FORD PCM CONTROLLED CHARGING SYSTEM

1 MAY 2007 ford PCM CONTROLLEDCHARGING SYSTEMThe ford PCM (Powertrain Control Module) CONTROLLED CHARGING SYSTEM that is used onmany of its vehicles from 1999 up to thepresent has many benefits. First and mostimportant is improved battery life. This isbecause the PCM can calculate batterytemperature and adjust the chargingsystem voltage based on that temperature,preventing overcharging or additional benefit is improved engineperformance at wide open throttle wherethe PCM can lower the CHARGING SYSTEM svoltage output to reduce alternator in mind that this feature has a timeout limit so as not to create a batterydischarge third benefit is improved idle PCM has the ability to adjust chargingsystem voltage according to the electricalload, resulting in a much quicker responsein order to maintain a stable idle.

2 The finalbenefit is reduced cranking effort, wherethe PCM will lower the voltage outputduring cranking, which reduces starter loadand improves start up PCM monitors alternator load on theGEN-MON/GFS wire in the form of afrequency or duty cycled signal which isdirectly proportional to the electrical example, 97% indicates a full load,while less than 6% indicates no load asindicated through a scan tool reading onthe GFS (Generator Field Sense) PID(Parameter Identification Data). This signalis sent by the alternator to the PCM so thatthe PCM can determine the vehicle selectrical load so that it may maintain theproper voltage set point. This signal is alsoused by the PCM to determine the loadplaced on the engine by the chargingsystem so that the PCM can properlycontrol idle speed.

3 The PCM controls the alternator regulatorthrough the GEN-COM/GENFDC terminal/wire. A command signal is sent bythe PCM to the regulator indicating thedesired voltage set point. Inputs such as:throttle position, coolant temperature, air temperature, and vehicle speed are consideredwhen calculating the voltage set signal is transmitted by way of pulsetrains that are transmitted at least onceevery five seconds. The frequency/dutycycle of the pulse trains determines thevoltage set point. The PCM has the ability to store codes ifthere is a problem within the codes are: P1244 - Alternator load input lowP1245 - Alternator load input highP1246 - Alternator load input failedThese codes are set when the PCMmonitors a mismatch with the alternatorinput compared to what the vehicle loadshould be during normal the PCM detects a CHARGING systemproblem, it will broadcast a low voltagetelltale network communication messagewhich tells the instrument cluster toilluminate the charge indicator charge light will illuminate if the PCMfails to see a signal from the alternator loadinput (GEN-MON/GFS) for a period of time ofapproximately 1/2 of a second.

4 The indicatorwill also be illuminated if there is an overchargevoltage condition. The regulator set point( volts) is established by a temperaturesensor that calculates battery sensor is located inside of the regulatoritself. The PCM will control the voltage setpoint through the GEN-COM(GEN/FDC) wire depending on what the regulatorreports to the years ford has changed theacronyms on the SYSTEM , but relatively thedefinitions are the same. There are fourwires going into this alternator. First is theheavy gauge wire that is attached to themain post of the alternator that goes rightto the battery. The remaining wires are in athree terminal connector (refer to thediagram) that has the SENSE circuit whichallows the regulator to read the actualvoltage of the battery, a GEN-COM orGENRC (Generator Field Command) circuitfor the PCM to control the regulator andlastly a GEN-MON or GENLI (GeneratorMonitor) circuit for feedback informationback to the PCM.

5 Acronyms/Definitions for components usedin this SYSTEM are identified (depending onthe year of manufacture) as follows: GEN-COM/GENFDC would relatively meanthe same,- GEN-COM/GENRC generator field command- GENFDC generator field control outputFor the GEN-MON/GFS/GENLI- GEN-MON generator monitor- GFS generator field senseTo test this SYSTEM , first disconnect thethree-terminal connector. Use a schematicto identify the SENSE, GEN-COM and GEN-MON circuits. With the ignition key on,engine off and the alternator connectordisconnected, your SENSE wire shouldhave battery voltage at the connector. Next,the GEN-COM wire should have zero volts,and the GEN-MON wire should have ninevolts at the connector.

6 The GEM-COMsignal is duty cycled to ground by the PCMwhile the regulator supplies battery voltageto this circuit, so if the PCM does not pullthe voltage low on this circuit, the regulatorwould not turn on and then the generatorwould not charge. When this circuit ischecked with a meter set up for frequency,if it registers 125 Hz., the SYSTEM shouldcharge at 14 volts. At 102 Hz, chargingsystem voltage should be at volts. Andat 250 Hz, it should be at 13 volts. For theGEN-MON circuit, if the circuit goesopen/short to ground or to power, it wouldset a P1246, so checking this circuit witheither a frequency or duty cycle meterwould be acceptable as long there is areading on you check our trouble shooting list,make sure that you have the correctalternator for your vehicle.

7 We have hadmore CHARGING SYSTEM problems becausean incorrect alternator was installed. Also, ifyou do decide to replace the alternator,double check with your supplier that youare getting the correct alternator for yourspecific vehicle, so that you will avoidunnecessary diagnostics. MAY 2007 Here s a list of what to look for when you get atrouble code:P1244- Alternator Load High Input- Input is higher than the load should be during normal : Battery shortedGEN-MON circuit shorted to circuit shorted to positive cable has an open circuit prior to start circuit open prior to start Alternator Load Input Low- Input is lower than the load should be during normal operation, or the alternator has no.

8 GEN-COM circuit shorted to circuit shorted to groundBattery positive cable has an open circuit during SYSTEM voltage due to battery or alternator alternator due to being bad or a broken Alternator Load Input Failed- For some reason, the PCM is not receiving the load frequency signal from the : Any of the wires to the alternator for: shorts to ground or, short to power, or open alternator, or a broken belt. Faulty Jance- ford Specialist