Inspection Procedure

DTC 25 Air-Fuel Ratio Lean Malfunction

PROCEDURE
1. CHECK VOLTAGE BETWEEN TERMINALS VF1 AND E1 OF DATA LINK CONNECTOR 1 (DLC 1).
- Warm up engine at normal operating temperature.



- Connect terminals TE1 and E1 of DLC 1.
- Connect positive probe to terminal VF1 and negative probe to terminal E1 of DLC 1.
- Warm up the oxygen sensor by running engine at 2,500 rpm for about 2 minutes.
- Then, maintaining engine at 2,500 rpm, count how many times needle of voltmeter fluctuates between 0.0 volts and 5.0 volts.

Needle should fluctuate 8 times or more: OK

- If not OK (voltage steady at 0.0 volts) proceed to step 2.
- If not OK (voltage steady at 5.0 volts) proceed to step 7.

2. CHECK VOLTAGE BETWEEN TERMINALS OX1 AND E1 OF DLC 1.
- Warm up engine at normal operating temperature.



- Measure voltage between terminals OX1 and E1 of DLC 1 when engine is suddenly raced to full throttle.
- The voltage should be 0.5 volts or higher at least once.
- If OK proceed to step 7.
- If not OK proceed to step 3.

3. CHECK FOR OPEN AND SHORT IN HARNESS AND CONNECTOR BETWEEN ECM AND MAIN OXYGEN SENSOR, ECM AND DLC 1.
- If OK proceed to step 4.
- If not OK repair or replace harness or connector.

4. CHECK EACH ITEM FOUND TO BE A POSSIBLE CAUSE OF PROBLEM IN THE ORDER GIVEN.

- Main oxygen sensor signal continues at 0.0 volts:
1. Faulty sensor installation.
2. Air leakage.
3. Misfire.
4. Fuel system.
5. Injector circuit.
6. Characteristic deviation in engine coolant temperature sensor.
7. Characteristic deviation in intake air temperature sensor.
8. Characteristic deviation in manifold absolute pressure sensor.
9. Valve timing.

- If OK proceed to step 5.
- If not OK repair or replace.

5. CHECK COMPRESSION.
- If OK proceed to step 6.
- If not OK repair or replace.

6. DOES MALFUNCTION DISAPPEAR WHEN A GOOD MAIN OXYGEN SENSOR IS INSTALLED?
- If not OK proceed to step 7.
- If OK replace main oxygen sensor.

7. CHECK EACH ITEM FOUND TO BE A POSSIBLE CAUSE OF PROBLEM IN THE ORDER GIVEN.

- Main oxygen sensor signal continues at 5.0 volts:
- Fuel system.
- Injector circuit.
- Characteristic deviation in engine coolant temperature sensor.
- Characteristic deviation in intake air temperature sensor.
- Characteristic deviation in manifold absolute pressure sensor.
- Valve timing.

- Main oxygen sensor signal is normal:
- Air leakage.
- Fuel system.
- Misfire.
- Valve timing.
- Characteristic deviation in engine coolant temperature sensor.
- Characteristic deviation in intake air temperature sensor.
- Injector circuit.
- Characteristic deviation in manifold absolute pressure sensor.

- If OK proceed to step 8.
- If not OK repair or replace.

8. CHECK COMPRESSION.
- If OK proceed to step 9.
- If not OK repair or replace.

9. DOES MALFUNCTION DISAPPEAR WHEN A GOOD MAIN OXYGEN SENSOR IS INSTALLED?
- If YES replace main oxygen sensor.
- If NO check and replace ECM.