How to Troubleshoot the Ignition System in a GMC Sierraby eHow Cars Editor; Updated November 07, 2017
Items you will need
Spark plug gapping tool
Ignition Coils in a Distributor System<p>Turn off your Sierra's ignition switch before you begin. Tag the spark plug wires to indicate which cylinder they connect to, then disconnect them from the ignition coil.</p>
Ignition Coils in a Distributorless System<p>Connect a scan tool to the Sierra's Data Link Connector. This should be located below the dash on the driver's side.</p> <p>Download the diagnostic trouble codes from the scan tool. Read all the instructions with the device and follow then properly to get these codes.</p> <p>Look for a code matching an ignition coil problem. P0351 through P0358 indicate problems with a coil control circuit. P1351 means high voltage and P1361 means low voltage.</p> <p>Check the wiring before you replace the ignition coil. Look for short circuits, broken or chafed wires, loose connections or corroded terminals.</p>
Spark Plugs<p>Inspect the insulator surrounding the plugs, checking for cracks. Cracks usually occur where the porcelain insulator meets the shell (where the plug begins spreading out toward its widest point).</p> <p>Clean the plugs of any dirt or corrosion. You can use a stiff brush, but taking it to a shop with an available spark plug cleaner works better.</p> <p>Look over the gap between the side and center electrodes. The side angle should be parallel to the center one. Use a spark plug gapping tool to measure the gap and bend it if needed.</p>
The affected coil control circuit matches the last digit on the code. P0351 means a problem with Ignition Coil 1, while P0354 indicates Coil 4.
Don't bend used spark plugs if the Sierra uses platinum ones. Spark plugs are easy and inexpensive to replace.