Flashing overdrive light & failed speedo

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Dougie Brown

Dougie Brown

Well-known member
Joined
Nov 16, 2007
Posts
960
Location
UK
An odd thing happened today.  After some very heavy work hauling us and the toad up mountains, we encountered road works which caused us to stop for about 10 minutes, three times.  I stupidly turned the engine off without letting it fast-idle for a while to allow tranny cooling (I know, I know) and after we started off from the second stop, I noticed the overdrive light was flashing on & off at the end of the great shift lever.  The switch still worked, as did all the gears.  I then noticed that the speedometer and odometer had failed.  At the third set of road works a few minutes later, I turned the engine off and restarted it, when everything appeared to reset.  The remaining 200 miles of the journey were uneventful.

Any ideas?  I'm guessing the transmission was overheating, but I can't see what the connection is to the speedo.

Dougie.
 
I don't think the tranny was overheating, or at least that was not the cause of the symptom. You would get a specific warning light for that, either Check Engine or a similar Check Trans light on the dash.  More likely just an electronic malfunction that was cleared by powering off and back on again, essentially re-booting the instrument. As to what actually caused the electronics to go woo-woo, that is anybody's guess. It's not something that mere mortals are to comprehend...
 
When I was still working we had an expression when symptoms would appear and then mysteriously be cured.  We called it F M for short.  Or as Cilo Greene would say in the F.C.C. approved version of his song Forgettin' Magic.
 
In my days of Naval aircraft maintenance, we often signed off aircrew gripes as CNC (could not confirm).  They hated that, by-the-way. :mad:
 
Molaker said:
In my days of Naval aircraft maintenance, we often signed off aircrew gripes as CNC (could not confirm).  They hated that, by-the-way. :mad:
Click to expand...

I can quite understand that.  ::)

Thanks guys.

Dougie.
 
Any informed ideas for this yet?  We've got another 340 miles tomorrow, and any info always helps prepare!

Dougi.e
 
It sounds as though you may have lost the speed sensor signal which would account for the flashing overdirive light and no speedo. It may be something as simple as resetting when you cycled the ignition to a more problematic problem as a connection from the sensor to the computer. Right now I would just watch it and see if it happens again. What chassis do you have Dougie? If you post your MH and chassis in your profile, it makes it easier to help in diagnosis.
 
Ok, Dougie, I see you are in the 37' Adventurer. I am not sure where the speed sensor is located on the Allison but it should be near the output of the tranny and will have 2 wires coming out.
 
I had the same happen to me earlier this summer. The problem is due to noise on the line from the speed sensor to the computer and they developed a new cable, however they no longer make the cable. The Ford dealer recommended replacing the sensor which I did and I haven't had the issue again.

kl
 
kentL said:
I had the same happen to me earlier this summer. The problem is due to noise on the line from the speed sensor to the computer and they developed a new cable, however they no longer make the cable. The Ford dealer recommended replacing the sensor which I did and I haven't had the issue again.

kl
Click to expand...

Sometimes just cleaning the connections to the speed sensor will take care of the problem.  It's mounted on the rear axle.
 
I had a Ford E4OD transmission on a 33' Coachmen that did the "light at the end of the shifter blinking" thing right before the transmission burnt up. I would check your transmission fluid and go easy on it until you can get it checked out. As Claude Akins would say, "That was a $3000 dollar transmission problem."

It may just be loose wires causing it to do that.
 
To clarify, the sensor I had replaced was the transmission output speed sensor on the Ford 4R100 tranny. The sensor is mounted on the left rear of the transmission. Hope this helps and you get yours running.

kl
 
The fault showed itself again today at first start-up, but also the MIL came on.  This gave me the opportunity to wield my new ODB-2 diagnostic tool, which shows a P0705 Transmission Range sensor Circuit (PRNDL) fault.  I called CoachNet who confirmed my thoughts that it would be safe to continue driving.  We've therefore continued to Winnemucca, NV where we're staying for a couple of nights, before heading to Carson City for four days and there San Francisco.

Assuming I believe the fault code, I obviously need to get the sensor replaced (or perhaps cleaned up?)  I don't wish to do it myself, so any suggestions of good/reasonably-priced techs in Carson City or en route to Frisco from here (I-80)?

Also rough cost of the sensor?

Dougie.
 
Molaker said:
In my days of Naval aircraft maintenance, we often signed off aircrew gripes as CNC (could not confirm).  They hated that, by-the-way. :mad:
Click to expand...

Eleven one "A" seven-ninety-nine! "could not duplicate gripe on deck".  :) couldn't resist!

The sensor is subject and vulnerable to moisture, salt, road grime etc. Sometimes the connector soaks and wicks puddle water into the pig tail. They're usually packed with dielectric grease by now but An RV..... Maybe no one's touched it yet.
 
I guess I'll have  the sensor taken off & cleaned, wiring checked for breaks, put back together, clear the fault codes, and suck it & see.

Dougie.
 
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