4WD / Speedo problem

[Tim O]

Hi guys,



Here's my problem: 2002 4x4.



When it is below ~50F, when I start up in the morning, both the 4WD Hi and Lo lamps are lit, and the speedo reads at half speed. This lasts for ~5 minutes until the truck is warmed up. This is quite repeatable and happens every cold morning.



My thought is it is an electrical problem with the module getting inputs that makes it think the transfer case is in both hi and lo positions at the same time. I imagine when in 4WD Lo, the drivetrain ratios case the wheels to turn about 1/2 speed so the speedo reads 1/2 speed when it thinks it is in Lo.



Anyone have a link to the system skematic so I can trace the wiring and see where I may have a short or open when the vehicle is cold? If the inputs pin out then it is the module. Would prefer to spend some time troubleshooting than swapping the module to start.



Thanks for the help!!!!

 

[Todd Z]

I don't think the speedo is corrected by the module but i can be wrong....



I don't know where you live, But maybe some one can let you swap out a 4x4 module and try that first..



Todd Z

 

[Don Donaldson]

That is very interesting,

I know on the 2wd models the vehicle speed signal is generated by the pcm via the OSS (transmission output shaft speed sensor). The sensor is a "hall effect" type which means it generates a zero crossing sine wave. This is processed by the PCM and converted to a square wave where 5000 pulses equals one mile traveled. I would assume that this would be the same for the 4x4 model except instead of the a sensor in the tail shaft of the transmission it uses a sensor in the transfer case. Also in the two wheel drive the speed signal is distributed in parallel to all the devices that need it, such as the GEM, Cruse control, ect.(just like x-mass tree lights) I do not believe that the 4x4 control module generates the signal but I could be wrong.



This product will take any abs or transmission sensor signal and process it to the square wave the truck wants. I used it over oem because for the cost of programing and purchasing the ford modules this was far cheaper and I could easily change it for any new tires and other mods.

I run mine off the rear abs signal.

-Don D.



Just give them a call and tell them your problem... they where very helpful and friendly.