Check Engine Warning Light

What Is The Engine Management System

The engine management system on a modern motor vehicle comprises of an Electronic Control Unit(ECU), sensors and actuators that control operation of the engine and the emission control system. Together they control the fuel metering, ignition timing and valve timing to ensure the engine runs as efficiently and cleanly as possible. It is a very complex system that is networked with other ECU's in the vehicle including the Transmission, ABS, Instrument Cluster, Immobilser and Body Control Module.

What Is The Check Engine Light

The Check Engine Light in the instrument panel is the drivers indicator that something is wrong with the engine management system. Like most ECU's it does a self check when the ignition is turned on. The check engine light will stay on until it has completed it's self check and will go out if it does not detect anything wrong. If it does it will turn the check engine warning light on and will record a fault code. Most modern cars, but not all, have two types of diagnostic software programmed into their engine managment system. Proprietry factory software from the manufacturer and mandated software from either the USA, OBD or OBD2 (On Board Diagnostics) or E-OBD from Europe. The ODB2 protocol alone has over 15000 fault codes listed.

When The Check Engine Light Comes On

The check engine light can come on and stay on, or flash on while driving. This indicates that the ECU has picked up a fault and recorded a fault code. The first step is plug a scan tool into the cars diagnostic port. The fault codes can be downloaded and sometimes engine data recorded when the fault occured. The fault codes recorded will usually indicate the circuit or subsystem that fault has occured in. The system is then tested with diagnostic test equipment until the fault is located and the part repaired or replaced.

Fault Diagnosis and Repair

The next stage is find exactly where the fault is in the faulty circuit or whether it is a mechanical fault. This usually involves using specialised test equipment, once located the faulty part can be replaced or the faulty wiring repaired. At Khandallah garage we have the skilled technicians and training to diagnose and repair check engine light problems. We use advanced automotive oscilloscopes and gas analysers along with other specialised text equipment to trace faults on most makes of motor vehicles.

Misfires and Running Rough

Intermitant misfires are common on modern cars with multiple coils. Misfiring cars do not often set a fault code. It is common practice within the industry to replace all coils and sparkplugs, at a large expense to the customer, because of the difficulty isolating the misfiring cylinder. At Khandallah Garage we used specialised equipment to isolate the misfiring cylinder so that only the faulty part needs to be replaced. Quick, easier and much cheaper than blanket replacement of all parts. Contact us for more details.