Erasing or clearing the check engine light is in essence resetting the engine control computer (ECU). This not only turns off the check engine light (in most cases very temporarily) but more importantly erases any trouble codes and all the emission monitors. The "monitors" are internal tests which the ECU performs to check itself and specific systems related to engine emissions, i.e. the EGR system, the EVAP system, Catalyst, so on. In this specific case it appears all your Cavalier's monitors were erased due to the reset. You will need to complete a Chevy Cavalier Drive Cycle in order to set the emission monitors (make the monitors Complete).
Note: Performing the drive cycle will only set the required monitors if there aren't any emission related problems your Cavalier's engine is experiencing. We mention this because, if after at least 2 attempts, the drive cycle does not allow all emission monitors to complete, your Chevy might have an emissions problem which will need repair first. Having had the vehicle's check engine light on is a strong indication that this might be the case.
Usually driving in both city and highway conditions over the course of a few days is enough to get the drive cycle to run and set the monitors. At times however, due to individual driving habits, following the recommend drive cycle is required.
Follow the drive cycle carefully. Take extra caution when performing the drive cycle on public roadways. If you feel you will be unable to follow the drive cycle safely, please seek assistance from an smog check repair station or Chevy service center. They may be able to perform the drive cycle utilizing a dynamometer, and specialized scan tools. Perform the drive cycle at your own risk.
Chevy Cavalier Drive Cycle
The following is a General Motors Drive Cycle Pattern which should allow your vehicle to complete all its emission monitors. Be sure to obey all traffic laws while performing drive cycles. Perform acceleration steps only on highways)
Cold Start: Begin from Cold Start, and ignition in OFF position for at least 1 hour. Insure 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 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.
Start Drive: Turn off the air conditioner and rear defroster and begin driving. 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: Now 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 you want to slowly let off the accelerator pedal. Do not brake or shift in order to slow down (don't press the clutch if equipped). It is important to let the 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).
