2006 Mustang GT Emissions Light and DTC P0340. - Ford Mustang Forum
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post #1 of 6 (permalink) Old 11-13-2013 Thread Starter
Moastng's Avatar
Joined: Nov 2013
Location: San Marcos
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2006 Mustang GT Emissions Light and DTC P0340.

I recently took my 2006 Mustang GT to Pep Boys for an oil change. They also did a transmission fluid/filter change and replaced the air filter. The next morning, my Emission light was on. I took it back to Pep Boys thinking they had caused the problem. Their diagnosis showed P0340 and they said that my alternator needs to be replaced. The printout they gave me shows that the charging system has a ripple problem. It seems odd that is was fine until they worked on it. Mileage is about 65,000.

Also, I don't understand what the alternator has to do with emissions.

Anybody have any suggestions?

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post #2 of 6 (permalink) Old 11-13-2013
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This is why I don't let anyone else work on my cars.

Yeah no idea either how your alternator could cause an emissions problem.

I personally would check the alternator with the voltage tester and if it's charging, unplug the battery overnight and reset the code and if it never comes back, don't worry about it.

Not to insult anyone but to many times I've taken my car to autozone, pepboys or even large dealerships for simple things like oil changes or to test a battery and they tell me the wrong information or have the dumbest person there change the oil and they don't tighten the filter all the way or forget to put the cap on.

2004 F-250 V10 Crew Cab with 6 inch lift

1996 Mustang GT V8

1995 Mercury Sable
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post #3 of 6 (permalink) Old 11-14-2013 Thread Starter
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Thanks for the reply. We disconnected the battery and the light went out and hasn't come back -- yet. Hopefully it won't.
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post #4 of 6 (permalink) Old 11-14-2013
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At the risk of beating a dead horse, P0340 isn't an emission DTC. It's a cam sensor DTC which is vital to the operation of a OHC motor. This goes double if the motor has variable cam timing.

Excessive alternator ripple (bad diode) is well known to cause false cam related DTC's. Hence why there's a generally accepted suggestion to have the alternator tested BEFORE replacing a cam sensor.

However, I agree that if the code doesn't back, then move on.

P0340 - Camshaft Position Sensor A Circuit (Bank 1 or single sensor)

CMP circuit open
CMP circuit short to GND
CMP circuit short to voltage
SIG RTN open (VR sensor)
CMP GND open (Hall-effect sensor)
CMP circuit short to CMP2 circuit (if equipped)
CMP incorrectly installed (Hall-effect sensor)
Damaged CMP sensor shielding
Damaged CMP sensor
Damaged PCM

2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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post #5 of 6 (permalink) Old 11-14-2013
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Probably just a coincidence, having your car at Pep Boys and then getting the P0340. For future reference though, don't ever take your vehicle there - they are a well established group of clowns. Google "Pep Boys reviews" for more; my employer has a fleet acct with them and ohhhh the stories I could tell.

Anyway, what's in the above post from wmburns is dead accurate. When the light comes back on (and it probably will) just go buy a new alternator. My bro in law's '03 GT had the same code a year ago (along with P0316 - misfire at startup), I reset it once or twice and after that it went away for good. Until a year later when his alternator just failed completely.

2001 GT Convertible
/1967 Coupe
All the usual bolt-on's /200 I6, C4

And a few Explorers too... 2008 4.0 XLT 4x2, 1996 XLT 5.0 4x2, 2003 Sport Trac XLT 4.0 4x4
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post #6 of 6 (permalink) Old 11-14-2013
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I agree with above, if it doesn't come back, move on. As far as pep boys, I might let them work on my lawnmower. If I didn't have a lawn.

The artist formerly known as SteedaMatt.
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