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FORD BRONCO -> ELECTRICAL; EEC/PCM, Self-Test, wiring diagrams... -> Electronic Engine Control (EEC); SELF TEST & Diagnostic Trouble Code (DTC), OBD II, etc. -> Malfunction Indicator Light (MIL) & Check Engine Light (CEL)
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Although we initially developed this site for 78-96 Big Broncos, information in many Links also applies to F, E Series & Cars. UPDATE; all Links via web.archive may be down; Copy orig. URL & go to http://replay.waybackmachine.org/ to search for the new archived copy
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DTC P1742 TSB 96-5-16 for 96 Bronco, E & F Series; Application Chart; "...The Check Engine lamp may illuminate and a Code P1742 may be stored in memory. There may be no driveability concerns present. This may be caused by an improper signaling within the Powertrain Control Module (PCM). ACTION: Reprogram or replace the PCM. Refer to the following Service Procedure for details..."
EEC Processor, MIL On with DTC 173 in Continuous Memory w/Pass Code 111 in KOEO & KOER, Replace EEC TSB 92-18-12 for 91-92 5.8L Bronco, Econoline & F Series
Explanation of 3-Digit Codes & MIL TSB 92-24-03 for 91-93 Bronco, F Series and Many Others
Ford Fuel Injection and Electronic Engine Control: How to Understand, Service and Modify, 1988-1993 by Charles O. Probst
Fuse E Blown, ABS Light On, Back-Up Lamps Inoperative, DRLs Inoperative, MIL On, Speedometer Inoperative TSB 95-02-11 for 92-95 Bronco & F Series
Malfunction Indicator Light (MIL) ("Check Engine Light") Illumination; The "Check Engine" lamp may illuminate and a Code P0420 may be stored in memory. There may be no driveability concerns present.TSB 96-15-13 for 96 Bronco, F Series & Econoline w/5.0L
Malfunction Indicator Light (MIL) ("Check Engine Light") Illumination; The "Check Engine" lamp may illuminate and a Code P1742 may be stored in memory. There may be no driveability concerns present.TSB 96-6-9 for 96 Bronco, F Series & Econoline w/E4OD
Malfunction Indicator Light (MIL) Introduction TSB 88-05-07 for 88 Bronco, F series, & all others
MIL On, Inadvertent Self-Test in TSB 95-5-21 for 92-95 Bronco & F Series; "On some vehicles the HO2S wires in the 12A690 (subassembly of the 14B060 battery cable) harness may become chafed and the vehicle could exhibit any one of the following conditions..." READ MORE
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Check Engine Light (CEL) Overview in 92-96; "...The check engine warning indicator comes on when the electronic engine control system is not working properly. The check engine warning indicator comes on briefly when the ignition switch lock cylinder is turned to ON, and should turn off when the engine starts. If the check engine warning indicator does not come on when the ignition switch lock cylinder is turned to ON or if it comes on while the vehicle is moving, the system is malfunctioning..."; .; miesk5 Note; Steve83 advises; "...If the CEL is burned out, connect CEL (C) to a 12V test light, and the light's other terminal to a 12V source on the same vehicle..." read more
Source: by Steve83 (Steve, That dirty old truck) at SuperMotors.net
Check Engine Light (CEL) Overview in a 96; "...The light comes on briefly when you turn the ignition key to ON, but it should turn off when the engine starts. If the light does not come on when you turn the ignition to ON or if it comes on and stays on when you are driving, have your vehicle serviced as soon as possible. This indicates a possible problem with one of the vehicle’s emission control systems. You do not need to have your vehicle towed in. If the light turns on and off at one (1) second intervals while you are driving the vehicle, it means that the engine is misfiring. If this condition persists, damage could occur to the engine or catalytic convertor. Have your vehicle serviced at the first opportunity. You do not need to have your vehicle towed in. If the light turns on and off on rare occasions while you are driving, it means that a malfunction occurred and the condition corrected itself. An example of a condition which corrects itself occurs when an engine running out of fuel begins to misfire. In this case, the Check EngineWarning Light may turn on and will then set a Diagnostic Trouble Code DTC) indicating that the engine was misfiring while the last of the fuel was being consumed. After refueling, the Check Engine Warning Light will turn off after the vehicle has completed three consecutive warmup cycles without a misfire condition occurring.A warm up cycle consists of engine start from a cold condition (engine at ambient temperature) and running until the engine reaches normal operating temperature. On the fourth engine start up, the Check EngineWarning Light will turn off as soon as the engine begins to crank. It is not necessary to have the engine serviced. Under certain conditions, the Check EngineWarning Light may come on if the fuel cap is not properly installed. If the Check EngineWarning Light comes on and you suspect that the fuel cap is not properly installed, pull off the road as soon as it is safely possible and turn off the engine. Remove and replace the fuel cap, making sure it is properly seated. After completing the three consecutive warm upcycles and on the fourth engine start up, the Check Engine Warning Light should turn off. If the light does not go off after the fourth engine restart, have your vehicle serviced by your dealer or a qualified technician..."
