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How to get catalytic converter monitor ready

Perform the specified drive cycle to get a catalytic converter monitor ready

The catalytic converter monitor is a test that evaluates the ability of the converter to reduce harmful emissions. The catalytic converter’s job is to use left over oxygen from combustion to burn off any left over fuel in the exhaust. In a perfect world, all the oxygen would be used up during the combustion process. But there’s no such thing as a perfect air/fuel mixture and perfect combustion. There’s always some amount of left over oxygen or left over fuel after combustion.

The emissions system places an oxygen sensor upstream from the catalytic converter and another oxygen sensor after the converter. The PCM measures how much oxygen enters the converter versus how much exits the converter. If the oxygen value is the same on both sensors, the converter isn’t doing its job. To double check, the PCM forces rapid pulses of extra air and fuel into the engine and then checks for sensors to see how well the converter handles the extra fuel and air.

This testing routine is referred to as a heated catalyst monitor and it must pass the test in order for the readiness monitor to be set to the ready state.

The computer runs the monitor during a drive cycle

A drive cycle is a pattern of driving that puts the catalytic converter through multiple driving scenarios to make sure it works properly in each scenario. Each carmaker has their own specific drive cycle. Most catalytic converter monitors are “two-trip” tests. In other words, the monitor must see two drive cycle failures before it will turn on the check engine light.

You must meet the catalytic converter monitor’s enabling criteria before the test will run

As mentioned above, each carmaker develops their own drive cycle to complete the converter monitor testing. Each has some prerequisites (enabling criteria) that must be met before the test will even start. Here’s an example:

Catalytic converter monitor enabling criteria examples

• The PCM must complete an oxygen sensor monitor drive cycle prior to running the catalytic converter monitor and it must pass the oxygen sensor monitor first
• The check engine light must be off with no trouble codes pending
• Fuel tank must be 35% to 85% full.
• The engine must be either cold (not driven for at least 8 hours
• Coolant must be above a minimum temperature
• The engine must have been running, or not running for a certain number of minutes.
• The catalytic converter monitor will only start after it see the vehicle cruising at 55 mph for 5 minutes

Then do a catalytic converter drive cycle

Most catalytic converter drive cycle procedures require a cold start

• Idle the cold engine for at least 2 minutes with rear defroster and AC ON
• Drive the vehicle at a steady speed of 55 MPH
• Turn off  the rear defroster and ac and keep the speed of your vehicle at 90 km/hr (55MPH) nearly for 3 minutes. During this period, the purge and Fuel monitor diagnostics will take place.
• Decelerate your vehicle’s speed at 20 MPH
• Gradually decrease speed to 32 km/hr (20 MPH). Avoid touching/shifting of clutch or brake.
• Speed up again.
• Drive your vehicle back to 55MPH (90 km/hr) at 3/4 throttle for nearly five minutes.
• Stop the vehicle
• Idle for 2 minutes.

Once you know the enabling criteria are met and you have the drive cycle procedure, do the drive cycle. If the converter is performing up to specification, your scan tool will show the catalytic converter monitor ready. Then you can take it in for emissions testing.

©, 2022 Rick Muscoplat

Posted on by Rick Muscoplat



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