Vacuum Leaks: Misfires are quite a common problem on GMC trucks. Tracing down the source of the problem can be tricky, as it usually happens sporadically. In addition to checking spark plugs and ignition coil, you should also inspect the intake for eventual vacuum leaks. Code: P0300
EGR Valve: A carbon buildup is a common cause of various EGR-related problems. While this will not affect engine performance in general, it might cause higher fuel consumption. If not too extreme, carbon buildup can be cleaned with EGR cleaner spray. Related Fault Code: P0401
Catalytic Converter: Higher mileage GMC trucks are likely to experience some emission control issues. In most cases, this is caused by a worn-out catalytic converter, especially if the truck suffered from a prolonged misfire. Another possibility is a faulty downstream O2 sensor. Related Fault Codes: P0420 and P0430
EVAP leak: TheEVAP system is a frequent failure point. In addition to faulty vent or purge valve, these problems can be caused by various EVAP leaks. Finding a leak, usually due to cracks in EVAP lines, is best done with a smoke generating machine. Related Fault Codes: P0442, P0445, and P0449.
Variable Timing Issues: Most newer VORTEC engines have variable valve timing for better performance. This system depends on good oil pressure within VVT solenoids. If oil changes are neglected, screens on these solenoids get clogged with oil sludge and other contaminants. This obstructs oil flow and throws off the timing, resulting in a lack of acceleration and hesitation. In most cases, solenoids and screens can be cleaned. Related Fault CodeP1345 (crankshaft/camshaft correlation)
With a "check engine" light on, you need to find out what caused it. You can either take your car to the workshop for a full diagnosis or get your own OBD-II scanner. Your local auto parts store may also read the codes free of charge.
OBD-II scanners come in all shapes, sizes, and prices to choose from.
The choices range from something simple as a Bluetooth OBD adapter that connects to an application on your smartphone over dedicated hand-held scan tools to powerful diagnostic tools.