E40D failsafe mode
Fleet Mechanic
Joined: Aug 2001
Posts: 1,526
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From: Round Rock, TX
E40D failsafe mode
In conjunction with the dead speedo/odometer problem in my other recent post(92 Bronco 351W), the transmission shifts very hard and quite late. I have read that this is because the tranny goes into failsafe mode when it's not getting all of the sensor input that it needs. I have so far had the ABS sensor on the differential suggested to me as a culprit for the first problem. Does anybody have any input on what may have caused the tranny to go into failsafe mode, or about what the ramifications of driving the truck while in failsafe mode may be? Thanks in advance for any help.
Senior User
Joined: Feb 2002
Posts: 347
Likes: 0
From: ct
E40D failsafe mode
femm mode stands for failure effects managment mode. also known as fail safe mode. since your speedo doenst work and your in femm mode id say that the speed sensor in the top of the differential failed. now theres probably a reason for this. usually what happens is that an ear breaks off one of the clutches of the traction lok. that ear then gets meshed thru the gears and spider gears. as more parts break they all get grinded around in the rear as you drive. and what probably happened is that a piece of debris hit the sensor and killed it. ive also seen the teeth get marred on the abs ring that the sensor reads and this causes a erratic speedo. i wouldnt drive for too long like this because the epc pressure is at max and this causes banging gear shifts. take the cover off the rear end and inspect the internals. remove and inspect the sensor. its a magnet and any metal debris sloshing in the rear will stick to it. you may need a complete rear end overhaul but if your lucky the sensor just needs to be replaced.
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