PCM - MIL ON/Intermittent and DTC 121
Article No.94-16-18
08/10/94
MALFUNCTION INDICATOR LAMP - INTERMITTENT/CONTINUOUS MALFUNCTION INDICATOR LAMP (MIL) AND DIAGNOSTIC TROUBLE CODE (DTC) 121 IN COLD AMBIENTS - 2.3L OHC ENGINE - EQUIPPED MODELS BUILT FROM JOB-1 1994 THROUGH 3/18/94
LAMP - MIL - INTERMITTENT/CONTINUOUS OPERATION AND DIAGNOSTIC TROUBLE CODE (DTC) 121 IN COLD AMBIENTS - 2.3L OHC ENGINE - EQUIPPED MODELS BUILT FROM JOB-1 1994 THROUGH 3/18/94
LIGHT TRUCK:
1994 RANGER
ISSUE:
An intermittent or continuous Malfunction Indicator Lamp (MIL) illumination with Diagnostic Trouble Code (DTC) 121 stored without any driveability concerns during cold ambient temperatures may occur in some 2.3L trucks. This may be caused by the Powertrain Control Module (PCM) erroneously identifying an out-of-range Throttle Position (TP) sensor. The condition is more prevalent during cold ambient temperatures and when the air density is heavier.
ACTION:
Install a service replacement PCM which has revised calibrations to compensate the relationship between TP sensor signal and air density during cold weather. Refer to the following procedure for service details.
NOTE:
THIS TSB ARTICLE IS NOT APPLICABLE FOR CALIFORNIA MANUAL TRANSMISSION CALIBRATIONS: 4-49R-R00, 4-49T-R00, AND 4-49M-R05.
DIAGNOSTIC TROUBLE CODE (DTC) CHECK
1. Perform normal diagnosis to be sure that no other faults are present. Refer to the Powertrain Control/Emissions Diagnosis (PC/ED) Car/Truck Service Manual - OBD 1 for MIL concerns.
a. Check for DTC's as directed.
b. If any other DTC's are found, they MUST be repaired before proceding.
c. Verify calibration number and PCM part number.
POWERTRAIN CONTROL MODULE (PCM) REPLACEMENT
Install a service replacement PCM. Refer to the PCM Replacement Chart included in this article.
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.
Parts Block
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage And Emissions Warranty Coverage
OPERATION DESCRIPTION TIME
941618A Perform EEC-IV Quick Test, 0.8 Hr.
Replace PCM, Perform
Final Quick Test
DEALER CODING
BASIC PART NO. CONDITION CODE
12A650 08
OASIS CODES: 206000, 623000, 698298