Source: by Ford via Hiller Ford
Check Engine Light (CEL) Wiring Diagram in a 94 from EVTM
Source: by Mikey350 at SuperMotors.net
Check Engine Light (CEL; Malfunction Indicator Light (MIL)) Overview in a 96; "...The check engine warning indicator comes on when the electronic engine control system is not working properly. The CHECK ENGINE warning indicator comes on briefly when the key is turned to RUN, and should turn off when the engine (6007) starts. If the CHECK ENGINE warning indicator does not come on when the key is turned to RUN or if it comes on while the vehicle is moving, the system is malfunctioning. NOTE: If the vehicle is equipped with dual fuel tanks (9002), the CHECK ENGINE light may come on if fuel is restricted to the engine or if the fuel flow is momentarily disrupted because of an empty fuel tank before switching to the auxiliary fuel tank. This condition is normal and the CHECK ENGINE light should go off sometime after fuel flow is restored..." from 1996 F-150, F-250, F-350, Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford via thedieselstop.com
Check Engine Light Location & Operation in an 88; "...As soon as you turn the key foreward to start the bronc, the light should come on, then once the truck is started it should come back on for about 3 secs then go out. it\'s actually stealthily hidden not in the guage cluster but in the black info strip on the gear shift side if the dash, just between the upper and lower trim pieces, your abs, low voltage, 4x4 and right signal indicator are there aswell. if the light fails to come on and check, first look closely for a small piece of electrical tape covering the spot where the light should be( the cheapest fix), if not found take the trim piece off and check for a missing bulb( 2nd most common fix) if the bulb is there change it. then it should come on. if the truck doesnt run the light should still come on when you turn the switch to power. if the battery isn't dead..."
Source: by tiresmok at answers.yahoo.com
DTC P1742 TSB 96-5-16 for 96 Bronco, E & F Series; Application Chart; "...The Check Engine lamp may illuminate and a Code P1742 may be stored in memory. There may be no driveability concerns present. This may be caused by an improper signaling within the Powertrain Control Module (PCM). ACTION: Reprogram or replace the PCM. Refer to the following Service Procedure for details..."
Source: by Ford via Chilton
EEC-IV System Has NO Control Over the Following Items; "...Fuel quantity and quality; Damaged or faulty ignition components; Internal Engine Condition - rings, valves, Timing belt, etc.; Starter & Battery circuit; Dual Hall sensor; TFI or DIS module; Distributor condition or function; Camshaft sensor; Crankshaft sensor; Ignition or DIS coil; Engine governor module..."
Source: by Ford via arrc.epnet.com
Failure Mode Effects Management (FMEM) Overview; "...In FMEM mode, the computer is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the computer uses an alternate strategy to maintain reasonable vehicle operation in spite of the fault. The following chart lists the system faults which will turn on the CHECK ENGINE light in this mode. The error code associated with this system fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and vehicle will return to normal vehicle strategy. The error code stored when the light was on was not erased. This code is one of the continuous error codes and can be accessed by running the KOEO self-test..."
Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net
Freeze Frame Data & No Codes; Another advantage of OBD II is the freeze frame data function of the scan tool. Whenever an emissions related DTC is set, the MIL will illuminate and a freeze frame will be set in the PCM’s memory. The freeze frame should contain, but isn’t limited to, the following data: Engine load (calculated) , Engine RPM , Short- and long-term fuel trim, Vehicle speed, Coolant temperature, Intake manifold pressure, Open/closed loop operation, Fuel pressure (if available), DTC; In this generic scan tool feature, you can’t get DTCs. But you can get a serial data stream that will update a minimum of two times a second. More importantly, you will have access to at least 16 data parameters and a 66-frame movie of ECU/PCM data. The most important function of any scan tool is to diagnose intermittent problems. Listed below are my reasons why the movie/snap-shot is so valuable! On slower baud rate systems, [b]an out-of-range sensor may take several frames of data before a DTC is set. But it would still cause a noticeable driveability problem on the vehicle. And it still might not set a DTC. Duplicating the customer’s complaint with a road test and a movie/ snap-shot may be the only way to properly diagnose the vehicle..." READ MORE
Source: by Gary G at asashop.org
Hardware Limited Operation Strategy (HLOS) Overview; "...HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the computer is running on hardware control only. The default strategy for this mode has a minimal calibration just to allow the vehicle to operate until it can be serviced. NOTE: IN HLOS MODE YOU WILL NOT GET ERROR CODES. The MIL light is turned on as a bulb check when the ignition key is first turned ON. The EEC IV computer turns off the bulb as soon as it receives the PIP (crank) signal. If the light stays on during cranking, the computer is not receiving the PIP signal..."
Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net
Malfunction Indicator Lamp (MIL) Overview; "When the PCM detects an emission related DTC during the 1st trip the DTC and engine data are stored in the freeze frame memory. The MIL light is illuminated only when the PCM detects the same emission related DTC after it occurs in two consecutive trips. Once the MIL is illuminated it will only turn off after the PCM detects three trips without any malfunctions occuring. DTC’s that would cause vehicle emissions to exceed the federal limit are capable of illuminating or blinking the MIL during the 1st trip. Diagnostic Trouble Codes capable of illuminating the MIL when detected on the 1st trip: Misfire diagnostic trouble codes, Catalyst diagnostic trouble codes, Closed loop control diagnostic trouble codes For OBD II vehicles, long term and short term fuel trim values will be shown in percentages. Freeze frame will also show fuel trim values as percentages. Fuel trim represents how much compensation the powertrain control module (PCM) must make from ideal conditions. A higher positive value for fuel trim indicates the PCM is commanding more fuel into the engine, this can be caused by vacuum leaks, restricted fuel injectors, etc. A highly negative value indicates a leaning of the engine, possibly caused by leaky injectors, etc. When a freeze frame event is triggered by an emissions related diagnostic trouble code (DTC), the PCM stores various vehicle information as it existed the moment the malfunction occurred. The DTC number along with the engine data can be useful in aiding a technician in locating the cause of the malfunction. Once the data from the 1st trip DTC occurrence is stored in the Freeze Frame memory it will remain there even when the fault occurs again (2nd trip) and the MIL is illuminated. Freeze Frame data will not be displayed after 40 drive cycles have occurred without a fault. Data can be stored in freeze frame for only one event, however the PCM will prioritize what data it will store. For example an EGR malfunction (priority 2) was detected during the 1st trip and the freeze frame data stored. After that, a misfire DTC occurs (priority 1) in another trip, the misfire data will replace the EGR data stored in the freeze frame memory, except after a misfire or fuel injection system DTC, which will not be cleared until 80 consecutive drive cycles have occurred without a fault. OBD II Monitors The OBD II monitors are: • Exhaust gas recirculation (EGR) system monitor • Heated oxygen sensor (HO2S) monitor • Catalyst efficiency monitor • Misfire detection monitor • Fuel system monitor • Comprehensive component monitor Exhaust Gas Recirculation System Monitor The exhaust gas recirculation (EGR) system monitor is a self-test strategy within the powertrain control module (PCM) that tests the integrity of the EGR system. The EGR monitor uses an EGR temperature sensor to detect a malfunction in any of the EGR system components and/or control circuitry. Heated Oxygen Sensor Monitor OBD II regulations require monitoring of the upstream heated oxygen sensor (HO2S) to detect if the deterioration of the sensor has exceeded emission thresholds. An additional HO2S is located downstream of the warm-up three way catalytic converter (WU-TWC) to determine the efficiency of the catalyst. Although the downstream HO2S is similar to the type used for fuel control, it functions differently. The downstream HO2S is monitored to determine if a voltage is generated. That voltage is compared to a calibrated acceptable range. The catalyst efficiency monitor is a self-test strategy within the powertrain control module (PCM) that uses the downstream heated oxygen sensor (HO2S) to determine when a catalyst has fallen below the minimum level of effectiveness in its ability to control exhaust emissions. Misfire is defined as the lack of proper combustion in the cylinder due to the absence of spark, poor fuel metering, or poor compression. Any combustion that does not occur within the cylinder(s) at the proper time is also a misfire. The misfire detection monitor detects fuel, ignition or mechanically induced misfires. The intent is to protect the catalyst from permanent damage and to alert the customer of an emission failure or an inspection maintenance failure by illuminating the malfunction indicator lamp (MIL). When a misfire is detected, special software called ‘‘Freeze Frame’’ data is enabled. The Freeze Frame data captures the operational state of the vehicle when a malfunction is detected from misfire detection monitor strategy. The fuel system monitor is a self-test strategy within the powertrain control module (PCM) that monitors the adaptive fuel table. The fuel control system uses the adaptive fuel table to compensate for normal variability of the fuel system components caused by wear or aging. During normal vehicle operation, if the fuel system appears ‘‘biased’’ lean or rich, the adaptive fuel table will shift the fuel delivery calculations to remove the bias. The comprehensive component monitor is a self-test strategy within the powertrain control module (PCM) that detects malfunctions of any electronic powertrain component or system that provides input to the PCM and is not exclusively an input to any other OBD II monitor."
