Rick's Free Auto Repair Advice

P0340 Ford

Fix a P0340 camshaft position sensor trouble code on Ford

Ford has issued a service bulletin #05-23-17 to address a problem with trouble code P0340 Ford dealing with the camshaft position sensor. The bulletin pertains to the vehicles listed below

2005-06 Mustang

2004-05 F-150

2005-06 Expedition, F-Super Duty

2006 Explorer

2005-06 Navigator

2006 Mountaineer


The P0340 Ford trouble code may appear on the 5.4L engines in the F-Super Duty, Expedition/Navigator, and F-150 and the 4.6L engine in the Mustang GT and Explorer/Mountaineer.


P0340 Camshaft Position Sensor Circuit Malfunction


In addition to the P0340 code, the problem may also trigger a P0344, P0349, or P0345 camshaft intermittent trouble code


P0344 Camshaft Position Sensor Circuit Intermittent


The problem is caused by excess AC ripple. All alternators generate AC voltage and then convert the AC to DC using rectifier diodes. However, if the diodes aren’t doing their job, the AC voltage can be induced into the cables under the hood and interfere with sensor signals coming into the PCM.


So Ford wants you to perform a generator frequency test to diagnose the problem. They warn not to replace the generator (alternator) unless if fails the frequency test. The test is done at 800 RPM and involves turning on loads like the high beams, blower set to high, heated seats, defroster, etc.


The Ford WDS tool computes the frequency values automatically. It compares the AC ripple frequency and if the frequency is less than 500Hz, then the alternator should be replaced.


The test can be completed with a digital storage oscilloscope. Just measure the voltage dips over a given range of divisions on the scope trace. Divide the number of dips by the number of divisions to get an average voltage dip. Then divide that value by the time scale (1 millsecond per division = .001 sec/division) to get the frequency


If you replace the alternator and still find the trouble codes, you must update the PCM software to the latest version

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Posted on by Rick Muscoplat

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