Who's your guy in queens?I recommend Mspec in middle village

I would also clean your MAF sensor. My X has a history of Trans Failsafe Prog messages, which sometimes just put the tranny in limp mode, and sometimes actually kills the engine. It's lots of fun to try and steer an X5, with impending traffic furniture coming up or another car, without a power steering pump!

Anyways, after years with the issue, and help from this very board, I've determined that 100% of the time its a dirty MAF sensor, which is then interpreted by the ECU to trigger the TRANS FAILSAFE PROG dash message, and sometimes even shut the engine down. I've always pictured a German engineer on the team saying (in your best German accent), "Hey, let's prrrograam ze ECU to shaat down ze engine ven ze zimple leetle air flow zensor is just duurty". haha.. (My wife is German, so I can tease a bit, no?).

MAF stands for Mass Air Flow, and its a 4" diameter plastic tube with two metal cross hairs inside, plus a electrical connector on the outside of the tube. Its mounted in between the air filter box (air intake for the car), and the engine's air intake snout, all inline / part of the air intake plastic plenum (piping/tube). Its super easy to remove and replace. The metal cross hairs sense moisture levels, temp and other things from the air traveling into the engine, and the ECU monitors this and adjusts the engine's fuel, air, and spark advance to compensate for changing environmental conditions. The metal on the cross hairs is some type of rare earth mineral... so.. it's therefore ultra sensitive to getting dirty and altering the readings. Most mechanics will just replace them (but they're fairly expensive), or, you can just try cleaning the cross hairs.

I suggest pulling the MAF sensor (out of the car, don't just disconnect some), and heavily spray it with Hexane. You can buy Hexane at any auto parts store. It may even say, "MAF Sensor Cleaner" on it. Don't touch the cross hairs, and don't use anything else to clean them. Don't just spray it once. I tried that, and it doesn't really clean it enough. You basically have to expend 1/2 of a can of Hexane spray on it. It will be dripping heavily onto the ground. Keep spraying off and on. Reinstall.

All 7 times I've had the TRANS FAILSAFE issue, replacing or cleaning the MAF immediately resolved the problem, and it doesn't come back for 30k to 40k miles.

It might be what the guys are saying too. (I'm keeping this thread for that info. Great, detailed auto trans information I did not know!). I'm only saying, try the MAF sensor cleaning too, just in case, and it will only cost you $7.95. If the cleaning doesn't work, I'd also consider replacing the MAF. They don't always clean up perfectly.

I think I just ran into this: I got the transmission light on the dashboard (cogwheel with exclamation sign in its center) the other night and a service engine soon light too. I read the codes off the ECU and got only one code: "Air Mass Sensor".

So, I overlooked that code because I did not think an "air" sensor could affect the transmission, so I thought for sure the transmission was messed up. The car was now shifting very rough, especially when it would downshift as I approached a traffic light or any kind of stop...

So, I took it to a shop that specializes on transmissions, and left it with them for the day. They called me later to tell me that the transmission looks fine and that they are 99.999% sure it is the "Air Mass Sensor" code that is causing the computer to make the transmission shift roughly, because when they cleared the "Air Mass Sensor" fault, the car shifted just fine.

So... I am gonna go clean the MAF sensor as recommended here and see what happens...

The transmission shop was also able to read other codes which my ECU reader did not show, they are:

- (8) Air Mass Sensor Signal
- (149) Can Wheel Speed Signal
- (146) Can Engine Intervention Interface
- (33) Wheel Speed Sensor Front Left Circuit

I changed my alternator and it seems to work and drive even better then before , it was a voltage issue , no Air Mass Sensor code on mine... Hope that works for you as I am sure it is cheaper then the Alt...

Ok. Cleaning the MAF did not solve it. I spent nearly half the can on it too and left it drying over night...

So, I am buying a new MAF... It gets here tomorrow. We'll see...

Good Luck and keep us posted on the out come as it may help others....

For clarification, the wires on the sensor itself (where the electrical connection goes) are the wires that need to be cleaned There are two locations where they are wires on that sensor. I remove the sensor from the tube to clean it. And, I have cleaned MAF sensors that were bad and ended up replacing the MAF because the cleaning was not successful.

I've cleaned and replaced the MAF many times, there were symptoms that became extremely obvious that never resulted in any warning light. Symptoms of a problem with the MAF are most often a significant loss of engine performance and the engine roars but won't rev or won't rev normally.

As has been suggested, I would use the cluster test to monitor the alternator output in realtime as something else to that is easy to troubleshoot.

Woe woe woe, you may have a bad wheel speed sensor since this was one of the original codes. Another area that could cause the trans failsafe is the ABS/DSC module. I just had this problem with my X5 where it was the ABS/DSC module causing the fault. My vehicle had codes for 2 wheel speed sensors. Highly unlikely both would be defective. So I used the live data on my scanner to see which wheel sensors were not reading. Switched the wheel speed sensors on the vehicle and no change in operation observed thus confirming a fault in the ABS/DSC control unit.

:iagree: I wouldn't chase the cause with new parts. Keep troubleshooting. It may or may not be the MAF, battery, alternator, wheel sensor etc.

Thanks folks. I had already ordered the MAF and it got here this morning. I installed it and the the transmission light went away and the car shifts smoothly now. So, I cleared the MAF code using my cheap (bavauto SR 300-16) ECU code scanner.

However, after driving the X5 about 1 mile, I got the "Service Engine Soon" light, and reading the ECU yielded:

- O2 Sensor adaptation limit (1-3)
- O2 Sensor adaptation limit (4-6)

So, I drove it about 5 miles more and then the DSC, BRAKE and ABS lights came on.

I had replaced all 4 of the speed sensors about 5 months back, so I doubt it is the sensors.

How could I troubleshoot these two problems (O2 and the speed sensors)?