Source: by Ford motorcraftservice.com
Malfunction Indicator Light (MIL) w/No Self Test Codes TSB 92-24-3 for 91-93
Source: by Ford via miesk5 at comcast.net
Malfunction Indicator Light (MIL) Introduction TSB 88-05-07 for 88 Bronco, F series, & all others
Source: by Ford via Steve83 (Steve, That dirty old truck) at fourdoorbronco.com
NO CODE; IN HLOS MODE YOU WILL NOT GET ERROR CODES. Hardware Limited Operation Strategy (HLOS) Overview; "...HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the computer is running on hardware control only. The default strategy for this mode has a minimal calibration just to allow the vehicle to operate until it can be serviced. NOTE: IN HLOS MODE YOU WILL NOT GET ERROR CODES. The MIL light is turned on as a bulb check when the ignition key is first turned ON. The EEC IV computer turns off the bulb as soon as it receives the PIP (crank) signal. If the light stays on during cranking, the computer is not receiving the PIP signal..."
Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net
OBD-II PIDs On Board Diagnostics "Parameter IDs"; "...are codes used to request data from a vehicle, used as a diagnostic tool. These codes are part of SAE standard J/1979, required to be implemented in all cars sold in North America since 1996. Typically, an automotive technician will use PIDs with a scan tool connected to the vehicle's OBD-II connector. The technician enters the PID. The scan tool sends it to the vehicle's bus (CAN, VPW, PWM, ISO, KWP. After 2008, CAN only). A device on the bus recognizes the PID as one it is responsible for, and reports the value for that PID to the busThe scan tool reads the response, and shows it to the technician..." READ MORE
Source: by wikipedia.org
Overview ("Check Engine Light")
Source: by obdii.com
Oxygen Sensor, Malfunction Indicator Light (MIL) Eliminator for a Mustang, but similar; make your own with Radio Shack parts, Scroll to bottom; "...The MIL eliminator is simply a resistor and capacitor circuit placed in the O2 sensor harness that sends the computer the lean signal (300mV) it expects to see. Below we've shown you how to install the MIL Eliminators, or build your own, to ensure check engine light free driving..."
Source: by fordmuscle.com
Oxygen Sensor, Malfunction Indicator Light (MIL) Eliminator Resistor pic in a 95
Source: by rem 243 (Drew A) at SuperMotors.net
Parameter Identification (PID); "...The Parameter Identification (PID) mode allows access to powertrain control module (PCM) information. This includes analog and digital signal inputs and outputs along with calculated values and system status. There are two types of PID lists available and both are used throughout this manual. The first is the Generic (J1979) OBDII PID list. This is a standard set of PIDs for all manufacturers all scan tools must be able to access. The second is a Ford specific (J2190) list which can be accessed by an adequate scan tool. When accessing any of these PIDs, the values will be continuously updated. The Generic or Ford PID list provides definitions and values in appropriate units. For more information, refer to the Society of Automotive Engineers (SAE) J2205 document. Generic OBD II PID List; from 2003/2004 Ford Factory Service Manual. READ MORE
Source: by paladinmicro.com
Self Test - Scan Tool Won’t Initiate Self-Tests Troubleshooting in EEC-IV; SIG-RTN, Self-Test Output circuit, etc.; miesk5 Note; Steve83 advises; "...If the CEL is burned out, connect CEL (C) to a 12V test light, and the light's other terminal to a 12V source on the same vehicle..."
Source: by Ryan M (Fireguy50) at fordfuelinjection.com
The On-Board Diagnostic (OBD) Executive; "...is a portion of the PCM strategy that manages the sequencing and execution of all diagnostic tests. It is the "traffic cop" of the diagnostic system. Each test/monitor can be viewed as an individual task, which may or may not be able to run concurrently with other tasks. The Diagnostic Executive enables/disables OBD monitors in order to accomplish the following: • Sequence the OBD monitors such that when a test runs, each input that it relies upon has already been tested. • Controls and co-ordinates the execution of the individual OBD system monitors: Catalyst, Misfire, EGR, O2, Fuel, AIR, EVAP and, Comprehensive Component Monitor (CCM). • Stores freeze frame and "similar condition" data • Manages storage and erasure of Diagnostic Trouble Codes as well as MIL illumination • Controls and co-ordinates the execution of the On-Demand tests: Key On Engine Off (KOEO), Key On Engine Running (KOER), and the Output Test Mode (OTM). • Performs transitions between various states of the diagnostic and powertrain control system to minimize the effects on vehicle operation. • Interfaces with the diagnostic test tools to provide diagnostic information (I/M readiness, various J1979 test modes) and responds to special diagnostic requests (J1979 Mode 08 and 09). The diagnostic also executive controls several overall, global OBD entry conditions. The Diagnostic Executive waits for 4 seconds after the PCM is powered before initiating any OBD monitoring. The Diagnostic Executive suspends OBD monitoring when battery voltage falls below 11.0 volts..."
Source: by Ford