99 740il trans fail safe

[heifetz17]

Hey guys, I just picked up a 1999 740il as a project car and I have some recurring trans issues on it, and trying to decide if it's worth throwing some relatively cheap parts at it before replacing or rebuilding the trans.

The car has 173k miles on it and when I first got it, it had codes P1743 and P0743. I cleared those and they haven't come back.

Now when I drive the car it's runs/drives/shifts great until it warms up and will periodically go into trans fail safe mode and throw P0720. I do know about the A-clutch drum common issue, but I also understand that it would be a mechanical failure and would not be an intermittent issue like this one.

The speedometer does not work, and I have an ABS light (both undiagnosed as of yet), if that might be related in any way. If I clear the code (P0720) the car will drive normally for a bit before eventually going back into fail safe and throwing the code again.

Given the prior codes for TCC, inop speedo, and intermittent nature of P0720 would it be worth the relatively low cost to drop the pan, change the fluid, and replace the input and output speed sensors before condemning the whole trans?

[Mayorchuck]

That code is usually due to either low voltage from a weak battery or one of the clutches has failed. Low voltage can causes one of the solenoids to fail. Since you have an ABS/sensor issue, I would address it first to make sure it's not causing the issue. The speedo works off the rear drivers side wheel speed sensor.

[Fanatech]

I would suspect the torque converter and or worn clutches in the trans. Can hold the pressure until warm and then the car senses slip outside parameter and throws failsafe and if really bad will put it in trans limp mode stuck in 3rd I think. Low voltage on these cars can cause havoc but the 5hp24 is far from a stout transmission.

[Timm]

Does the gearbox actually go into Fail-Safe Prog? If it does you will be stuck in 4th gear until switched OFF and back ON again. But first, fix your ABS and speedo issue which is probably a wheel sensor


More info here:

[goinstrong]

I had a 1995 that would act similarly to yours. May your "fix" be as simple as mine which was a new battery and chasing down a battery power drain when it sat overnight. Never had another issue with the transmission. Hope this helps!


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