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
Detail :
A complete driving cycle should perform diagnostics on all systems. A complete driving cycle can be done in under fifteen minutes.
To perform an OBDII Driving cycle do the following:
Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.
Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.
End of valid drive cycle.
Note: Specific engine warmup conditions
must be met in order to complete all OBD-II tests.
Engine running, ECT input increases 40 degrees AFTER engine startup has reached 160 degrees.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
