First, let's make sure the check engine light is not on. If it's on... that'll have to be fixed first. More than likly the fault causing the light to turn on is also stopping the EVAP monitor from setting. If the CEL is not on, we'd question whether you've driven your Chevy Blazer enough to get it to run all the monitors on its own. It usually takes 200-300 miles and over the course of a few days to get the monitors to run; unless you drive it through the drive cycle we show below. A drive cycle should complete on its own while driving routinely. At times though and due to our individual driving habits and patterns we might sometimes not hit the right parameter to run a particular monitor. In such cases we perform a drive cycle.
A few specifics about the EVAP monitor. It will not run unless your Blazer is in closed loop... meaning the oxygen sensor has relayed a good signal to the computer after the engine has warmed up for about 3 minutes. The monitor will also check the system after you've stopped your vehicle and shut it down. The EVAP monitor will also not run unless your Blazer has 1/4 to 3/4 fuel in the tank.
How to Perform a Chevy Blazer OBD-II Drive Cycle (All Monitors)
The drive cycle below will "complete" or make "ready" your vehicle's emission monitors, including the EVAP monitor, Oxygen Sensor monitor, and EGR monitor.
Be sure to obey all traffic laws while performing drive cycles. Perform the drive cycle at your own risk.
Start Here:
COLD START: Begin from Cold Start, and ignition in OFF position for at least 1 hour. Insure your Chevy Blazer's fuel tank is between 1/4 and 3/4 full. Engine coolant temperature must be below 122°F and within 11°F of the ambient air temperature. Do not leave the key on prior to the cold start or the heated oxygen sensor (O2) diagnostic may not run.
IDLE TIME: Run engine (do not drive) for 2 1/2 minutes with the air conditioner on and rear defroster on. During this period the ECU will be running the Oxygen Sensor Heater self-test, Air Injection System Passive Air test, EVAP Purge "No Flow" test, Misfire Detection.
ACCELERATE: Turn off the air conditioner and rear defroster and begin driving your Chevy Blazer. As soon as possible apply half throttle until 55mph is reached. The ECU will now run self-tests on the Misfire Detection, Fuel Trim, and EVAP Purge Flow.
HOLD STEADY: Hold your speed steady at 55mph for three minutes. During this time the Oxygen Sensor O2 response, Air Intrusive (AIS System), EGR Flow, Purge Valve, Misfire Detection, and Fuel Trim diagnostics will be performed.
DECELERATE: During this step slowly let off the accelerator pedal. Do not brake or shift in order to slow down. It is important to let your Blazer vehicle coast along gradually slowing down to 20 mph. The ECU will once again self-test the EGR System, EVAP Purge System and Long Term Fuel Trims.
ACCELERATE: Go ahead and accelerate again at 3/4 throttle until 55-60mph is reached. This will perform the same self tests as during the first acceleration step.
HOLD STEADY: Hold steady speed once again. This time at 55mph for five minutes. During this time, in addition to running the self-tests as during the first HOLD STEADY step, the ECU will perform the catalyst monitor diagnostics. If the catalyst (Catalytic Converter) is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst,or in order to Complete the CAT Monitor.
DECELERATE: This will perform the same diagnostics as in the first Deceleration. Remember not to press the brakes or shift gears (don't press the clutch if equipped).
This ends the drive cycle. Performing the drive cycle on your Chevy Blazer at least twice will ensure all monitors run, including the EVAP monitor, and your Chevy Blazer is ready for the smog check. This is assuming emission systems malfunctions do not exist.
Setting Individual Chevy Blazer Monitors
Catalyst Monitor (CAT):
Prerequisite: No trouble codes present, Intake Air Temperature (IAT) above 32 Degrees (F), Engine Coolant Temperature (ECT) is above 167 Degrees (F); Mass Air Flow sensor is indicating greater than 15 gm/s, engine load is below 63% and steady, engine speed is below 3000 RPM.
1. Idle vehicle 5 minutes (achieve closed loop)
2. Drive 5 min at steady speed above 55 mph
3. Drive 2 min at steady 40 mph
4. Drive 2 min at steady 55 mph
EGR Monitor (EGR):
Prerequisite: No trouble codes present, Engine Coolant Temperature (ECT) is above 75 Degrees (F); barometric pressure (BARO) above 72kPa.
1. Idle vehicle 5 minutes (achieve closed loop)
2. Accelerate and drive for 1 min at steady speed above 50 mph
3. Slow vehicle down to 20 mph. Do not use brake clutch, or shift gears.
4. Repeat steps two and three 5 times.
GM and Chevy run their EGR monitor during the deceleration portion of the drive cycle.
Evaporative Monitor (EVAP):
Prerequisite: No trouble codes present, Fuel tank between 1/4 and 3/4 full.
1. Drive 5 min at steady speed between 30 and 60 mph
2. Stop vehicle and idle engine for 4 minutes.
3. Turn engine off. Remove ignition key.
The ECU will run the EVAP Monitor once the engine has been shut down and ignition turned off.
O2 Sensor Monitor (O2):
Prerequisite: No trouble codes present, Intake Air Temperature (IAT) above 32 Degrees (F); Engine Control Temperature (ECT) is above 167 Degrees (F)
1. Idle vehicle 4 minutes (achieve closed loop)
2. Drive 3 min at steady speed above 50 mph
3. Drive 2 min at steady 40 mph
4. Drive 2 min at steady 50 mph
