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Test NTC-10A: Checking Oxygen Sensor Switching

WARNING: High fuel pressure may be present in fuel lines. Open fuel system with caution. See FUEL PRESSURE RELEASE .
NOTE: 1/2 and 1/3 Heated Oxygen Sensor (HO2S) switching should be slower than 1/1 or 2/1 HO2S switching.
NOTE: 1/1 HO2S is located in upstream position. On models with 2 upstream HO2S, 1/1 HO2S is located in left upstream position. On AN body (2WD) with 5.9L engine and BE/BR bodies with 8.0L medium-duty engine, 1/2 Heated Oxygen Sensor (HO2S) is located in pre-catalyst position. On all other bodies, 1/2 HO2S is located in downstream position. On models equipped with 4 HO2S, 1/2 HO2S is located in left downstream position. 1/3 HO2S is used on BE/BR bodies with 8.0L medium-duty engine only and is located in post-catalyst position. 2/1 HO2S is located in right upstream position on models with 2 upstream HO2S.
  1. Allow engine to reach normal operating temperature. Using scan tool, read HO2S voltages. If HO2S states are switching between RICH and LEAN, system is functioning properly. Test is complete. If either HO2S is locked on LEAN, perform TEST NTC-10B: CHECKING OXYGEN SENSOR SWITCHING . If neither HO2S is locked on LEAN, go to next step.
  2. Turn engine off. Release fuel pressure. Connect fuel pressure gauge to fuel rail. Turn ignition on. Using scan tool, actuate fuel system test. Allow fuel pressure gauge to stabilize to normal fuel pressure. Stop fuel system actuation test. Go to next step.
  3. Monitor fuel pressure gauge for one minute. If fuel pressure gauge reading drops more than 10 psi (0.7 kg/cm2 ), replace leaking injector(s) as necessary and perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES  on AB body, or TEST VER-2A: ROAD TEST VERIFICATION  on all other bodies. If fuel pressure gauge reading does not drop more than 10 psi (0.7 kg/cm2 ), go to next step.
  4. Inspect air cleaner and inlet ducts for restrictions. Repair air cleaner and inlet ducts as necessary and perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES  on AB body, or TEST VER-2A: ROAD TEST VERIFICATION  on all other bodies. If no restrictions exist, perform TEST NTC-13A: CHECKING ENGINE MECHANICAL SYSTEMS (GASOLINE ENGINES) .
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