DTC P0301-P0304: Cylinder Misfire Detected

If misfiring is frequent enough to trigger detection of increased emission during 2 consecutive driving cycles, Malfunction Indicator Light (MIL) will illuminate, and DTC P0300 and some combination of P0301-P0304 will be stored in memory. If misfiring is frequent enough to damage catalyst, MIL will blink whenever misfiring occurs, and DTC P0300 and some combination of P0301-P0304 will be stored in memory. When misfiring stops, MIL will still remain on.

1. If DTCs P0301, P0302, P0303, and/or P0304 is set, check for:
   • A fuel injector that is clogged, leaking fuel or air.
   • An open or shorted fuel injector circuit.
   • A spark plug carbon deposits, fouling or other malfunction.
   • Ignition wires open or shorting.
   • A distributor malfunction.
   • Low engine compression.
   • Valve adjustment out of specification. See ON-VEHICLE ADJUSTMENTS article.

   Repair as necessary. If no problems are found, go to next step.

2. Start engine and listen for clicking sound at fuel injector in suspect cylinder. If injector clicks, go to next step. If injector does not click, check for open or short in wiring harness between fuel injector and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, replace fuel injector and recheck. If misfire is still detected, substitute a known-good PCM and recheck. See SUBSTITUTING PCM in SELF-DIAGNOSTICS - INTRODUCTION article. If symptom or indication goes away, replace original PCM.
3. Check and record freeze frame data. Perform PCM reset procedure. See SELF-DIAGNOSTICS - INTRODUCTION article. If there is no freeze frame data of misfiring, clear DTCs. With or without freeze frame data, exchange spark plug from misfiring cylinder with one from another cylinder. Connect SCS Service Connector (07PAZ-0010100). Test drive vehicle several times in the range of freeze frame data or under various conditions to try to duplicate malfunction if freeze frame data is not available.
4. Using scan tool, check for DTCs. If any DTC is indicated, go to next step. If DTCs are not indicated, misfire condition is intermittent due to spark plug fouling, etc. Plugs are firing properly at this time.
5. If misfiring occurs in other cylinder whose spark plug was exchanged, replace spark plugs. If misfiring does not occur in other cylinder whose spark plug was exchanged, exchange fuel injector from misfiring cylinder with one from another cylinder. Start engine and allow it to idle for 2 minutes.
6. Test drive vehicle several times in the range of freeze frame data. If there is no freeze frame data of misfiring, test drive vehicle under various conditions to try to duplicate malfunction.
7. If DTC P0301, P0302, P0303, or P0304 is indicated, go to next step. If DTCs are not indicated, misfire condition is intermittent due to bad contact in fuel injector connector. Injectors are operating properly at this time.
8. If misfiring occurs in other cylinder whose fuel injector was exchanged, replace faulty fuel injector. If misfire does not occur in the other cylinder whose fuel injector was exchanged, check valve clearance, cylinder leak down, engine compression and Crankshaft Speed Fluctuation (CKF) sensor. Repair as necessary.