Dieseling, Run-On

Engine continues to run after key is turned to the Off position, but runs very rough. (If engine runs smooth, check ignition switch.)
^ Check:
^ Fuel injectors for fuel leakage.
Perform a fuel system operational test at the pressure test connector. Refer to "Fuel System Diagnostics." Component Tests and General Diagnostics

Fuel ignites in intake manifold or in exhaust system, making a loud popping sound.
^ Check:
- EGR for valve not opening - refer to EGR valve DTC P0401, P0402, P0404, P0406, and EGR valve replacement in exhaust.
- Intake manifold gaskets for leaks.
- Misfiring, cross firing or cutting Out under load.
- Spark plugs. Check for wetness, improper gap, cracks, burned electrodes and heavy deposits.
- Ignition coil connections.
- Ignition system for moisture, dust, cracks, burns, etc.
- ECM and ignition system for faulty grounds.
- Secondary ignition voltage output with service tool SA9199Z tester.
- Engine valve timing and compression.
- Worn or incorrect basic engine parts such as camshaft(s), heads, pistons, rocker arms, lifters, broken or worn valve springs, etc.