Hello all, I hope someone might be able to help me. I have a 2010 Impala with the V6 3.5 N engine. At a little over 219000 miles the cylinder head deteriorated at cylinder #6, sending engine into hydolock and gallons of antifreeze into exhaust. I replaced the engine( long block, waterpump, plugs, wires, thermostat, o2 sensors, and exhaust from manifolds back), also put a new battery in it because it died. Car sat for aproximatly 5 months waiting for engine, with battery disconnected. I can not get the o2 sensor monitor to reset. I currently have no codes in system, have driven vehicle in all conditions for over 300 miles {and it runs awesome}, and Have many warm ups. Looking for suggestions so that it will pass emissions test in MA. Thanks

Also the car currently has 220000+ miles on it now and still no light or monitor reset.

Do you have a scan tool that can read live data?

Yes I do.

At a steady cruise observe how fast they are switching and what are the upper and lower levels of the swing. Should be swinging from .1 to .9 and switching quickly.
It the sensors are working correctly you may just need to keep doing the drive cycle.

Yes the upstream and downstream sensors are switching between .1 to .9 mv. with the upstream being about .1 mv lower. But both are switching. Thanks for the info.

about how long do you think this might take?

Hmm......Downstream should hang about .7 and not vary nearly like the front.
When the rear is switching like the front it means the cat is not converting and it will set a cat code.
Well. Keep driving it.

Inspection/Maintenance Complete System Set ProcedureDiagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DescriptionThe purpose of the Inspection/Maintenance (I/M) complete system set procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics and complete the trips for those particular diagnostics. When all I/M monitored diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform the Inspection/Maintenance (I/M) Complete System Set Procedure if any I/M System Status indicators are set to NO.
Conditions for Meeting a Cold Start

• The ignition voltage between 10 and 15 V.
• The barometric pressure (BARO) is more than 75 kPa.
• The engine coolant temperature (ECT) at start-up is less than 42°C (108°F).
• The intake air temperature (IAT) is between 2–32°C (36-90°F).
• The engine is OFF for greater than 6 hours or the following conditions must be met:
  • The start-up IAT minus start-up ECT are within 12°C (22°F).
  • The start-up ECT minus start-up IAT are within 50°C (90°F).
• Fuel level is between 25 and 75 %.

Circuit/System VerificationReview the Inspection/Maintenance (I/M) System Status indicators. All I/M System Status indicators should report YES, and no I/M Test DTCs should be present.
Inspection/Maintenance (I/M) System Set ProcedureWarning: Refer to Road Test Warning.

Note: Do NOT touch the accelerator pedal until told to do so. A change in TP Sensor angle or an increase in engine speed may invalidate this portion of the test.

Note: An I/M Test DTC will not be stored or erased from the ECU except at the end of trip processing, which occurs 5 * after ignition OFF.

1. Ensure that the vehicle meets the conditions for a cold start listed above.
   • If the EVAP I/M System Status indicator displays NO, perform the EVAP Service bay test if applicable.
2. Turn OFF all accessories; HVAC system, other electrical loads, including aftermarket/add-on equipment, etc., and open the hood.
3. Set the vehicle parking brake and ensure the vehicle is in park for automatic transmission or neutral for manual transmission.
4. Start and idle the engine for 2 min.
5. Close the hood, release the parking brake and Accelerate at part throttle to 72–80 km/h (45–50 mph) with this speed maintained until the engine reaches operating temperature, 8–10 min .
6. Continue operation under these conditions for an additional 6 min.
7. Accelerate at part throttle to 90 km/h (55 mph) with this speed maintained for 2 min.
8. Release the accelerator pedal for at least 10 *. This will allow the vehicle to enter the decel fuel cut off.
9. Safely stop the vehicle, with the engine in drive for automatic or neutral with the clutch pedal depressed and parking brake applied for manual. Allow the vehicle to idle for 2 min.
10. Shift the vehicle to park for automatic and neutral for manual. Turn OFF the ignition and exit the vehicle. Do NOT disturb the vehicle for 45 min.
11. Observe the Inspection/Maintenance (I/M) System Status with a scan tool. All of the I/M System Status indicators should display YES.
    • If the EVAP I/M System Status indicator displays NO, turn OFF the ignition, ensure that the vehicle meets the conditions for a cold start, and repeat steps 6–11 three more times, or until the EVAP I/M System Status indicator transitions to YES. If the indicator continues to display NO, refer to the Inspection/Maintenance (I/M) System DTC Table to identify the DTCs that did not run.
    • If any of the I/M System Status indicators display NO, refer to the Inspection/Maintenance (I/M) System DTC Table for the indicator which did not display YES. The I/M System DTC Table identifies the DTCs associated with each I/M System Status Indicator.
12. Observe the I/M Test DTC information with a scan tool. Verify there are no I/M Test DTCs present.
    • If an I/M Test DTC is set, diagnose the DTC using the Diagnostic Trouble Code (DTC) List - Vehicle and refer to Inspection/Maintenance System Check.
13. Observe the engine DTC information with a scan tool. Verify no DTCs are present.
    • If a DTC is set, diagnose using the Diagnostic Trouble Code (DTC) List - Vehicle. After repairs, perform the Inspection/Maintenance Complete System Set Procedure to verify no further DTCs are set.
    • You can try performing the drive cycle above. this from si doc #2258640.( I don't believe the links will work for you). Hope this helps.