About 5 months ago I purchased a 1994 Ford e350 7.3 IDI automatic cutaway 20 passenger short bus that had been converted to an RV. I should note that I live in Canada and this bus has lived it's life in intolerable Canadian weather.

On it's maiden voyage rom Toronto to Halifax (2500Km) the overdrive light had been flashing for half the trip. I now know how common this problem is and how often its been covered in forums. But, let me just tell you what I've done so far to see if it can give anyone enough insight to help me out of this mess...

The OD light was causing the transmission to act screwy and as anyone who's experienced this knows, it's very stressful, especially in a loud 7.3L.

But after having a few trusted mechanics asses it with codes they all assured me the motor and tranny were fine and that I just needed to replace a SPEED SENSOR. But, upon further inspection I discovered that before I could address that issue that there was MUCH more rust underneath this bus than I had perviously thought.

I ended up having to pay FORD $3000 just to get this thing to pass inspection. All cross-members had to be rebuilt, steps rebuilt, rockers, you name it. They actually did a pretty great job in that regard. I did all of this because the motor only has 250,000Km and I figured it was worth it if the truck was mechanically sound. Im a full time musician and hoped to use it for a couple years until I can afford something bigger. Then things went from bad to worse...

Ford replaced the speed sensor and two days after forking out $3000 in bodywork, the OD light started flashing again. I went back to FORD, they said "whoops we forget to clear the computer" or code, or something...

I told them while they're at it to replace the air filter, fuel filter and give it an oil change. That was another $300.

The very next day the OD light started flashing again. It's intermittent as usual.

I go back to FORD they look it over and soder some old wiring and say they can't find any other issue. The light is out, it should be good to go.

From there it's smooth sailing (and shifting) for about 300km and then BAM, OD light starts flashing again.

I decided to give up on FORD since I knew they would be no help and prayed it would just go away. A few days later the problem persists and now shifting is becoming a real problem.

I take it to a highly recommended transmission shop and the owner says he doesn't want to work on it because he doesn't think it's the transmission. He says it has to be electrical and recommended a Diesel Auto and Electric shop who specialize in that stuff.

I go there and we get codes 23 and 29. From what I understand (I don't know **** about mechanics if you didn't know by now) one code is related to the odometer/speedometer the other is related to a converter in the transmission I believe. The guys suggest that I replace the instrument cluster as they think this is the most likely problem. They did say that they couldn't guarantee it would fix the problem, so I knew this in advance.

All we can find is a used cluster from a junkyard obviously and $400 later they tell me to come pick up the bus, the light is out, it's ready to go. First thing I notice upon leaving is that the temp gauge in the "new" cluster doesn't work at all. 10 minutes into my drive home the OD light starts flashing. At this point im ready to have a nervous breakdown as I have a cross country tour starting in 2 weeks and no back up vehicle.

I brought it back to them this morning and they seemingly want to help me get to the bottom of this. They even suggested that maybe the replacement cluster is bad. But now, I have no faith that I will ever see the end of that OD light flashing at this point.

Can anyone offer any knowledgeable advice? I paid $4400 for the bus and have since spent $4000 on it and have not even been able to use it for one lousy trip. I feel like im in too deep to walk away but Im losing all hope. Some folks have told me that if it's electrical it's like like trying to find a needle in a hay stack to get to the real problem. That sounds pricey.

Thank you in advance for your time.

 

you need a few things.
patience,electrical cleaner,dialectic grease,patience,volt meter,code scanner and some more patience.
pull all the plugs and clean them thoroughly with electrical cleaner and apply dielectric grease.spending extra time with the large plug on the pass side of the trans.in the power distribution box under the hood,you'll see a diode and several relays.pull all those,and apply some dielectric grease as well.
plugs to clean and grease;
tps sensor plug located up on ip.
baro sensor up on firewall.
main ecm harness down under brake booster.
solenoid pack plug - main harness to trans on pass side.
mlps/range sensor/safety switch - sensor on drivers side.
vss.unplug and clean the plug,then pull the sensor from the rear axle and wipe it clean from normal R&P ware (may need to be replaced.code 29 should lead you here first,not the psom.)
even if anything appears to be ok,clean it anyway.these are all very old connections and might be corrosive.it sure isn't going to hurt anything lol.

