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OD light flashing after new transmission

Hello. We are having an odd problem with our 2009 Mustang. We purchased it two years ago. Within the first six months, we had transmission problems. The OD light was blinking and it was making a horrible noise. We took it to a shop and had the transmission rebuilt. No further issues for about six months. We thought we were in the clear until we went for a drive and it started making that same noise as last time. We immediately knew it was the transmission again. This time we decided to have it towed to a very good friend that runs a transmission shop. He confirmed it was the transmission. We opted for a brand new one this time, hoping that it would resolve the issue once and for all. All good for a month. Now the OD light is blinking again. The car isn’t making any noises this time though, and it seems to be shifting fine. The only thing we have done since the new transmission is we replaced the radio a few days ago. There is also an ongoing issue with the AC that we are currently working out. Is there a possibility that the OD wire is bad? I can’t imagine how a second transmission could go bad in the last two years. Any input would be greatly appreciated. Thanks!

Was it a Ford transmission that was installed?

Tester

It was. We were told it was for a GT

Both the V6 and the GT used the same automatic transmission (5R55S) from 2005-2010 IIRC.

Right. We have the V6 and that’s exactly what we were told.

If I had a friend with a transmission shop, I would ask them.

Well?

All you did was install the same transmission with the same defect.

If it were me, I would have installed a remanufactured transmission.

These transmissions when remanufactured usually include updates that eliminate the problem areas of the transmission so the transmission lasts longer than the original.

Tester

We are really about to throw in the towel and just get rid of it. We don’t want to because of all the money that’s been dropped into the thing, but I can’t see putting a third transmission in it. I wish we would have known what you just said before hand.

Well, it’s an '09 so any design defects should be reasonably well understood. You had the first one rebuilt in 2018 so any improvements should have been included. It failed and you opted for a new replacment in what 2019? Doubt that new one has been sitting on a shelf since 2009 so it should have been built with upgrades as well.

I wouldn’t assume you have another failing tranny just yet. Get it looked at and scanned for codes. It may be something less drastic.

One thing that can lead to replacements going bad is if they don’t flush the lines and cooler prior to installing the new one. Any residual debris in them can foul up the new trans…

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Don’t you have a warranty on the replacement transmission and work?

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Yes, I do. I’m waiting for a call back from my friend that put the last transmission in because the warranty is through him. We’ve paid roughly $6k so far for both the rebuilt and new transmissions combined to date. I know I won’t get charged this time around because of the warranty. The issue is that the shop is about an hour and 45 minutes from my house. I really don’t want to get it towed there again and deal with picking it up when it’s done if it’s something like a short in the wire or something. We did have an issue two weeks ago with the light blinking. Had it towed there and it did end up being the od wire. He said he fixed it though and it was gone when we picked it up. Now it’s back. I sent him a message asking where the problem with the wire was. I’m hoping it’s something we can handle on our own this time… unless it’s the tranny again. Then I’ll have to make the arrangements

yes, towing sucks, but perhaps your insurance will pick that up.