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Can Overdrive Malfunction be connected to Alternator Repair

My 2002 Ford Focus was taken in for a replacement of the alternator. After the repair the check engine light is now on and the overdrive is malfunctioning. I now have to turn the O/D off and on manually. I have had the car 6 years and have never touched the O/D button. It won’t shift into 2nd gear unless I turn it off and when I cruising down a hill I have to turn it on because it shifts into low gear.

I don’t see how changing the alternator could cause that but it does appear they caused the problem somehow. If you haven’t been back to the service shop and talked with the manager I would do that. Explain to him that these problems happened after the repair and you would liked to have the vehicle checked over to see if it was their fault. Hopefully he will have the vehicle checked for loose connections or a blown fuse possibly at no extra cost to you. Checking the error codes will most likely shed some light on the trouble also.

What trouble code is the computer sending?? Have the computer scanned and post back with the results. We’ll go from there.


Hey, Transman, several months ago you recommend that I try Berryman b-12, or something like that, in my transmission. Well it has been doing pretty well since but sometimes it is a little slow to shift. Thanks again.

I’ll admit that this is a stretch; but it’s a very cheap stretch: There are a couple of engine sensors which send ac (alternating current) signal to the engine computer. If there is ac in the power supply, or a radiated alternating magnetic field, that could interfere with the signal from the engine sensor.
The test is simple: use an electrical multimeter and measure the output of the alternator. Set the meter to read ac voltage. There should be nearly none. If there is, replace the alternator.