Hi, I have been having troubles with this issue now intermittent for some time now. When the OD light blinks, the tranny shifts hard. Last night I changed the rear differential fluids and replaced the speed sensor while I was back there hoping that would fix the issue. Took it for a drive last night and the OD light is still blinking. Intermittently. Sometimes when I go thru the gears it won't blink, then other times it will and then it shifts hard. Error code 67 came up when I did the scan a few days ago, park/neutral circuit fault. I went and picked up that sensor last night, but I don't want to keep throwing parts at it if it doesn't need it. Any advise?

 

the flashing light often times will cause the firm shifting.that's the result of the control unit sending high line pressure.
you need the code(s) to help you troubleshoot.what made you suspect the VSS/vehicle speed sensor? was/is the speedometer erratic or non functional? or did you forget to mention you got the 27 or 29 trouble code?

Pete,(besides getting the codes) this is a good place for you to start.
E40D: The Importance Of A Clean Trans Harness.

 

Yes, there was another code, 23, 10, 29 and 67 but when I did the scan the other day, it was only 23 and 67

 

for 23,did you hold WOT during the KOEO scan?
for 67,since the flashing light is intermittent,i would first try cleaning the MLPS plug and pins on the sensor,before replacing it.

 

I find that whenever I turn the OD off when I'm going up a hill or have a load on the back then the light will start blinking shortly thereafter. Maybe it's coincidence or is it related?

 

Check your third brake light... if it's burned out your E4OD is going to have similar issues to what you're experiencing.

 

Wow, third brake light not working can cause this? I have to ask how is that possible? I don't want to be scepticle, I'm not a mechanic by any means, but how does the third brake light affect the transmission?

 

It was made possible by Ford engineers -- who else?

There's a switch on your brake pedal that lights up your brake lights when you hit the brakes. Through your third brake light, that switch is also connected to the transmission; the torque converter is supposed to unlock when you step on the brake (in addition to disengaging the cruise control).

When your third brake light bulb burns out, strange things start to happen involving the transmission. A couple of these symptoms are the torque converter randomly locking/unlocking, and a flashing O/D light. I had very similar symptoms to what you are describing on my 94 -- until I replaced the bulb.

It's a $5 fix and an easy way to eliminate a possible cause.

 

You're talking about the third brake light, the one at the back cab? Above the rear window?

 

Yep, the same.

 

i don't believe the 3rd brake light was introduced until the 1994 model year.
pre '94's simply had the courtesy lights back there.one less potential E40D issue for us pre '94er's lol.

code 67 (MLPS issue) would be my focal point.i would carry the scan tool,do whatever it took (hit the cancel switch while climbing a hill under load) to trigger a/the fault code.pull over and perform the scan to see what else may be intermittent and not storing,if anything.
the code scanner is your friend.you want 11 = system pass.codes 23 (while holding WOT durring scan) nor 67 can be present.if you don't make these go bye,bye, (not by simply clearing the codes lol.actually repairing the issues,either via replacement sensors/adjusted and or cleaned contacts etc.) then the trans will never operate correctly.

 

I have cleaned all the wiring harness connections and checked for fraying wires, replaced the speed sensor in the differential and changed the fluid.
The OD light is still blinking.
Plugging in the scan tool, the following codes come up.
13
23
10
29

 

13?

23 = Throttle sensor out of range or throttle set too high
did you hold WOT during the scan? (why don't you answer this question?)
what's your idle set at? when was the sensor last replaced? what is the idle and wot settings?

10?

29 = Vehicle Speed Sensor problem
how is the speedometer needle working?

67 = Park/Neutral circuit fault
Transmission Manual Lever Position (MLP) sensor circuit
(M) Intermittent Park Neutral Position (PNP) sensor fault

this one is still intermittent? did you do anything to the sensor (adjustment/read it's values) or replace/clean it's connector?

 

I do not know what the "wot" is? I have a ford obd1 tester. It only has three buttons on it, ("memory, on/off, test/hold")
I have cleaned all the connections with contact cleaner
I am not sure what my idle is set at, where would I do that?
My speedometer is reading correctly, or appears to. I have a friend of mine working on the truck and he is going to replace the rpm sensor today. It seems I am now just throwing parts at this thing.

 

WOT is wide open throttle. Diesels don't have throttle plates, but the term means hold the accelerator pedal to the floor.