once all electrical wires have been inspected and cleaned plugs,put the code scanner on and post your codes.
the code reader your looking for is called obd1 and they are sold for around 30 bucks at most auto stores when picking up the other things.
up by the drivers side hood hinge you'll see a couple wire connectors in plastic clips.unplug both and plug them into the code reader.press hold on the reader first,with key on engine off,now hold the throttle wide open on the ip.while holding this with your left hand (or just have someone hold their foot on the accelerator pedal to the floor) turn "hold" off and count the beeps/light flashes.post these for us here.
if you notice any blown fuses either in the truck or under the hood in the power dist box,be sure to post those as well.
also post anything obvious such as a tach inop or jumping/incorrectly reading speedo and insure brake lights function properly.if you find anything suspicious no matter how small it may seem with a wire/connector don't let it go unstated.

it's time to take matters in your own hands.we'll find these gremlins and expel them for good!

 

Ah HA, something I've had some experience with!

I have a 93 F350 and the flashing OD was the first problem I encountered. First I replaced the FIPL switch (easy to do even for someone with few technical skills--- you'll just need the correct tool to attach those torx screws).

Unfortunately, this did NOT solve my problem. It would keep the light off for a while until I got into town or stop and go traffic (when transmission was already warm) and I was went to point uphill somewhere. Every place I took it to tried to tell me I needed a new transmission or a transmission rebuild. I cried baloney since my truck didn't even have 100K miles on it yet!

I did a lot of reading (including on here) and I suspected it was in the wiring, but I did take it to one last transmission place for their evaluation at the recommendation of a very trusted shop. The guy in this little rinky-dink shop said straight away was the torque converter. I got some quotes from him on replacing just the torque converter, (and he since all I was planning on doing was towing with it he suggested I put in a shift kit at the same time).

I went home did some more web reading and took it back. Between what I read and what was confirmed by what he told me, the E4OD transmission uses the brake light circuit to unlock the torque converter. When you get torque converter lockup, transmission no longer is just fluid coupler. It becomes (most simply put) almost like a manual transmission with a clutch plate (not exactly, but for my brain that's the best way for me to think of it). If the torque converter didn't unlock as the truck slowed down, the engine would stall out much like a manual car would stall out if you didn't push in the clutch when you came to a stop. How the E4OD senses when to unlock is with an electrical signal when you touch your brake pedal.

However...

The signal required (I'm told) isn't necessarily enough to make the brake lights actually come on, but it is still related to the braking circuit and a flicker of fluctuation in the circuit is enough to unlock the converter. The guy at the transmission shop says it is very common for people who tow trailers (like me!) to have problems with the torque converter because of poor trailer wiring or dirty plug connectors.

When he replaced the torque converter (I upgraded) and put in the shift kit (which causes it to slam into gear sorta when it's unloaded) I had no problems...

Until...

I turned on my hazards one day while crawling uphill towing about 8k lbs. I noticed my rpms increased as soon as my hazards were on and dropped down when I turned my hazards off. I tested my theory a couple of times and it was confirmed each time. With this trailer and with the hazard lights on, the torque converter unlocks even though I'm not touching the brakes at all.

For the record, I'm using a wiring harness connector/adapter from U-haul that plugs straight into my wiring harness at the rear of the truck to run my trailer lights (I've since been told there is likely a separate stub installed from the factory somewhere just for trailer wiring-- still looking for that!).

Anyway, hope this long diatribe helps someone else with their trouble-shooting. As someone else mentioned, a dirty connector at the transmission of some other junction in the brake light circuit could indeed be causing enough of a fluctuation in the current to unlock the torque converter (and cause the OD light to flash) and it may not be enough to actually cause the lights to come or otherwise flicker on. Additional trailer wiring may also be the source of this electrical gremlin.

 

Thank you so much for taking the time to break this down for me. It seems like this would be the most cost effective way to start troubleshooting a flashing OD light. I am going to print out your instructions and have my mechanic do exactly this. Even if it doesn't solve the problem it's definitely worth a shot.
I will let you know how it works out.

