Diagnostics
Q: What is the check engine light?
A: The check engine light or "Malfunction Indicator Lamp" (or MIL as it is called today) is supposed to alert the driver when a problem occurs in the engine control system. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash. Some types of intermittent problems will make the lamp come on only while the fault is occurring. When the problem goes away, the lamp goes off. Other types of problems will turn the light on, and it will remain on until the fault is diagnosed and repaired.
Diagnostics
Since the earliest days of full-blown computerized engine-control systems, there has always been some type of built-in self-diagnostic capability to detect faults. A computerized engine control system uses inputs from a wide variety of sensors and switches to regulate spark timing, fuel delivery and other emission functions. If a sensor fails, reads outside its normal range of values or can't send its input back to the computer because of an open or shorted circuit, it can alter engine performance and emissions.
The computer has to have accurate inputs to make the right commands and keep things running smoothly. Likewise, the computer has to be able to carry out its command functions and send its instructions to the ignition module, fuel injectors and other control devices. If the proper commands can't get through, that too will cause problems. Monitoring the operation of the various inputs and outputs is what on-board diagnostics is all about. When computerized engine controls went nationwide in 1981 to comply with federal emission regulations, the "Check Engine" light became a new feature on the instrument panel.
Today's emission testing uses a scan tool to check if the Check Engine lamp is on, and if the light has been tampered with and if this is the case they fail you. Whenever the Check Engine light comes on, a "diagnostic trouble code" (DTC) is also recorded in the on-board computer's memory that corresponds to the fault. Some problems can generate more than one fault code, and some vehicles may suffer from multiple problems that also set multiple codes.
What's included in our diagnostic service
- Check for active or stored fault codes
- Check potential contributory systems against manufacturer specifications, including fuel pressure, fluid levels, charging system.
- Check for pertinent Technical Service Bulletins (TSB's) as listed by the manufacturer
