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Ron
Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 23001
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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Mustang GT: i keep getting check eng light. i scanned the comp.

Customer Question

i keep getting check eng light. i scanned the comp. and it gave me p340 what do i need to do
Submitted: 1 year ago.
Category: Ford
Expert:  Jan Andersson replied 1 year ago.
Hi, this could be the known issue with a bad (going bad) alternator, there is a tech service bulletin for it. Most little shops would not know how to test the alternator this way or would not have a tester capable of detecting the problem, "Generator frequency". Looks like you need a trip to the dealership. You might want to return everything as close to stock as you can before you go, for any warranty or liability issues like "Oh you messed with the computer now we won't touch it". Some are more touchy about t thatn others, depends on who you talk to . Here is the TSB: 06-02-09 2004-2006 MULTIPLE VEHICLES - DTC P0340/P0344/P0345/P0349 - 4.6L 3V AND 5.4L 3VSOME 2005-2006 F-SUPER DUTY AND EXPEDITION/ NAVIGATOR AND 2004-2005 F-150, EQUIPPED WITH 5.4L 3V ENGINE, AND 2005-2006 MUSTANG GT VEHICLES, EQUIPPED WITH 4.6L 3V ENGINE, MAY EXHIBIT A DIAGNOSTIC TROUBLE CODE (DTC) P0340 AND/ OR P0344; OR 2006 EXPLORER 4DR/ MOUNTAINEER EQUIPPED WITH A 4.6L 3V ENGINE MAY EXHIBIT A DTC P0345 AND/ OR P0349. THIS MAY BE DUE TO A MALFUNCTIONING DIODE OR OPEN PHASE CONNECTION IN THE GENERATOR. PERFORM A GENERATOR FREQUENCY TEST TO DIAGNOSE CAUSE OF CONCERN. DO NOT REPLACE THE GENERATOR UNLESS A FREQUENCY TEST INDICATES A FAULT. THIS TSB PROVIDES STEP-BY-STEP DIRECTION FOR PERFORMING A GENERATOR FREQUENCY TEST USING THE WDS OSCILLOSCOPE FUNCTION.See TSB for complete detailsEFFECTIVE DATE: 01/20/2006Printable View (128 KB) TSB06-2-9DTC P0340/P0344/P0345/P0349 - 4.6L 3V AND 5.4L 3VPublication Date: January 19, 2006FORD:2005-2006 Mustang2004-2005 F-1502005-2006 Expedition, F-Super Duty2006 ExplorerLINCOLN:2005-2006 NavigatorMERCURY:2006 MountaineerThis article supersedes TSB 05-23-17 to update the vehicle line coverage. ISSUE:Some 2005-2006 F-Super Duty and Expedition/Navigator and 2004-2005 F-150 vehicles, equipped with 5.4L 3V engine, and 2005-2006 Mustang GT vehicles, equipped with 4.6L 3V engine, may exhibit a diagnostic trouble code (DTC) P0340 and/or P0344; or 2006 Explorer 4dr/Mountaineer equipped with a 4.6L 3V engine may exhibit a (DTC) P0345 and/or P0349. This may be due to a malfunctioning diode or open phase connection in the generator.ACTION:Perform a generator frequency test to diagnose cause of concern. Do not replace the generator unless a frequency test indicates a fault. This TSB provides step-by-step directions for performing a generator frequency test using the WDS oscilloscope function.SERVICE PROCEDURENOTE:USING THE OSCILLOSCOPE TO MEASURE PEAK-TO-PEAK VOLTAGE IS NOT A GOOD INDICATOR OF A FAULTY GENERATOR.NOTE:ENSURE THERE IS NO BATTERY CHARGER CONNECTED TO THE VEHICLE.Ensure the connections to the battery terminals, engine grounds, and generator B+ are clean and secure.Attach WDS battery cable clamps to battery/battery cables.Turn on WDS.Select the Toolbox Icon, (upper left of WDS screen).Select Oscilloscope and then click OK.Select Channel 1, Auto, Generator Ripple.Select Calculations, Channel 1, Frequency.Select Calculations again.Push the RUN/STOP button. A waveform should display on the screen.Start the vehicle and leave at idle (engine speed less than 800 RPM).Turn on vehicle loads (high beams, blower set on high, heated seats, defroster, etc).Examine the frequency reading on WDS.NOTE:WDS CAN CALCULATE THE FREQUENCY AUTOMATICALLY. THE