The Check Engine Light is also known by the acronym MIL, meaning Malfunction Indicator Light. The Check Engine Light is a yellow indicator light that tells you something is wrong with the car. Although you hear the word “engine”, the Check Engine Light also comes on in response to issues with: transmission, steering system, ABS brakes, traction control, stability control, alarm system, radio, air conditioner, and window control. Most likely however, the Check Engine light is on for an engine related problem. The car must be scanned using a laptop with VAG COM or other software, factory scan tool or an OBD II code reader to retrieve the Diagnostic Trouble Codes or DTC’s. The MIL comes on for the following “engine” related issues:
Misfires from coils, spark plugs, mixture or compression. Oxygen sensor failure from age or heater resistance (OXS). Catalytic converter efficiency (CAT). Fuel vapor leakage or system malfunction (EVAP). Secondary air injection system failure to blow air into the exhaust when needed (SAI). Exhaust gas recirculation (EGR). Fuel to air ratio or mixture. Idle control malfunction. Sensor or system malfunction: including mass air flow (MAF), manifold absolute pressure (MAP), coolant temperature, air temperature, oil temperature, fuel temperature, knock sensors, vehicle speed, fuel level, exhaust pressure and fuel pressure. Camshaft position in relation to crankshaft. Turbocharger malfunction. Throttle position control. Accelerator pedal control. Brake and/or clutch switches. Intake manifold flap motor. Coolant fan control. Injectors.
The MIL can be on for other reasons besides the engine. Briefly, those are most commonly transmission issues and certain ABS problems, occasionally for a stereo, alarm system or climate control. A full explanation would take a week or so.
What to do if your Check Engine Light comes on
Depending on the model, if the Check Engine Light is blinking, the issue is likely to damage the engine, so stop driving as soon as possible. Older models don’t have that feature. Should you have a diesel Tdi, a blinking Glow Plug light also indicates a potential damage issue. If the Check Engine Light comes on steady, use all your senses to see if you feel vibration, power loss, strange smells, unusual noises or erratic shifting. If the car seems to be functioning normally, you might be able to keep going, but you NEED to know what trouble code has come up. If you detect something wrong, are not sure, or simply cannot tell, towing may be in order. Better not to risk a huge repair bill trying to save a needed tow bill. See our Karmakanix webpage on Towing Services for assistance.
Call us for good advice. We may be able to help you determine if the car is drivable or should be towed. You should come in for at least a drive-by free code reading session. Our Service Advisors can scan your computers and get the trouble codes, then advise you on the proper course of action, no charge. Understand that this is NOT diagnosis, but we can then accurately tell you what diagnostic procedures will be necessary for our technicians to determine the repairs required.
Many customers have their own basic scan tool, also known as an OBD II Code Reader. Such readers cost from $20 to $80, and up. There are also Bluetooth dongles available with apps for your phone that can read codes and give readings and/or graphs of engine functions. Dongles can be even cheaper. Whether or not the customer can understand the code is not the point. Just having the P code is worth gold. We appreciate having the DTC P code as a place to start our conversation about the needed diagnosis to isolate the problem. A P code can also help us give advice about whether the car can be driven or not. Please understand that our equipment may well divulge more codes than your scanner. And these scanners generally cannot query other ECU’s on your car other than the engine and maybe transmission, and there are 5 to 40 more ECU’s.
The OBD II connector is located under the dash within a foot or so of the driver’s left knee. Most are pink and immediately visible. Last century, manufacturers had a heyday hiding the OBD II connector in the console or dash, likely under a cover. All OBD II connectors are within 3 feet of the driver. Cars built before 1996 vary in location, and generally have two small connectors, one black and one white. These connectors are generally near the firewall, but may not be inside the car. A personal scan tool is unlikely to be able to communicate with OBD I or earlier cars. OBD I protocol covers model years from 1993 to 1995. Diagnostic systems from 1986 through 1992 are proprietary, and sometimes just lie.
Mechanics seem to think that every driver has seen the light. Probably because we fix so many cars at Karmakanix for the Check Engine Light issue, even we assume it is commonplace. The reality is different. Most drivers are caught by surprise when any warning light comes on, and not that many customers have seen a yellow one go on. Don’t let some mechanic convince you that it is OK to continue to drive with the Check Engine Light on. Often that translates that said mechanic is unable or unwilling to diagnose or fix the problem. Most importantly, some long term damage could be occurring that might cost you big, like a catalytic converter. And also, you would have no way of knowing if some other dire problem arises. As a car gets older, the likelihood increases that something will go wrong. Only a handful of problems can be temporarily left unattended for financial reasons, but you must sort out the issues to pass your next smog test.
The Check Engine Light is not any kind of mystery to our technicians. The vast majority of the diagnosis we do for an MIL, we have done a hundred times. In descending order, and depending on the model, most of them fall in this line: Secondary Air Injection. Misfires. Oxygen Sensor. Temperature Sensor. EGR control. Fuel Pressure. Catalytic Converter. Most of the cars with Misfire or Fuel Pressure faults should not be driven. And of course, this is not a complete list.
At Karmakanix, we have a constant training policy. Our technicians go to schools way past dealer training classes. And they come home with the goods to prove it. We stay current on each new fuel injection system. Between the training, our experience and the equipment at our shop, we can always diagnose any issue whether the Check Engine Light came on or not. Our Service Advisors also have similar training, and a long background in the automotive field. They can explain the problem for you in simple language. And make sure the repairs proceed efficiently.
Check Engine Lights and Smog Tests
To pass a smog test in California the car must not only pass emissions and systems checks. The Check Engine light must work when the key is turned on, and it must not be on with the engine running. Furthermore, the smog test includes scanning your engine computer (ECU) for Readiness Codes. Do not confuse these with the diagnostic trouble codes (DTC). Readiness Codes are the results from the 8 emissions related self tests that your car’s computer perform each time you start and drive your car. In order, the Readiness Codes are: Exhaust Gas Recirculation, Oxygen sensor heating, Oxygen sensors, Air Conditioner, Secondary Air Injection, Evaporative Emissions System, Catalytic Converter Heating, and Catalytic Converter Status. These Readiness Codes are seen on our scan tools as a string of 8 bits, or Zeros and Ones. A Zero means the system passed, a One means the system failed. The smog test station wants to see 0000 0000.
There are many more diagnostic tests performed that set the Diagnostic Trouble Codes (DTC), but these Readiness Codes are checks of the emission systems related to a smog test. Whenever a repair has included clearing DTC’s, the Readiness Codes are all set to 1. The car must be driven for a while until all the driving conditions have been met for the Readiness Tests to perform themselves and reset the corresponding Readiness Codes to 0 before it will pass a smog test. Alternatively, our technicians can manually run the Readiness Test procedures to set the Readiness Codes back to 0’s, then the car can go for a smog test.
At Karmakanix, we have a business relationship with 15 Minute Smog at 2598 Sacramento St, Berkeley, CA 94702, which is on Sacramento between Blake and Parker. They do one free retest, and work with us if some problem arises.