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Home >> Cadillac >> 1998 >> Catera >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0300 - Engine Misfire Detected >> Diagnostic Procedures
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  , then go to next step.
  2. If DTCs P0201-P0206 are also set, go to applicable DTC. If DTCs P0201-P0206 are not present, go to next step.
  3. If DTC P1460 is set, go to step 5). If DTC P1460 is not set, go to next step.
  4. If DTCs P0301-P0306 are also set, go to applicable DTC. If DTCs P0301-P0306 are not present, go to step 8).
  5. Using scan tool, monitor fuel level volts. If reading is greater than 6.8 volts, go to next step. If reading is less than 6.8 volts, go to step 8).
  6. Add 5 gallons of fuel to fuel tank. If fuel level volts is less than 6.8 volts, go to step 14). If fuel level volts is greater than 6.8 volts, go to next step.
  7. Repair fuel sending unit or circuit problem. After repairs, go to next step.
  8. Start and idle engine. Using scan tool, monitor all misfire current counters (6 counters, one per cylinder). If any misfire current counters increase, go to next step. If any misfire current counters do not increase, go to step 10).
  9. Inspect vacuum hoses for splits, kinks and proper connections. Check throttle body and intake manifold for vacuum leaks. Check PCV valve operation and system for vacuum leaks. Ensure ECM grounds are clean and secure. Ensure all injector harness connectors and spark plug wires are installed at correct locations and secure. Repair as necessary. After repairs, go to step 14). If all components and systems are okay, go to step 11).
  10. Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0300 is set, go to next step. If DTC P0300 is not set, see DIAGNOSTIC AIDS.
  11. Using DVOM, check resistance of spark plug wires at cylinder(s) which indicate misfire. If resistance is greater than 10,000 ohms, replace wire(s) as necessary. After repairs, go to step 14). If spark plug wires are okay, go to next step.
  12. Remove spark plug(s) as necessary and inspect for signs of oil or coolant fouling. Replace spark plug(s) or repair engine as necessary. If spark plugs are okay, go to next step.
  13. Check spark plugs for cracks or damage, excessive wear or improper gap. Check for carbon tracking on insulator. Replace components as necessary. After repairs, go to next step. If components are okay, see DIAGNOSTIC AIDS.
  14. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0300 is set, go to step 2). If DTC P0300 is not set, go to next step.
  15. If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.
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