CALCULATED FREQUENCY IS LOCATED ON THE LOWER LEFT AREA OF THE OSCILLOSCOPE SCREEN. SOMETIMES THE FREQUENCY CANNOT BE CALCULATED BECAUSE THE WDS CANNOT RECOGNIZE AND MEASURE PEAK VALUES. IF THE WDS CANNOT CALCULATE THE FREQUENCY, IT WILL DISPLAY "INVALID" WHERE THE FREQUENCY READING SHOULD BE. THIS IS NORMAL IF THE RIPPLE VOLTAGE IS TOO LOW.For a proper visible wave pattern, adjust the voltage scale and time scale until a good wave pattern is visible. Typically, a setting of 1mS/div and 100mV/div is a good starting point and can be adjusted as necessary.Run vehicle until signal is steady. Then select the "RUN/STOP" button to freeze the waveform.Determine if the generator is faulty based on frequency measurement:NOTE:FREQUENCY IS DEPENDENT ON ENGINE RPM. PERFORM ALL TESTS AT IDLE OR FREQUENCY READINGS WILL BE INACCURATE.Compare the WDS saved waveform to the sample waveforms in Figure 1. If measured ripple frequency is lower than 500 Hz, then generator is faulty and should be replaced. If generator is not faulty proceed to Step 16.If frequency calculation cannot be made by WDS, it can be calculated manually. See MANUALLY CALCULATE FREQUENCY. If calculated ripple frequency is lower than 500 Hz, then generator is faulty and should be replaced. If generator is not faulty proceed to Step 16.MANUALLY CALCULATE FREQUENCYCount the number of complete voltage dips over a given range of divisions on the scope traceDivide the number of voltage dips by the number of divisions to get the average voltage dips/divisionDivide the value in Step 2 by the time scale (e.g. 1mS/div = .001 sec/division) to get frequencyNOTE:THIS METHOD OF CALCULATING FREQUENCY IS SLIGHTLY DIFFERENT THAN THE METHOD USED BY WDS, SO THE FREQUENCY MEASUREMENT VS. CALCULATED MAY BE SLIGHTLY DIFFERENT.If the frequency test does not indicate a fault with the generator, proceed with normal Powertrain Controls/Emissions Diagnosis (PC/ED) diagnostics for the DTC. For F-Super Duty vehicles only, if the DTCs are still present after diagnostics, reprogram the powertrain control module (PCM) to the latest calibration using WDS release B38.11 and higher or B39.2 and higher. Calibration files may also be obtained at www.motorcraft.com. This new calibration is not included in the B39 CD. (DO NOT REPROGRAM EXPEDITION/NAVIGATOR, F-150, MUSTANG, OR EXPLORER/MOUNTAINEER).PART NUMBERPART NAME5L7Z-10346-CAGenerator - Standard Duty - Expedition/Navigator5L7Z-10346-BAGenerator - Heavy Duty - Expedition/Navigator6L3Z-10346-AAGenerator - F-1506C3Z-10346-AAGenerator - F-Super Duty6R3Z-10346-DAGenerator - Mustang6L2Z-10346-AAGenerator - Explorer/MountaineerWARRANTY STATUS:Eligible Under Provisions Of New Vehicle Limited Warranty CoverageOPERATIONDESCRIPTIONTIME060209A2005-2006 Expedition/Navigator 5.4L 3V: Diagnose Generator Using WDS, If Generator Is Found Defective Replace Generator (Do Not Use With 10346A, 10200A)0.8 Hr.060209B2005-2006 Super Duty, 2004-2005 F150 5.4L 3V: Diagnose Generator Using WDS, If Generator Is Found Defective Replace Generator (Do Not Use With 10346A, 10200A)0.9 Hr.060209C2005-2006 Super Duty, 5.4L 3V: Diagnose Generator Using WDS, If Generator Is Found To Be Functioning Properly Reprogram The Powertrain Control Module (Do Not Use With 10346A, 10200A, 12650D, 12650D84)0.6 Hr.060209D2005-2006 Mustang 4.6L 3V: Diagnose Generator Using WDS, If Generator Is Found Defective Replace Generator (Do Not Use With 10346A, 10200A, 9926A, 12650D, 12650D84)0.8 Hr.060209E2006 Explorer/Mountaineer 4.6L 3V: Diagnose Generator Using WDS, If Generator Is Found Defective Replace Generator. (Do Not Use With 10346A, 10200A, 9926A, 12650D, 12650D84)1.1 Hrs.DEALER CODINGBASIC PART NO.CONDITION CODE1034642

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