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Home >> Jeep >> 2021 >> Compass Altitude, FWD >> Repair and Diagnosis >> Engine Performance >> System >> DRIVEABILITY - Non-DTC Based Diagnostics >> Diagnosis And Testing >> Checking The Oxygen Sensor Performance (6 Wire) >> Diagnostic Test

Diagnostic Test

  1. VERIFY O2 SENSOR OPERATION 
    1. Start the engine.
    2. Allow the engine to reach normal operating temperature.
    3. With the scan tool, select and graph the O2 Sensor suspected of not performing correctly.
    4. Review the 3 sample videos of O2 Sensor operation to determine which graph best matches what is displayed on the scan tool for the vehicle.
    5. Which video best matches the graph displayed on the scan tool?
      multimedia:A supplement to the article is available.
      multimedia:A supplement to the article is available.
      multimedia:A supplement to the article is available.

      Video 1 (Normal operation) 

      Video 2 (Rich operation) 

      • Go To  2

      Video 3 (Lean operation) 

      • Go To  3
  2. TESTING FOR RICH O2 SENSOR OPERATION 
    1. Start the engine.
    2. With the scan tool, select and graph the O2 Sensor suspected of not performing correctly.
    3. Disconnect engine vacuum lines to create a lean running condition.
    4. With the engine vacuum lines disconnected monitor the O2 Sensor graph on the scan tool.

      Did the O2 Sensor graph show a change from rich to lean?

      Yes 

      • Check for any of the following conditions/mechanical problems that can cause a O2 Sensor stuck rich condition:
      • AFTERMARKET equipment or software effecting emissions.
      • AIR INDUCTION SYSTEM - must be free from blockage.
      • ENGINE VALVE TIMING - must be within specifications.
      • ENGINE COMPRESSION - must be within specifications.
      • ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
      • ENGINE PCV SYSTEM - must flow freely.
      • FUEL - must be free of contamination.
      • FUEL PRESSURE ABOVE SPEC - faulty regulator.
      • FUEL INJECTOR - plugged, stuck open or restricted injector.

      No 

      • Replace the Oxygen Sensor in accordance with the Service Information.
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  3. TESTING FOR LEAN O2 SENSOR OPERATION 
    1. Start the engine.
    2. With the scan tool, select and graph the O2 Sensor suspected of not performing correctly.
    3. Create a rich running condition.
    4. With the rich running condition, monitor the O2 Sensor graph on the scan tool.

      Did the O2 Sensor graph show a change from lean to rich?

      Yes 

      • Check for any of the following conditions/mechanical problems that can cause a O2 Sensor stuck lean condition:
      • AFTERMARKET equipment or software effecting emissions.
      • AIR INDUCTION SYSTEM - must be free from leaks.
      • ENGINE VACUUM LEAK- must be at least 13 inches in neutral.
      • ENGINE VALVE TIMING - must be within specifications.
      • ENGINE COMPRESSION - must be within specifications.
      • ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
      • ENGINE PCV SYSTEM - must be free of leaks and flow freely.
      • POWER BRAKE BOOSTER - no internal vacuum leaks.
      • FUEL - must be free of contamination.
      • FUEL PRESSURE BELOW SPEC - restriction in system or faulty pump.
      • FUEL INJECTOR - plugged or restricted injector.

      No 

      • Replace the Oxygen Sensor in accordance with the Service Information.
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
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