MIL Intermittently ON/Error Codes 41 or 42 Set
9214ford01
Article No.
92-6-15
March 11, 1992
WARNING LIGHT - CHECK ENGINE - INTERMITTENTLY LIT WITH NO DRIVE SYMPTOMS EVIDENT - VEHICLES WITH 4.0L ENGINE AND AUTOMATIC TRANSMISSION
LIGHT TRUCK: 1991 EXPLORER
CALIBRATION: 0-58A-R00, 0-58B-R00
WARNING: THIS MODIFICATION IS AUTHORIZED ONLY FOR THE LISTED ENGINE. PERFORMING THIS MODIFICATION ON OTHER ENGINE CALIBRATIONS IS UNAUTHORIZED AND COULD CREATE LIABILITY UNDER APPLICABLE FEDERAL OR LOCAL LAWS.
This TSB article is being republished in its entirety to delete the reference to 1992 vehicles and to change the condition code.
ISSUE: The "Check Engine" Light may come on intermittently when generally there is no other drive symptom evident and a Self-Test error code "41" is stored in memory. Key On Engine Running Self-Test (KOER) error codes "41 or 42" may also be present. Since several engine concerns can set the "Check Engine" light and produce Self-Test error codes, it is important to carefully follow the diagnostics listed below and in the 1991 Engine/Emissions Diagnosis Manual to avoid replacing good parts.
ACTION: If service is required, use the following service procedure to help identify and correct intermittent "Check Engine" Light complaints.
1. Perform KOEO and KOER Self-Test as soon as possible after the customer notices that the "Check Engine" Light is on and record all codes.
^ If a code "41" in KOEO (continuous memory) test and/or code "41 or 42" in KOER Test are the only codes found, proceed with Step 2.
^ If other codes are present refer to the 1991 Powertrain Control/Emissions Diagnosis Manual for direction.
2. Inspect for air leaks between the mass air flow 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). Repair as required.
3. Inspect the PCV valve, the vacuum tree, and all the vacuum lines and connections for vacuum leaks. Repair as required.
4. Confirm that the fuel pressure is between 30 and 40 PSI with the engine running.
a. Check to see that the fuel pressure does not bleed off more than 10 PSI in one (1) minute after engine shutdown.
b. If this test fails, refer to the Powertrain Control/Emissions Diagnosis Manual, Fuel Delivery Systems Section, for system diagnosis.
5. Clear all codes and rerun the KOEO and KOER Self-Tests.
a. If repairs were made and NO error codes are present, service is complete.
b. If NO repairs were made, and there are NO error codes present, go to Step 8.
c. If error code "41 or 42" is found in KOER Self-Test, proceed with Steps 6 or 7.
6. Perform the following tests for code "41" KOER.
a. Perform the wiggle test to look for intermittent harness concerns.
b. Disconnect the HEGO sensor and the EEC module.
c. Check the harness for continuity and for possible short circuits to ground.
7. Perform the following tests for code "42" KOER.
a. Check the fuel pressure (Step 4 above) and repair any concerns found.
b. Disconnect the HEGO and check the HEGO heater voltage with the key ON. The absence of power to the HEGO heater will prevent the HEGO from operating properly.
c. Check HEGO signal shorted to either key power or KAPWR @ ignition run circuit (refer to procedures in pinpoint test "H" of the 1991 Engine/Emissions Diagnosis Manual).
d. Check the HEGO heater fuse (10 amp located in the under-dash fuse box). See the Owner Guide in the glove box for exact fuse location.
e. If no harness concerns are found, replace the HEGO.
8. Perform the wiggle test to look for intermittent harness concerns.
a. Disconnect the HEGO sensor and the EEC module.
b. Check the harness for continuity and for short circuits to ground.
c. Check connectors for pin pushouts and bad terminal crimps.
d. If no wiring concerns are found, replace the processor.
Obtain an Authorized Modifications Decal and list the date, dealer number, and summary of alterations performed. Select a prominent place adjacent to the Vehicle Emission Control Information Decal suitable for installing the Authorized Modifications Decal. Clean the area, install the decal, and cover it with a clear plastic decal shield.
PART NUMBER PART NAME CLASS
F1TZ-12A650-Z EEC IV Processor (Cal. B
1-58A-R10)
F1TZ-12A650-Y EEC IV Processor (Cal. B
1-58B-R10)
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under Basic Warranty
Coverage, Emissions
Warranty Coverage
OPERATION DESCRIPTION TIME
920615A Perform Self Test - Step 1 0.5 Hr.
920615B Inspect For Air And/Or 0.2 Hr.
Vacuum Leaks And Repair
As Required - Steps 2 And 3
920615C Test Fuel Pressure - Step 4 0.2 Hr.
920615D Re-run Self Test - Step 5 0.1 Hr.
920615E Inspect For Harness 0.4 Hr.
Concerns. If None, Replace
HEGO - Steps 6 And 7
920615F Inspect For Wiring 0.4 Hr.
Concerns. If None, Replace
Processor - Step 8
DEALER CODING
BASIC PART NO. CONDITION CODE
12A650 92
OASIS CODES: 206000, 690000