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2003 Chevy S10 4.3L Having Trouble Setting EVAP Monitor

My Chevy S-10 had a small leak in the EGR hose. I fixed it and reset the service engine soon (SES) light using a scan tool. Well all the emission monitors erased as well, and now I'm having trouble getting the EVAP monitor to complete. The rest of monitors are fine. I need the drive cycle. I have already tried the cold start with the a/c on and engine idling for 2 minutes, then accelerate 1/4 throttle and so on, but it hasn't worked. Maybe there is a manufacturer specific drive cycle? Need help. Thanks.


The driving pattern to complete the EVAP monitor is below. We do recommend however that you complete an entire drive cycle just to ensure the required parameters are met in order to begin the EVAP portion of the driving cycle. Setting the EVAP monitor is one of the more difficult and time consuming monitors to complete. If all is well (engine emission wise) it will set with time and proper driving pattern.

Chevy S-10 Drive Cycle (EVAP Monitor ONLY)

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.

NOTE: The ECU will run the EVAP Monitor once the engine has been shut down and ignition turned off.

Complete Chevy S-10 Drive Cycle (Set All Monitors)

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. Ensure 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.

ACCELERATE: 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).

posted by SmogTips Support

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