MIL On Intermittently, KOER DTC 41 or 42 Set
Bulletin No.022/92
Issued
7/10/92
Revised
Category
F
Applicable Model/s
1991 Navajo
Subject
"CHECK ENGINE" LIGHT ON INTERMITTENTLY
DESCRIPTION
The "Check Engine" light may come on intermittently in some Navajos with automatic transmissions and 0-58A R00/0-58B R00 calibrations. This generally occurs with no other driver symptoms evident, and a self-test error code 41 stored in memory. Key On Engine Running (KOER) error code 41 or 42 may also be present.
INSPECTION & REPAIR PROCEDURE
If the vehicle is found to exhibit the above symptom, the following procedures should be performed. Because several engine problems can set the "Check Engine" light and produce self-test error codes, it is important to follow the procedure below and the procedure in the emissions section of the Workshop Manual to avoid replacement of good parts.
1. Perform the Key On Engine Off (KOEO) and Key On Engine Running (KOER) tests according to the Workshop Manual (Section F-16).
Note:
Record all codes as soon as possible after the customer notices that the "Check Engine" light is on.
2. If code 41 is found to be set in the KOEO test, and/or code 41 or 42 is found to be set in the KOER test, and these are the only codes present, proceed to step 3. If other codes are present, refer to Section F-16 of the Workshop Manual for further instructions.
3. Inspect for air leaks between the Mass Air Flow (MAF) sensor and the upper intake manifold. Check the air hose itself as well as the connections (leaks allow unmetered air to lean out the fuel mixture).
4. If any leaks are found, repair as necessary.
5. Inspect the PCV valve, the vacuum tree, and all the vacuum lines and connections for vacuum leaks, and repair as required.
6. Verify that the fuel pressure is between 30 and 40 PSI with the engine running. Also, check to see that the fuel pressure does not bleed off more than 10 PSI in 1 minute after engine shut down. Refer to Section F-03 of the Workshop Manual if this test fails.
7. Clear all codes (Section F-16, Workshop Manual) and rerun the KOEO and KOER self-tests. Follow the procedures below.
A. If repairs are made and no error codes are present, the service is completed.
B. If no repairs are made and no error codes are present, go to step 9.
C. If error code 41 or 42 is found in the KOER test, proceed to step 8.
8. If the following error codes are set, perform the following service procedures. KOER Code 41:
A. Perform the continuous monitor test (wiggle test) to look for intermittent harness problems (see Workshop Manual, Page F-16-25).
B. Disconnect the Heated Exhaust Gas Oxygen (HEGO) sensor, and check the HEGO heater voltage with the key on.
C. If there is no power at the HEGO heater, check the HEGO heater fuse (10 amp, located in the under-dash fuse box). For exact fuse location, see Workshop Manual, Section T-18.
D. If no problems are found, replace the HEGO sensor.
KOER Code 42:
A. Check the fuel pressure (step 6) and repair any problems found.
B. Disconnect the Heated Exhaust Gas Oxygen (HEGO) sensor and check the HEGO heater voltage with the key on.
C. If there is no power at the HEGO heater, check the HEGO heater fuse (10 amp, located in the under-dash fuse box). For exact fuse location. see Workshop Manual, Section T-18.
D. If no problems are found, replace the HEGO sensor.
9. Perform the continuous monitor test (wiggle test) to look for intermittent harness problems (see Workshop Manual, Page F-16-25).
10. Disconnect the Heated Exhaust Gas Oxygen (HEGO) sensor and the Electronic Engine Control (EEC) module.
11. Check the harness for continuity and possible shorts to ground.
12. Check connectors for pin pushouts and bad terminal crimps.
13. If no wiring problems are found, replace the EEC processor.
PARTS AND WARRANTY INFORMATION