Trans Failsafe and code P1748

[x5drew]

I have a 2001 4.4 X5 with 100,480 miles.
The trans failsafe turning on and the service light.
I read codes with my code reader and got P1748 code i looked it up and found bmw code p1748 Transmission control module self test .

Truck went into Trans Failsafe when driving 60 mph in lite rain everything ran great untill it went into Trans Failsafe. I turn car off and restart and service engine light & trans failsafe turned off and everything runs great then i drive less than one mile and it goes back to trans failsafe mode service light is on and i get P1748 code. I reset it and it goes back to Transfailsafe everytime i reset it after less than a mile i drive.

I also try to turn key on ten seconds turn key off ten seconds then start car it clears service light Trans Failsafe message turn off runs great about a mile the it goes back to trans failsafe mode and service lite turns on I check code and get P1748.

Trans works great when Trans Failsafe mode is off but it wont stay off.
I dont think i have bad a transmission.

Work that i did in last few weeks.
I installed new Valve Cover Gaskets, New Plugs, New Plug Boots, New Coils, new Oil and Filter, new Air Valve, two new Cats and Oxygen Sensors,
Everything works car ran great no codes no service lights for two weeks untill three days ago I had to installed new speed sensor rear passenger side three days ago to clear up the dsc three dash lights that turned on on the dash the new speed sensor turned all three DCS lights off on the dash.

Now trans failsafe problem and code P1748 ?
Any Ideas?

Thanks x5drew

[Zoomie]

How is your battery?

[wallyx5]

Originally Posted by Zoomie

How is your battery?

Check your battery, that could be your problem. Let's hope it is.

[x5drew]

I checked batterywith a meter yesterday check out good on meter from under hood today i will look it
over (terminals wires water).
I installed a new battery from autozone last spring. i was thinking it might be alternator. The battery holds charge car starts like battery is full power meter shows alternator is good. So im not shure about alternator being bad.

When i start car interior lights seem to dim down for a second or two then normal then dims then stays normal or maybee i dont notice them anymore because they turn out automatc after car is running.

Car headlights and dash light look good normal no dimming at night stay bright
so i think alternator is good is there a regulator maybee ?

I am looking into seeing if ther is water on harness in e box under hood i read water gets in in there and needs to be dryed and cleaned up i post back after i look at battery and e box.

Do alternators act up before going out or do they just quit working all at one time ? or is there a regulator?that might be going bad.
Thanks Drew

[Weasel]

Could be a voltage regulator, or maybe even diode bridge problem if it is a voltage issue from the alternator.... To check the diodes just use your meter to read AC voltage at the terminals as they are what turns the AC output of the alternator into DC voltage for the car to use. I think the most AC voltage you should see is under a volt. (memory pending)

But I don't think that is the problem givin the conditions. I would think your best bet would be to have a diagnosis done with the BMW GT1 equipment, either at the dealer or any such equipped BMW specialized independent shop. There is so much more information that may be there that you aren't seeing with the regular scan tool. BMW has its own proprietary fault codes and attached to all faults read through the GT1 are guided test plans to give you any additional information needed for diagnosis.

You may need a new transmission control module, or it could be something else. Best bet is to just have the proper diagnosis done first. Good luck!

[Bismark]

P1748 IS AN OBD II CODE. THIS CODE INDICATES THE PRESENCE OF AN ERROR CODE IN THE PCM. TRY TO RETRIEVE THE EQUIVALENT BMW ERROR CODE. IF U DON'T GET THE MANUFACTURER CODE IT'S GOING TO BE DIIFICULT TO SOLVE UR PROBLEM. CHECK THAT SPEED SENSOR AGAIN. IS IT OE??? MAY BE IT' DEFECTIVE. GOOD LUCK.

[x5drew]

Took a look at transmission wires under car the plug infront of trans pan was the problem i un pluged the wire harness the big round one you have to unscrew i unscrewed it and alot of dirt / dust came out like dirt from dirty water drying up cleaned it put back togeather started car no trans failsafe i clear light with my code scanner drove abot sixty miles so far everythin works great.

The code said transmission control module self test so i thought it must have a self test that not passing it showing one sensor code for self test and other things check out so i thought maybee a connector is dirty or loose or got oil on it from the oil leak before i changed valve cover gaskets sometimes codes are just a start to see where to look for what is causing code to show not just a part to look for.

Everything seems well with it so far i want to test it in the rain yet to make shure. It was raining when problem started.

Thanks for replys this newsgroup and its users are great.
x5drew

[Bismark]

well done.

[Kuddel]

It may be one of your Module, you have to find out which on, behind your Driver side front headlight is a Module, which in my case was the on failed, and I had the same
codes, there are total of three Module, the other two 1 is on the Transmission itself and the third location I due not remember, anyway I just disconnected the Module and Trans Faile Mode was gone, so this was the Module which needed work, You can take it out by loosen 6 screws.

Just go and Check Modulemaster in Moscow,IDAHO there website you how to take the unit out and send in for Repair if this is your problem, it sure was mine Total cost
to me $325- and 5 years warranty. Everything fine now.
2000 X5 4.4i only 250 k on it one owner. Dealer quote $1795

Kuddel