Test NTC-10A: Checking Oxygen Sensor Switching

NOTE: Perform TEST NTC-1A: NO TROUBLE CODES (NTC) TESTS before proceeding.

WARNING: High fuel pressure may be present in fuel lines. Open fuel system with caution. See FUEL SYSTEM PRESSURE RELEASE procedure in SELF-DIAGNOSTICS section in this article.

NOTE: During first step, observe downstream O2S voltage should switch slower than upstream O2S voltage.

For O2 sensor identification see O2 SENSOR IDENTIFICATION table. Start engine. Allow engine to reach normal operating temperature of 180°F (82°C). Using scan tool, read O2S signal voltages. If O2S signal voltages are switching normally, O2 sensors are functioning normally. Test is complete. If O2S signal voltages are not switching normally, go to next step.

O2 SENSOR IDENTIFICATION

Application	Location
O2S 1/1	Right Bank Upstream O2S
O2S 1/2	Right Bank Downstream O2S
O2S 2/1	Left Bank Upstream O2S
O2S 2/2	Left Bank Downstream O2S

If any O2S state is locked on LEAN, go to TEST NTC-10B: CHECKING OXYGEN SENSOR SWITCHING . If any O2S state is not locked on LEAN, turn ignition off. Release fuel pressure. Install a fuel pressure gauge to fuel rail. Turn ignition on. Using scan tool, actuate ASD fuel system test. Allow fuel pressure gauge to stabilize for one minute. Go to next step.
Using scan tool, stop ASD fuel system actuation. Observe fuel pressure gauge for one minute. If fuel pressure is less than 10 psi (0.7 kg/cm² ), replace leaking injector(s) as necessary if fuel pump and fuel lines are okay. Perform TEST VER-2A: ROAD TEST VERIFICATION . If fuel pressure is 10 psi (0.7 kg/cm² ) or more, go to next step.
Inspect air filter and inlet ducts for restrictions. If restrictions are present, clean inlet system as necessary. Perform TEST VER-2A: ROAD TEST VERIFICATION . If restrictions are not present, go to TEST NTC-13A: CHECKING ENGINE MECHANICAL SYSTEMS .