How to Reset an Engine Computer Monitor Program

A computer monitor is a program or series of programs inside the car's main engine control computer that will run individual tests and performance checks of specific systems such as the catalytic converter or EVAP systems. When these monitors are in transit, or test mode without completion the monitor is not "set" or satisfied therefore not ready, this condition will not allow the car to have an emission test.

How to Set Monitors

Each monitor program will vary from one manufacturer to the next so there is no set way to close a monitor, but as a general rule of thumb this is how it is done:

  • Start the engine and allow it to warm up to its operating temperature.
  • Drive the car about 10 to 15 miles and shut the car off and allow it to fully cool, preferably overnight. This should be done at least two or three times.
  • Once the drive cycles are completed the monitors will reset or trigger a check engine light with a pending code.

Some scanners or code readers can tell you if the monitors have been reset which is called a "monitor readiness status". This feature can help you know exactly when the monitors are ready and the car can be emissions tested.

Monitor Doesn't Set?

Occasionally a monitor will not reset, this is because the computer could have a P1000 code which means there is something disabling the monitor's function. A popular cause for this is a bad thermostat which is stuck open, this will exceed the engine warm up time which will shut the monitoring off until repaired. Anytime there is a trouble code the monitors will not run.


Our certified technicians are ready to answer PCM monitor questions for free. We hope you saved money and learned from this guide. We are creating a full set of car repair guides. Please subscribe to our 2CarPros YouTube channel and check back often for new videos which are uploaded regularly.

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