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Test NTC-7: Checking For O2S Switching

NOTE: Possible causes are: O2S voltage less than .10 volts, O2S signal circuit short to ground, air filter or duct restrictions, fuel pump, fuel lines or injectors defective or engine vacuum problem.
  1. Start engine and warm engine to normal operating temperature. With engine running, use scan tool to read oxygen sensor voltage for each oxygen sensor for at least 10 seconds. Downstream oxygen sensor voltage should switch slower than the upstream oxygen sensor voltage. If oxygen sensor voltage for each oxygen sensor is switching normally, test is complete. If oxygen sensor voltage for each oxygen sensor is not switching normally, go to next step.
  2. If upstream oxygen sensor remains locked on lean, go to next step. If upstream oxygen sensor does not remain locked on lean, go to step  9 .
  3. Turn ignition on with engine off. Using scan tool, read oxygen sensor voltage for each oxygen sensor. If oxygen sensor voltage is less than .1 volt for upstream or downstream oxygen sensor, go to next step. If oxygen sensor voltage is .1 volt or more for upstream or downstream oxygen sensor, go to step  7 .
  4. Start engine and allow engine to idle. Check engine vacuum for abnormal vacuum reading. If vacuum is normal, go to next step. If abnormal vacuum reading exists, repair as necessary. Perform TEST VER-2A: ROAD TEST FOR NON-OBD II  .
  5. Turn ignition off. Disconnect connector for the appropriate oxygen sensor in which the oxygen sensor voltage was less than .1 volt. Disconnect Powertrain Control Module PCM connector C1 (located nearest to front of vehicle) and PCM connector C2 (located nearest to rear of vehicle). PCM is located to left of Power Distribution Center (PDC) in engine compartment. Inspect electrical connector and clean/repair as necessary. Using a DVOM, check resistance of O2S signal circuit between PCM connector C1 terminal No. 30 (Black/Dark Green wire) and chassis ground (for upstream O2S), or between PCM connector C2 terminal No. 51 (Tan/White wire) and chassis ground (for downstream O2S). If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair O2S signal circuit short to ground. Perform TEST VER-2A: ROAD TEST FOR NON-OBD II  .
  6. If no other potential causes are remaining, O2S that was less than .10 volts is assumed to be defective. Replace affected O2S. Perform TEST VER-2A: ROAD TEST FOR NON-OBD II  .
  7. Start engine and idle. Check engine vacuum for abnormal vacuum reading. If vacuum is normal, go to next step. If abnormal vacuum reading exists, repair as necessary. Perform TEST VER-2A: ROAD TEST FOR NON-OBD II  .
  8. With engine idling and at normal operating temperature, use scan tool to reset adaptive fuel memory. Using scan tool, read oxygen sensor voltage for each oxygen sensor for at least 10 seconds. The downstream oxygen sensor voltage should switch slower than the upstream oxygen sensor voltage. If oxygen sensor voltage for each oxygen sensor is switching normally, oxygen sensors are operating properly and test is complete. If oxygen sensor voltage for each oxygen sensor is not switching properly, perform TEST NTC-4: CHECKING ENGINE MECHANICAL SYSTEMS  .
  9. Check fuel pressure. Turn ignition off. Release fuel pressure. Remove fuel pump relay from Power Distribution Center (PDC). Start engine and run until engine stalls (removing fuel pump relay will set a DTC). On 2.0L/2.4L engines, connect Fuel Pressure Gauge (C-4799-B) to fuel rail. On 2.5L engine, use Adapter (6539) between fuel rail and chassis supply line, then connect Fuel Pressure Gauge (C-4799-B) to adapter. On all vehicles, reinstall fuel pump relay. Turn ignition on. Using scan tool, actuate ASD fuel system test. Allow fuel pressure to stabilize. Using scan tool, stop ASD fuel system test. Observe fuel pressure gauge for one minute. If fuel pressure is 10 psi or more, go to next step. If fuel pressure is less than 10 psi, replace leaking fuel injectors as necessary. Perform TEST VER-2A: ROAD TEST FOR NON-OBD II  .
  10. Inspect air cleaner and inlet ducts for restrictions. If no restrictions exist, perform TEST NTC-4: CHECKING ENGINE MECHANICAL SYSTEMS  . If air cleaner or inlet ducts are restricted, repair as necessary. Perform TEST VER-2A: ROAD TEST FOR NON-OBD II  .
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