various conditions such as speed, load, engine temperature, gasoline quality, ambient air temperature, road conditions, etc.
How it basically works:
There is number of sensors that provide the ECM with all necessary inputs such as the engine temperature, ambient temperature, vehicle speed, load, etc. According to these inputs, the ECM makes initial adjustments adding or subtracting fuel, advancing or retarding the ignition timing, increasing or decreasing idle speed, etc. There is a primary (upstream) oxygen sensor installed in the exhaust before catalytic converter that monitors the quality of combustion in the cylinders. Based on the feedback from this oxygen sensor the ECM makes fine adjustment to the air-fuel mixture to further reduce emissions.
There is another, secondary (downstream) oxygen sensor installed after catalytic converter in the exhaust that monitors catalytic converter's efficiency.
Besides, there are few additional emission control related vehicle systems. For example, there is an Evaporative system (EVAP), designed to prevent gasoline vapors from the gas tank from being released into the atmosphere. It also contains number of sensors and actuators controlled by the ECM.
The ECM has self-diagnostic capability and constantly tests operation of sensors and other components. When any of the sensor signals is missing or out of normal range, the ECM sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECM memory. The same will happen if a mechanical component of controlled system fails. For example, if the EGR valve fails, this will also cause the "check engine" light to come on. Even a loose gas cap will cause the "check engine" to come on.
The stored trouble code can be retrieved with the special scan tool by the technician at Akins Auto Repair . The code itself does not tell exactly what part to replace, it only gives a direction where to look for - the technician has to perform certain tests specific for each code to find the exact cause of the problem. 

Q: What to do if my "check engine" light is on?

A: The simplest way is to visit Akins Auto Repair  for proper diagnostic. We have all the equipment and information needed to correct the problem. The problem might be even covered by the manufacturers warranty and repaired free of charge.




Q: Is it safe to drive if my check engine light is on?

A: It really depends what code is stored and what caused it. In worst cases driving with check engine light may cause more damage to the vehicle. A car may even stall while driving. If your check engine light came on, I'd certainly recommend to visit Akins Auto Repair as soon as possible, just to be on a safe side.


Q: Will disconnecting the battery reset check engine light?

A: Disconnecting the battery might reset the check engine light on some cars. Hovewer, instead of doing so, I recommend to bring your car to Akins Auto Repair  for a proper diagnostic, and here is why:
- not all cars will clear the code after disconnecting the battery
- often, the problem may be actually covered by the warranty and repaired free of charge by your dealer. For example, if you have the code P0420 - Catalyst System Efficiency Below Threshold it's very possible that your catalytic converter it's still covered by the original emission warranty and may be replaced free of charge (would cost you close to $1000 otherwise).
- some problems, if not repaired in time may cause a serious damage and more costly repair.
- disconnecting the battery will cause many other basic settings of the vehicle's computer to be erased (e.g. idle settings, fuel trim settings, transmission shift points, etc.)
- the radio, if code-protected, may be locked after disconnecting the battery
- the "check engine" light will come back anyway if the problem still exist.