Random/Multiple Cylinder Misfire Detected


This code indicates that the PCM has detected one or multiple random cylinder misfires in the ignition system.

Code Set Parameters

The PCM uses crankshaft position, camshaft position, and engine RPM to calculate fuel delivery and ignition timing. Variations in camshaft and crankshaft position, as well as engine RPM help the PCM to detect an engine misfire. When an engine misfire is detected that is severe enough to damage the catalytic converter/s, a code will be stored in the PCM and a service engine soon lamp will be illuminated. If the misfire is not considered serious enough to damage the catalytic converter/s, the service engine soon lamp may flash for a period of time (usually under acceleration) and then go off.


These include reduced power, rough idle, choppy acceleration, a stored trouble code, and an illuminated service engine soon lamp.

Common Causes

Common causes of this code are a lean condition caused by insufficient fuel pressure, excessive engine vacuum leak/s, EGR system malfunction, clogged catalytic converter/s. Ignition system component failure is also a possibility when P0300 is stored in the PCM.

Common Misdiagnosis

Ignition system components are often replaced in error when this code is exhibited. It is a possibility but ignition misfires tend to set cylinder specific codes (P0301 through P0312), rather than a random cylinder misfire code.


  • A scanner (or code reader) and a digital volt/ohmmeter will be helpful in successfully diagnosing this code-storing condition. Begin your diagnosis with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • After the codes are cleared, operate the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made. A random cylinder misfire code is easiest to diagnose when obvious symptoms are presented
  • If a P0300 is stored and no symptoms are manifest, then reset the PCM and see if the code returns
  • Is the engine stumbling or hesitating upon acceleration? If so, then make sure that all ignition maintenance tune-up items have been replaced according to the manufacturer’s recommended schedule
  • This includes the spark plugs, spark plug boots (where applicable), ignition coils (or coil packs), distributor cap and rotor button (if equipped), and the fuel filter
  • It is best to replace the spark plugs using OEM replacement parts
  • Resistor spark plugs are cheaper than platinum spark plugs but they are not a viable substitute
  • If no shortcomings are found with the ignition system, then check for a lean exhaust condition by observing the oxygen sensor data
  • Should the data suggests a lean exhaust condition, you would be looking for a major vacuum leak caused by a cracked, broken, or disconnected vacuum hose, an exhaust gas recirculation (EGR) valve malfunction, or clogged catalytic converter/s
  • Unmetered air that enters the engine without entering the MAF can also cause this code to be stored
  • A scanner and access to a factory service manual is critical to a successful diagnosis