EPA/G.M warmup cycle
Runing colder would not trigger errors by itself but if errors were triggered for any reason, EPA mandates to be sure error has been resolved those codes must reside in PCM memory for XX amount of trips the following is G.Ms procedure to comply with OBD-II mandates :
The main intention of the GM OBD-II cycle is to run the OBD-II Main Monitors in order to determine the status of the I/M readiness tests and to have the PCM relearn after a low of power or Keep Alive Memory and errors lost.
The drive cycle can also be used to assist in identifiying any OBD-II concerns that exist by running all of the monitors.
A cold start is a necessary step in preparation to run a complete OBD-II compliant drive cycle.
If a car is driven under the correct coditions, all of the OBD-II monitors will run their various tests, and if a test fails, set a "pending" or hardcode (MIL is llluminated).
Differences in how each monitor runs a test define the type of TRIP needed to run that monitor.
Some monitors are run only on cold engine startup, some only on a highway cruise speed with the TCC off and others at idle speed with A/C off.
Some tests will not run until a car is driven in a drive pattern that meets all of its enable criteria.
Valid Drive cycle table Requirments( total time - 12 minutes)
Cold startup ( coolant temperatre less then 122 degrees)
Idle 2.5 minutes in "D" or "N". A/C & defogger "off"
A/C "off", accelerate to 55 MPH at 1/2 throttle
Steady state Cruise at 55 MPH for 3 minutes
M/T clutch engaged, no braking, Decel to 20 MPH
Accelerate to 55-60 MPH at 3/4 throttle
Steady state Cruise at 55-60 MPH for 5 minutes
Decelerate without braking
End of valid drive cycle.
For PCM to know the position of crank position sensor, PCM must see 5,120 RPMS within drive cycle after power to PCM has been lost.
Note: Specific engine warmup conditions must be met in order to complete all OBD-II tests.
Once an error is triggered under the regulations it must be stored in memory for some timeframe, even when the error has been resolved.
To clear that error, X amount of TRIPS must occur before that error will be erased by the PCM.
OBD-II Warmup cycle
To complete an OBD-II warmup cycle, the engine must reach 160 degrees and achieve a temperature rise of at least 40 degrees from the initial startup engine temperature.
For example a engine could start at 120 and rise to 210 degrees and achieve over a 40 degree change, in this case, the warmup cycle conditions would be met.
However, if a engine started at 150 and rose to 180 degrees, a 40 degree change in engine temps would not have occurred.
In this case, the warmup criteria would not be present and some OBD-II diagnostic tests would not be run.
Thus if you were to install a lower degree thermostat that prevented the 160/200 degree rule, it would take much longer a time period for PCM to relearn and to clear errors stored for XX amount of trips which can be as high a 40 trips.
Keep in mind that there also is a re-learn process that needs to be done for correct idle.
In most cases you would for a MN6 based C5:
Cold start and idle for 5 minutes ( all power functions are off)
Turn on A/C only and continue to idle for aother 5 minutes
Turn A/C off, continue to idle for 5 minutes
Also keep in mind I/M tests which must be in a complete state when you go in for the newer smog tests. If popwer has been lost to PCM or the error codes were erased, the I/M test flags will be set to "not complete" and with a colder engine setup it will take much longer for those tests to get completed.
Without using a PCM scanner you would not know what state the I/M states are and if your state requires I/M testing, you would be rejected in smog testing due to I/M tests never getting to a complete state.