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Eric, Automotive Repair Shop Manager
Category: Chevy
Satisfied Customers: 32563
Experience:  20+ yrs. experience as repair shop manager and technician.
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I have a 1997 Chevy Astro that wont pass CA smog because several

Resolved Question:

I have a 1997 Chevy Astro that won't pass CA smog because several OBD2 monitors won't clear. They are C, EV, OH. After several trips, the monitors E and O also won't clear. There are no failure codes and the van passes all tailpipe tests. Where do I start?
Submitted: 8 years ago.
Category: Chevy
Expert:  Eric replied 8 years ago.



Below are directions to reset drive cycle and monitors for OBD2 on GM vehicles once fault codes, including pending codes are erased with a scanner. You have to do this exactly as described and in order described:


  • Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup.
    Do not leave the key in 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 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
  • Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) 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 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
  • Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.
  • Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) 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.
  • Customer: replied 8 years ago.
    The van has been through all those cycles many times in the last month. The monitors still don't clear. I've never had this problem before. It came up only at the last smog check at the end of August. I'll clear all the codes, etc and give it another try, but I don't hold out much hope. Do you have any other suggestions?
    Expert:  Eric replied 8 years ago.



    Ok, so you did the exact sequence as described exactly as described. This isnt the same as putting 2000 miles on it. It is a specific condition based sequence of events to achieve the monitor resets.


    I just want to make sure because what you described in your original post says nothing about doing the prescribed monitor reset, only says you put over 2000 miles on it, which in and of itself doesnt reset the monitors

    Customer: replied 8 years ago.
    You're correct. I didn't go through that exact sequence all at once. I'll give it a try and see if it works. The van is cooling off right now and should be ready to run that cycle by now.
    Expert:  Eric replied 8 years ago.



    Ok, what I gave you is straight out of the GM service manual, and I have used many, many times. If done exactly as described it will reset the monitors. If it doesnt, then it needs to be hooked up to a GM scan tool and taken on a monitor reset drive to see where the failure is occurring

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