Check engine light trouble code P0340

CARLO.LUNA

MEMBER
2007 LINCOLN NAVIGATOR
5.4L
V8
2WD
AUTOMATIC
215,000 MILES

Trouble code P0340 came on. Already changed sensor twice. One with aftermarket and the other dealer part. Check engine light still on. Had a mechanic take a look and could not find the problem. Wiring is good. Could it be the crankshaft sensor that needs to be replaced?
Please advice and thank you.

5 Replies

BMDOUBLE

MECHANIC
1,139 POSTS

Another cause of this is a faulty alternator. When diodes go bad it will introduce electrical noise in the system. Have your charging system tested, especially the diodes.

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Monday, July 9th, 2018 AT 3:22 PM

CARLO.LUNA

MEMBER
3 POSTS

Hello BMDOUBLE,
Thank you for the reply. Anything else I can do? Would changing the crankshaft sensor make a difference? My alternator and battery are brand new.

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Monday, July 9th, 2018 AT 9:39 PM

BMDOUBLE

MECHANIC
1,139 POSTS

Did this code pop up after or before the alternator was replaced? And is the alternator a motorcraft brand? Symptoms of a crank sensor is no start or shuts off while driving. Basically if your crank sensor signal is not there the engine will not run.

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Tuesday, July 10th, 2018 AT 5:26 AM

CARLO.LUNA

MEMBER
3 POSTS

Code popped up a few months later. Alternator is not Motorcraft. Not sure what else to do. Vehicle is up for smog and renewal before months end with no solution. What more can I check? Just a thought, would a loose timing chain tension-er cause this problem? Any other suggestions? Thank you always.

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Wednesday, July 11th, 2018 AT 10:51 AM

KEN L

MASTER CERTIFIED MECHANIC
43,305 POSTS

If the sensor is good and the wiring has been checked it sounds like the PCM is the problem. I have seen where camshaft codes are caused by timing chain issues by not the crankshaft sensor.

Here is the location of the PCM you can try a used one but chances are you will need to have it programmed must shops can do it for $130.00.

Check out the diagrams (below). Please let us know what happens.

Cheers, Ken

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