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General Smog Check
 

How To Reset Chevy Silverado 1500 Emission Monitors?

I have a 1999 Chevy Silverado 1500 5.3L. I went in for smog test but it had not completed the emission monitors in the computer. I put another 400 miles on it, and still the same thing. I read the online procedure for a 2001 model. Should I do the same thing to get the monitors to complete? The computer will not go past the secondary air pump test. Thank you.

Answer:  

We understand your Chevy Silverado is having difficulty getting certain emission monitors to complete (become Ready). The emission monitors are programmed to run while your vehicle is being normally operated. However, due to different driving habits, the criteria required to run a monitor may not always be met. Following the Chevy Silverado drive cycle below should allow all emission monitors to complete. The drive cycle must be followed accurately. Take extra caution when performing the drive cycle on public roadways. Perform the drive cycle at your own risk. Perform the drive cycle safely and obey all traffic laws.

Since you mention you've already driven an additional 400 miles after the first smog check inspection where your truck failed the smog test, we're going to recommend that you follow the drive cycle below once, and if after that your truck still has not completed (made ready) all the emission monitors required to pass the smog inspection, seek the assistance of a smog check repair station which will be able to perform the drive cycle on a dynamometer and be utilizing specialized OBD II drive cycle readiness tools/scanner/computer. Mode 6 (emissions diagnostics tool) is especially helpful when trying to complete emission monitors. A well trained smog technician will be able to use Mode 6 to manually run emission monitors.

How to Perform a Chevy Silverado Drive Cycle

The Chevy Silverado drive cycle below will complete or make ready your truck's emission monitors, including the EVAP monitor, Oxygen Sensor monitor, EGR monitor, Secondary Air Injection, and Catalyst monitor. If after completing the drive cycle your Silverado will still not complete any or all the monitor(s) we have to recommend visiting a Chevy dealer or the smog check repair center.

We should note, the secondary air injection monitor which checks for the performance of the air injection system and air injection pump requires the monitor run during a cold (engine) start. Once the engine warms up, the monitor is done checking the air injection pump and will continue on checking the performance of the remainder of the AIR injection system. With that said, it's not the number of miles driven which resets the air injection monitor, rather the number of cold starts required to get all the other parameters required for the air injection monitor to to run. Starting the engine after the vehicle has sat for at least 8 hours in normal weather conditions would be considered a "Cold Start". Since the air injection monitor takes into effect ambient air temperature, it is best to perform a cold start on a morning.

START HERE

A. Cold Start: Begin from Cold Start, and ignition in OFF position for at least 1 hour. Ensure your Chevy Silverado'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. 

B. 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. 

C. Accelerate: Turn off the air conditioner and rear defroster and begin driving your Silverado. 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. 

D. Hold Steady Speed: Hold your speed steady at 55 mph 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. 

E. 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 Silverado 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. 

F. Accelerate: Accelerate again at 3/4 throttle until 55-60 mph is reached. This will perform the same self tests as during the first acceleration step. 

G. Hold Steady Speed: 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. 

H. 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 Silverado at least twice will ensure all monitors run, including the EVAP monitor, and your Chevy Silverado is ready for the smog check.

Should you want to perform specific Monitor self-tests follow the steps below.

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. 

Chevy runs 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

Following the Chevy Silverado drive cycle above should allow all emission monitors to complete. The drive cycle must be followed accurately. Once again, take extra caution when performing the drive cycle on public roadways and perform the drive cycle at your own risk. Drive your truck safely and obey all traffic laws.


posted by SmogTips Support 08-09-2018 04:35 PM
 


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