Due the sophistication and complexity of the systems on these vehicles, the testing a non-professional can accomplish is limited. The factory recommends their special tools and test equipment for even the most basic testing. These tools, such as a Tech 1® or equivalent scan tool, take advantage of the On-Board Diagnostic capability built into the Powertrain Control Module (PCM), reading out Diagnostic Trouble Codes (DTCs) that will point the technician in the right direction. A scan tool also taps into the PCM's data stream, giving the technician a wealth of information on voltages, resistances, engine speed, temperatures and much more. Their data capturing capabilities can greatly assist in detecting difficult-to-find intermittent problems. With labor rates in most areas well over a dollar-per-minute, quick, efficient and accurate diagnosis is in everyone's best interest.
Early in the factory testing procedures is a requirement to check for factory-issued Technical Service Bulletins (TSBs), service newsletters and factory training material. This allows the factory to get up-to-date service and testing information to their technicians, much of it based on warranty claims which may show a trend, such as a weak or defective component that should be checked first. Such information and the factory testing tools are just not available to the non-professional.
One factory recommendation that makes particularly good sense is to Verify The Complaint. Is there really a problem or a misunderstanding on the part of the vehicle operator of how a system should operate- Another recommendation is to start with a thorough Visual Check. Some of the items to look for include:
All of these are things that should be checked on a regular basis and especially if there is a problem.
Secondary Spark Test
Except 3.5L Engine
One test that can be performed is checking for spark at the plugs. This is an old test, especially when checking on a Will Crank But Won't Start condition. The question has always been, 'Is the trouble in the fuel system or in the ignition system-' If there is a healthy spark at the spark plug, it can be assumed (but not guaranteed) that the problem is in the fuel system. The new twist is that with the high power ignition systems in use today, great care must be used. An older electrical system, if allowed to, might give you a shock as a reward for inattentive work. Today's electrical systems with 40,000 volts or more available to the spark plugs, could cause cardiac arrest, if mishandled.
- Locate and remove the fuel injection fuse from the underhood electrical center. This will keep the fuel system from spraying fuel into the engine when cranking the engine over with the starter.
- Install a spark plug tester. GM recommends their tester J 26792. This is similar to a spark plug with a wide gap and an alligator clip fastened to its metal shell. Similar spark plug testers are available at most auto supply stores. Connect the alligator clip to a good engine ground. Disconnect one spark plug wire and plug it onto the tester.
- Crank the engine while observing the spark tester. A crisp, blue spark should be observed.
- If a healthy spark appears, reconnect the spark plug and install the fuel injection system fuse. It can be assumed the ignition system is in good condition.