Computer diagnostics -- what are they? how are they done, and what do they cost. Most cars have some form of a computer to operate the performance system. Computers have evolved in recent years, so there are any number of operating systems running from primitive to very high tech depending on the age of the car.

What are computer diagnostics? Computers generate signals called data streams. These streams of data flow through the operating system of the car at all times, constantly adjusting and re-adjusting the engine. Diagnostic computers that are interfaced with the car's computer read the data streams flowing through the system. When a problem with a computer-controlled car crops up, it shows up either in the form of a drivability problem or a lit check-engine light on the dashboard. The problem could be in the form of a bad sensor, malfunctioning electrical or mechanical component, or damaged wiring and plugs. The system is designed to generate a trouble code when it "sees" a problem in the system. This code is supposed to lodge in the onboard computer's memory for retrieval at a later date, aiding in diagnostics. The shop must have access to information either in book form or online to decipher what the codes mean and how to go about diagnosing the particular problem area. Sounds simple right? Hook the car up to "Da Machine" and it will tell you what's wrong -- hold on, not so fast, it's not that easy! What happens when there is no evidence of a trouble code stored in the car's computer and no check-engine light is lit, but a drivability problem still exists? This is where the men are separated from the boys in the world of onboard computer diagnostics.

How are computer diagnostics performed? Effective computer diagnostics and repair demands state-of-the-art equipment, cutting edge training, and up-to-date information.

Equipment: Cars of the 90s can't be fixed with 1968 equipment. Necessary equipment for the diagnostician includes:

Oscilloscopes and lab scopes to read wave patterns omitted by sensors

DVOM (Digital Volt-Ohm Meters) to measure electricity in minute amounts

Sensor stimulators which actuate sensors to make sure they are functioning properly

Diagnostic computers to read the data streams of the car's performance system

Training:
All the latest equipment is worthless without a trained diagnostician. Today's diagnosticians must keep abreast of rapidly-changing technology to remain in the field. The average student coming out of a technical college needs two years to get "up to speed" after joining the workforce.

Information: Diagnosticians must have access to over a million pages of technical information to fix computer-related problems. Transmissions, ABS brakes, HVAC (Heating Ventilation and Air Conditioning), Traction Control, Fuel Delivery Systems, and Performance Systems are all computer-controlled. Car manufacturers and vendors are constantly coming out with TSBs (Technical Service Bulletins) alerting the diagnostician of repair strategies and fixes for computer glitches.

The technician takes the tools, training, and information and diagnoses your car's problem. The diagnosis may start with a basic check of the computer's memory for any stored codes. In a perfect world, there are codes and the simple replacement of a sensor is all that is needed. But what is there are no codes!? Now the quest starts! The technician might perform a "flight test," hooking the car's performance system up to a handheld computer and test driving the car, monitoring the data stream for anything out of the ordinary. Hopefully the problem will show up in the form of a code or poor reading of a particular function. Next a "sensor stimulator test" might be in order. The car is hooked up to a machine which stimulates all the sensors, simulating the car driving down the road. Maybe a check of a particular component's electrical value with a digital volt-ohm meter is in order to see if it's operating within manufacturer's specifications.

By Tom Torbjornsen