Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSFORD1991RANGER 2WD L4-140 2.3L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULETECHNICAL SERVICE BULLETINSCUSTOMER INTERESTMIL ON/CODE 41 DISPLAYED
1991 Ford Ranger 2WD L4-140 2.3L SOHC
MIL ON/Code 41 Displayed
1991 Ford Ranger 2WD L4-140 2.3L SOHCSECTION MIL ON/Code 41 Displayed
91ford25
Article No.
91-20-11
10/02/91
^ EEC IV - MALFUNCTION INDICATOR LIGHT (MIL) - 2.3L OHC - ACTIVATED WITH NO FAULT PRESENT AND CONTINOUS MEMORY SERVICE CODE "41" DISPLAYED
^ LAMP - MALFUNCTION INDICATOR LIGHT (MIL) - 2.3L OHC - ACTIVATED WITH NO FAULT PRESENT AND CONTINOUS MEMORY SERVICE CODE "41" DISPLAYED
LIGHT TRUCK: 1990-91 RANGER
CALIBRATION: 0-50S-R00, 05-50T-R10, 0-49S-R00, 0-049T-R10
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.
ISSUE: A limited range of adaptive fuel control in the subject calibrations may set a Continuous Memory Service Code "41" and activate the Malfunction Indicator Light (MIL) with no fault present.
ACTION: If the MIL Light is lit and the KEY ON/KEY OFF (KOEO) Self-Test produces only Continuous Memory Code "41" (11-10-41), perform the following service procedure.
1. Run KEY ON Engine Running Self-Test and service any codes received using procedures from the Engine/Emissions Diagnosis Manual.
2. Clear the Continuous Memory by initiating KOEO Self-Test and ungrounding STI when service codes begin to be displayed.
NOTE: DO NOT DISCONNECT THE BATTERY OR THE 60-PIN PROCESSOR CONNECTOR.
3. Have the customer drive the vehicle for one week to confirm that the MIL is no longer lit.
4. If Continuous Memory Code "41" reappears after additional mileage has been accumulated and all diagnostic procedures have been completed, replace the EEC IV 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
F0PZ-12A65O-MA EEC IV Processor (Auto. B
Trans., Cal. 0.50S-R00 and
0-50T-R10)
F0PZ-12A650-LA ECC IV Processor (Manual B
Trans., Cal. 0-49S-R00 and
0-49T-R10)
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under Basic Warranty
Coverage, Emissions
Warranty Coverage
OPERATION DESCRIPTION TIME
912011A Perform Test And Clear 0.5 Hr.
Codes
912011B Replace Processor 0.3 Hr.
DEALER CODING
BASIC PART NO. CONDITION CODE
12A650 09
OASIS CODES: 203000, 206000, 690000
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.