# 2002 F550 flashing od light, limp mode



## BlownAway (Oct 25, 2011)

Here's an issue that we can't seem to diagnose: The last snow storm, the truck was loaded with salt and while driving it suddenly went into limp mode and the OD light began flashing. Made it into a parking lot and after a few minutes it cleared itself. Nothing about the trans seemed to be an issue; upshifted and downshifted fine. We changed the two sensors located on top of the trans and it was fine for a couple of days. Took it out again after the truck had been sitting for a week and it immediately went into limp mode with the flashing OD light. It sat overnight, and the next day it was OK, but after driving a couple of miles same issue. We changed a third sensor on top of the rear diff, but no change. Nothing else seems related; hot or cold, air temp, recent fluid change, and everything else seems normal. Any suggestions?


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## Mnpowerstroke99 (Feb 12, 2010)

I'm not 100% sure but, I think when the OD light comes on it leaves a code on the computer.I think you have to take it to the dealer to have them read the codes for the transmisssion.A hand held code reader won't read them.


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## mrv8outboard (Dec 29, 2009)

There should be a code stored. Did the ABS light come on also? How about the speedometer? Was it working fine? Common issues I find is the rear wheel speed sensor as well as the range selector switch.


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## Flipper (Nov 1, 2001)

Go get it scanned. Even if the light stops flashing it has left a code. A lot of places will do it very cheap or free. It doesn't have to be a dealer. 

No sense in throwing parts at it until then. Usually problems with the transmission like you have described are sensor/wiring related. It would be hard to overheat the converter driving normally, even with a full load of material.

Usually to erase the codes and reset you have to clear them with a scanner or disconnect batteries (sometimes works). There is also a "training" I have learned from a Ford transmission tech. It involves drving 50mph with OD off for a few miles and then again with OD on. Not really sure how this works but I have done it a couple times after sensors went and I have trucks with 175,000 working miles with original trannies.


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## BlownAway (Oct 25, 2011)

Thanks for the replies. Here are the latest codes: PO750 & PO755; shift solenoid A and B failure, PO743; TCC system electrical failure, P1747; pressure control solenoid short circuit. There have been a few more codes prior, I just can't remember what they were. All seem to indicate a wiring or plug issue, but we have been unable to locate anything out of the ordinary. Pulled all plugs leading into trans and traced back wiring to no avail. No other symptoms go along with flashing od light/limp mode that are noticeable (ABS, speedo, tach, a/c, cruise control etc). Going to look for a complete wiring diagram, but if anyone knows where to look for the problem given these symptoms and codes it would be much appreciated.


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## coldcoffee (Jul 17, 2008)

My best advise is take it to a good wiring technician specialist, they tend to get a premium on their shop rate, but my experience is that they diagnose & repair much faster than any dealer or truck mechanic. Your problem probably lies somewhere between a computer, wiring harness or fuse block. I've replaced all the above in the past year on my 03, F350 Powerstroke. My last problem, in December was the fan clutch locked up which tore the wires & took out the fuse block. Same/ similar symptoms as you. My wire tech did in 3 days, what would typically take my diesel mechanic shop 3 weeks. It took 3 days because he got the truck on a Friday. He has better diagnostics, better resources & better, more efficient ways of resolving common issues (from poor engineering) so they don't happen again. If it turns out that you need a CFM, I found a guy in WI who rebuilds & will over night ship them the same day...saved me a lot of $$.


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## Plowtoy (Dec 15, 2001)

I know this is going to sound dumb, but check your trailer wiring plug (round 7) if the truck has one (i would assume it does being a 550). I have seen them back feed through the brake harness and cause the TCC to do crazy things, witch in turn could cause a OD flashing light? If their (round 7) not used in the winter they can corrode and cause issues. Its at least worth checking into


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## kimber750 (Sep 19, 2011)

BlownAway;1447507 said:


> Thanks for the replies. Here are the latest codes: PO750 & PO755; shift solenoid A and B failure, PO743; TCC system electrical failure, P1747; pressure control solenoid short circuit. There have been a few more codes prior, I just can't remember what they were. All seem to indicate a wiring or plug issue, but we have been unable to locate anything out of the ordinary. Pulled all plugs leading into trans and traced back wiring to no avail. No other symptoms go along with flashing od light/limp mode that are noticeable (ABS, speedo, tach, a/c, cruise control etc). Going to look for a complete wiring diagram, but if anyone knows where to look for the problem given these symptoms and codes it would be much appreciated.


4r100s are common to have harness and connector problems. Most ford dealers keep the repair kits in stock. If memory serves correct the repair kit is around $35 and you will need your vin # to get the correct kit.


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## BlownAway (Oct 25, 2011)

To make a long story short, after a lot of research (and some help from "JustAsk", the codes showed that the power to all the effected solenoids all came from one power source. Once I knew which plug at the transmission was for those solenoids, I tested each pin and found erratic voltage in one pin in that plug. A trace back of that wire harness found that it was being pinched between the body and frame (from the factory) and was frayed almost apart, but together just enough to flow some voltage. The condition was made worse when the truck was loaded. Simple fix, but took some time to diagnose and find. Thanks for the help all!


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## MickiRig1 (Dec 5, 2003)

That's great no big dollar repair. Good job!


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## wizardsr (Aug 8, 2006)

BlownAway;1448782 said:


> To make a long story short, after a lot of research (and some help from "JustAsk", the codes showed that the power to all the effected solenoids all came from one power source. Once I knew which plug at the transmission was for those solenoids, I tested each pin and found erratic voltage in one pin in that plug. A trace back of that wire harness found that it was being pinched between the body and frame (from the factory) and was frayed almost apart, but together just enough to flow some voltage. The condition was made worse when the truck was loaded. Simple fix, but took some time to diagnose and find. Thanks for the help all!


Where exactly is this pinched harness? I have an 01 and 2 03's with the 4r100 and I'd like to check them to make sure I don't encounter the same problem.


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## BlownAway (Oct 25, 2011)

Underneath the drivers side footwell where there is some heat sheald insulation glued to the bottom of it. The plug is on the passenger side of the trans, and the harness ran over the top of the trans to the drivers side frame, then forward under the drivers door/footwell and then up into the engine compartment. The section I found pinched was only about a foot long, but was impossible to free without loosening the body mount bolt which is located under a rubber plug under the floor mat. This no doubt occurred at the factory when they put the body onto the frame, because there is no way the harness could wiggle its way into where it was, even after 10 years.


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## coldcoffee (Jul 17, 2008)

Glad to hear you were able to find/ fix it yourself. My service tech said he deals w/ a lot of Ford wiring issues, due to poor design & poorly routed & fastened harnesses. I will never understand why there isn't more accountability when the flaws become so consistent & blatant. last time my truck was in for similar issues, they were working on a Hummer ( a show truck for Goodyear), waiting to go to a car show in Fl. The truck had caught on fire & they had it completely disassembled, replacing every harness...they had less than 2 weeks before the show. They get a lot of work from dealers (parts changers, as they call them) because so often, even they can't find the problems. That is one field w/ some major job security.


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