Diagnostic Procedure

DTC 25 Air-Fuel Ratio Lean Malfunction

DIAGNOSTIC PROCEDURE
1. Check voltage of terminal VF of the data link connector (DLC1).
- Failure type 1, go to step 2.
- Failure type 2, go to step 7.

2. Check voltage of terminal OX1 of the data link connector (DLC1).
- If OK proceed to step 7.
- If not OK go to step 3.

3. Check for open and short in harness and connector.
- 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.
- If OK proceed to step 5.
- If not OK repair or replace items as necessary.

5. Check compression.
- If OK proceed to step 6.
- If not OK repair engine as necessary.

6. Does malfunction disappear when a good main[1] oxygen sensor is installed?
- If Yes, replace main[1] oxygen sensor.
- If No, Check and replace engine control module (ECM).

7. Check each item found to be a possible cause of problem.
- If OK proceed to step 8.
- If not OK

8. Check compression.
- If OK proceed to step
- If not OK repair engine as necessary.

9. Does malfunction disappear when a good main[1] oxygen sensor is installed?
- If Yes, replace main[1] oxygen sensor.
- If NO check and replace ECM.
[1] "Main" oxygen sensor reference is for Ca. spec. vehicles only. All others have only 1 oxygen sensor.