Ford: ford truck problems, vent hose, code tester

Question
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Followup To
Question -
yes first thank you for your time.  I have a 1994 f-150 4wd truck. It has the 302 in it.  I went off road in the mud  about a week and half ago.  I got stuck and had to be pulled out.  My truck sat in muddy water for almost an hour up to the back bumper.  After i got towed out it started right up. about three days later i was going down the highway doing about 70mph for a period of 20 min.  My check engine light came on. So i checked the fluids and everything was fine. The light went off.  It comes on now when ever i travel at high sppeds (65-75mph) for periods of 20 or more minutes.  What causes this??  Also since my truck was sitting in the water for that long i was told to repack the bearings in the front.  I just got my brakes done a week earlier.  I went to auto zone and the guy told me on my truck i don't have to repack the bearings that it gets lub from the back axle fluid.  Is this true? Also I was told there is a vent hose leading from the rear axle up into nothing to vent the hot air build up. I was told if water went in to it I would have to drain the back axle fluids.  What do I have to really do to the truck to make sure it is ok.  is sitting in water for that long going to affect my new brakes?  sorry for all the questions.  thank you so very much.
robert
Answer -
Robert what i would do first is go back to auto zone and have them ck for codes let me know what you come up with .We'll start there .


ragu I went to auto zone and they can't test it because it is a 1994.  Only trucks 96 and newer have the computer system in it to check the codes.  What about the water to the back end???
Thanks Robert.

Answer
the water in the rear end would not turn on the ck eng. light it wouldn't even turn the abs light but to be safe i would replace the rear end fluid .you might have to go to the dealer or a severce shop just to pull the older codes.lets do this you can also get a code tester from auto zone that would just flash the ck eng light and you can count the codes. let me know