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Home >> Saab >> 1999 >> 9-3 Base, 2D Convertible, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - TRIONIC T5 Fuel Control System >> Diagnostic Tests >> DTC P0300: Random Misfire Detected
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DTC P0300: Random Misfire Detected

  1. Connect TECH 2 scan tool to DLC. Turn ignition on. Check for presence of DTCs. If DTC(s) P1416, P0106-P0108, P0112-P0113, P0117, P0118, P0121-P0123, P0125, P0132, P0133, P0135, P0441, P0442, P0444, P0445, P0506, P0507 or P1171 are present, go to appropriate diagnostic test. If DTCs are not present, go to next step.
  2. Check for vacuum leaks, moisture or corrosion at MAP sensor and connector located under passenger side engine compartment brace. Inspect fuel pressure regulator hose for damage or leaks. If no problems are found, go to next step. If any problems are found, repair as necessary and go to step  12 .
  3. Use scan tool to contact TRIONIC 5 OBD II. Select TEST VALUE: COOLANT TEMPERATURE. Turn ignition on. Compare scan tool reading to actual engine temperature. If reading is close to actual temperature, go to next step. If reading is not close to actual temperature, repair or replace faulty ECT sensor or circuit. See COOLANT TEMPERATURE SENSOR (ECT) under ENGINE SENSORS & SWITCHES in appropriate SYSTEM & COMPONENT TESTING article. Go to step  12 .
  4. Use scan tool to select READING: INTAKE PRESSURE. If scan tool reading is about 102 kPa, go to next step. If reading is not as specified, repair or replace faulty MAP sensor or circuit. See MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR under ENGINE SENSORS & SWITCHES in appropriate SYSTEM & COMPONENT TESTING article. Go to step  12 .
  5. Start engine and allow it to idle. Observe READING: INTAKE PRESSURE. If scan tool reading is between 40-60 kPa, go to next step. If reading is not as specified, repair or replace faulty MAP sensor or circuit. See MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. Go to step  12 .
  6. Inspect HO2S wiring for open or short circuits. Check for damaged wiring. See appropriate wiring diagram in WIRING DIAGRAMS article. Check HO2S connectors for moisture or corrosion. If no problems are found, go to next step. If any problems are found, repair as necessary and go to step  12 .
  7. Remove Ignition Discharge Module (IDM). Inspect 4 rubber spark plug seals, 4 internal spark plug contact springs and electrical connector for damage, moisture or corrosion. See IGNITION DISCHARGE MODULE (IDM) under MODULES, RELAYS & SOLENOIDS in appropriate SYSTEM & COMPONENT TESTING article. If no problems are found, go to next step. If any problems are found, repair or replace as necessary and go to step  12 .
  8. Remove spark plugs. Inspect electrode for excessive deposits, cracked porcelain or misadjusted spark plug electrode. Spark plug gap should not exceed 0.055" (1.4 mm). Standard plug gap is 0.039" (1.0 mm). If no problems are found, go to next step. If problem is found, replace spark plugs and go to step  12 .
  9. Test IDM coils. See IGNITION DISCHARGE MODULE (IDM) under MODULES, RELAYS & SOLENOIDS in appropriate SYSTEM & COMPONENT TESTING article. If no problems are found, go to next step. If problems are found, repair or replace components as necessary and go to step  12 .
  10. Check engine compression. If more than 29 psi difference exists between any 2 cylinders, repair low compression problem and go to step  12 . If engine compression is as specified, go to next step.
  11. Replace spark plugs. Inspect fuel system operation. See FUEL PRESSURE/FLOW TESTS under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If any problems are found, repair as necessary. Go to next step.
  12. Use scan tool to clear DTCs. Drive vehicle for 5 minutes under varying loads and engine RPM. Recheck for any stored DTCs. If DTC P0300 is present, substitute known good ECM and retest system. See ENGINE CONTROL MODULE (ECM) under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article.
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