[JamesKilcarr]

Originally Posted by Mike Benvo

Many people have asked me:
1) How long will it take for the light to come on?
2) Why do some cars trigger the light sooner than others?
3) Will my driving style affect how long it takes to trigger the light?

Here are the answers of how setting readiness works. The CEL is thrown after readiness FAILS and may require MULTIPLE drive cycles to ensure that all testing conditions are met:

An example of a drive cycle is as follows:
1. Engine cold start, idling, approximately 3 minutes.

Evaluated:

• Secondary Air System
• Evaporative Leak Detection (LDP Equipped Vehicles)

2. Constant driving at 20 to 30 MPH, approximately 4 minutes.

Evaluated:

• Oxygen Sensors - Achieved “Closed Loop” Operation
• Oxygen Sensors - Response Time and Switching Time (Control Frequency)

3. Constant driving at 40 to 60 MPH, approximately 15 minutes (sufficient vehicle coasting phases included).

Evaluated:

• Catalytic Converter Efficiency
• Oxygen Sensors - Response Time and Switching Time (Control Frequency)

4. Engine idling, approximately 5 minutes.

Evaluated:
Tank-Leak Diagnosis (DMTL Equipped Vehicles after KL 15 is switched OFF) US Spec M3's are DMTL Equipped and KL15 means ignition on.

Now the reason of why some cars take MUCH longer than others to throw the error light - Driving Style!

The diagnostic sequence illustrated above will be interrupted if:
• The engine speed exceeds 3000 RPM.
• Large fluctuations in the accelerator pedal position.
• The driving speed exceeds 60 MPH.

The Service Engine Soon / Increased Emissions! warning will be illuminated under the following conditions:
• Upon the completion of the next consecutive driving cycle where the previously faulted system is monitored again and the emissions relevant
fault is again present.

• Immediately if a “Catalyst Damaging” fault occurs (Misfire Detection).

The illumination of the light is performed in accordance with the Federal Test Procedure (FTP) which requires the lamp to be illuminated when:

• A malfunction of a component that can affect the emission performance of the vehicle occurs and causes emissions to exceed 1.5 times the standards required by the (FTP).
• Manufacturer-defined specifications are exceeded.
• An implausible input signal is generated.
• Catalyst deterioration causes HC-emissions to exceed a limit equivalent to 1.5 times the standard (FTP).
• Misfire faults occur.
• A leak is detected in the evaporative system, or “purging” is defective.
• ECM fails to enter closed-loop oxygen sensor control operation within a specified time interval.
• Engine control or automatic transmission control enters a "limp home" operating mode.
• Ignition is on (KL15) position before cranking = Bulb Check Function.

There you have it. Everything you need to know about readiness testing, how it's tested, and why some cars take longer than others to record an error.

okay thank you so much!