 

Hey Spank, thanks. I guess you are saying that replacing the FIPL switch didn't help, but I couldn't tell from what you wrote exactly what you are suggesting as a fix. Are you suggesting to replace the torque convertor?

I should note that I am not doing any towing. The body of this 20ft passenger bus was converted to an RV, so aside from the fridge and the bed there shouldn't be any abnormal amount of weight that I am pulling. Just me and my dog (he weighs 10lbs) doing a lot of highway driving.

 

A secondary question I should probably ask at this point is how damaging is driving with the OD light on? I ask because most of my driving is highway miles and even with the OD light on it doesn't affect me too much once im cruising in high gear.

A couple people suggested that I just ignore the light and put up with it, since it's an intermittent problem.

 

it's of utmost importance.depending on what is wrong,you could be risking your multi thousand dollar transmission all for (possibly) a 30$ sensor,or even near free wire repair/cleaning.
whenever my OD flashes,i turn right around and head home and resolve the issue before i continue driving the truck again.
tip;
for code 29 (vss issue) if you decide to replace it,ask the auto parts counter person for a "ABS" sensor.this will allow them to find the part your looking for in their computer.- that's probably wrong of me to assume to rear axle in that rig of yours sports a tone ring.im not even sure if it's a sterling in it or not haha! well,if you see a wire connecting to a sensor in the top middle of the axle,then that's the abs/vss sensor that can fail (or just be dirty) and toss code 29.

 

I was just offering you my experience with no real recommendation other than to see if you can diagnose a bit further what's happening. For example, when you are going uphill and when the torque converter should be locked, try to accelerate without activating the kickdown and watch to see if the rpm's race up on the tach but the truck doesn't increase its speed in relation to the rpm increase. Then try that same test with the hazzards or turnsignals on.

An rpm increase could mean that the torque converter is slipping. And if it's doing it when the hazzards or turn signal is on, it could be because of a problem with the current that could be caused by dirty connectors, faulty sensor, or something else in the wires.

 

Hi! I'm new to this and this is my first diesel truck. I have a 94 7.3 idi non turbo with 245 000km that I've had for about a year now. No major problems but a few have started. One is a flashing OD light. It was on cruise control when it suddenly dropped out and the OD light was flashing. I pulled over, shut her down and restarted a few minutes later. This cleared it for the remainder of the 400km trip. So to me it seemed like an electrical fault with the transmission OD. It then started to do it more frequentley so I had it diagnoised at a good tranny shop in town. Code 29 showed up and indicated a speed sensor in the rear differential. One other bug I noted was the trailer brake module would light up as well as the brake light. I'm not towing anything so I don't use it. I thought I'd see about changing the sensor but trying to wiggle it out ended up breaking it. I figure I'll let the shop have a go at it as I don't want to screw this up anymore as I need it on another long trip in a couple of days. I did move the truck a bit and now the ABS light is on the panel. OD light is consitintley on and it shifts a bit harder. I'm noy using it until she's seen in the shop. They did say that it's a 60% chance that the sensor was the problem. It the follows up to wiring and the signal relay. If it receives a signal that isn't spot on ie a square wave as opposed to a saw wave the tranny computer doesn't know what to do and defaults to nurse home mode and the OD light comes on. Very worst case the computer can be fubared but that's rare. I'll update in another day or 2 with the result. Good luck to all those other flashing OD lights out there.
Cheers
Bill

 

WOW. It sounds like we are driving the exact same vehicle, with the same disease. Mine is a 94 7.3 e350 IDI, one difference is that I don't have cruise control. BUT, my dillema is almost identical. I can tell you I have spent $1200 so far including tax trying to fix this gremlin and have had no luck. The cheapest quickfix I have found is simply unhooking the battery and letting it sit 10 minutes, then hooking back up and driving off. It resets the computer which should kill that virus (flashing O/D) for another 4-500km.

I have replaced the speed sensor, TPS sensor and instrument cluster, and so far no luck. So, I would be interested to hear if your replacing the speed sensor has any effect on the problem. Most transmission guys have suggested it's electrical, but the longer this problem goes on, I can't help but worry that it might actually be the transmission.

Anyway, stay in touch! clemensfield@gmail.com