Radio and interior lights cut out above ~5k rpm

Discussion in '2005+ Mustang GT 4.6L Tech' started by Noster239, Aug 18, 2019.

  1. Noster239

    Noster239 Junior Member

    Already resolved the issue, but wanted to leave this here in case anyone else encounters something similar.

    Started with check engine light and code P0340. P0340 is for the camshaft position sensor but is known to be related to a faulty alternator. (You can find more info on this elsewhere)

    Replaced my alternator with a remanufactured part. Worked perfectly and got rid of the check engine light. However, it did create a new issue that I wasnt able to find any information on. Above ~5k rpm (driving or clutch in) my interior lights would flicker off, traction control and abs lights would come on, and my radio would turn off and suddenly back on. Engine never died and the dash lights, headlights, and taillights stayed on. Took the alternator back to the parts store and it tested perfectly fine. Accordingly I was pretty worried I had just screwed up the install or uncovered a new underlying issue elsewhere in the car. Took some convincing but I talked the manager into warranting the part. New alternator in, problem gone.

    I doubt this is a situation hardly anyone else will encounter, but not being able find any info on it myself and the alternator testing perfect made it a hard sell to the parts counter.

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  2. 07 Boss

    07 Boss forum member

    That's because the fault does not show on a regular alternator test. You need to test the diode specifically. Regular test just shows we're producing amperage and voltage.
  3. 07gts197

    07gts197 forum member

    I had a similar problem when I had my 98 p71 vic. Sometimes when it was cold out Id turn the car on and only the headlights would work and they would flicker ever so slightly. After about 5 minutes of driving there would be a click and everything would start working normally again. Then it would do it in normal temps so I got curious one day and finally caught it in the act and put my meter on it. It was putting out around 15 volts! I swapped the alternator and problem solved.

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  4. dark steed

    dark steed Resident noob

    You are lucky that’s all it happened! I put on a remanufactured alternator – I think it was number three or four - and when went WOT everything suddenly got brighter and then it blew both headlight bulbs, all of the bulbs in the radio display, it even got the auxiliary line in for my shaker 500 radio. Luckily I had my highbeams on so it didn’t get my fog lights, because I was coming up on a sharp curve rapidly.
    I got the O’Reilly auto parts lifetime warranty alternator when the OEM one went out. The manager even warrantied out both lightbulbs when I took the alternator back.