p0720 output speed sensor error..

[RRPhil]

Hmmm, that sounds more serious than just a speed sensor problem. Does the transmission behave itself better when cold and get worse as it warms up?

Phil

[turquise1]

Could be, before it came to this point (p 0720 error and TRANS FAIL SAFE), my car actually would shift not as smooth after the engine heat up (I mean heat up after at least half hour of stop-go driving, but not overheat) but I always blamed other parts (like emission for that).

Oz

[RRPhil]

The reason I ask is that I often get 5HP24s to repair where the transmission behaves normally after starting from cold but then after around 20 minutes (which is how long it takes for the transmission fluid to get up to temperature) the transmission failsafe message appears & the transmission goes into limp-home mode (4th gear + open converter). On cooling down again, normal operation is restored.

This is invariably linked to a seal leakage problem. When the fluid is cold and viscous the leakage is small enough that the pump flow is sufficient to maintain pressure on the particular clutch. Once the fluid warms up and the leakage increases the pump cannot maintain pressure and the clutch slips. The ECU detects the slippage via the two speed sensors and drops into failsafe.

Similarly, if the transmission fails to engage either Reverse (C & F clutch) or Drive (A clutch) at tickover, but then slams the clutch(es) on when the engine revs are increased, this could also indicate that the additional pump flow produced by increasing the engine speed was overcoming a seal leakage problem.

Phil

[turquise1]

Well my mechanic had bad news for me. He said the sensors were ok and the torque converter was gone, so my transmission would need rebuilding.
They are asking for $3k for everything, I guess it's a good deal, I will probably go for it..

Thanks again for all the help..

Ozzie

[BmwBrian]

my dsc module crapped out the other day but it causing my cluster gauges to go bananas... ie: no rpm or speedo and temp gauge redlining and returning to normal...
when i disconnected the dsc module the cluster returns to normal.
rpm comes back and speedo and normal temp.

i assumed it was the module and sent it out the shop says in unrepairable after feeding me a bunch of lies on how they were working on it then tell me under a scope 2 days later its damaged...thats a whole dif story im sending the unit for a second opinion...

my question to you is you describe my tranny symtoms to a t and i prepared for this day...i changed the filter and fluid only in the pan and it bought me 20k im currently at 148k miles.

it seems like its warming up then the a disc slips could this be anything in junction with the dsc module? is the tranny module on the same circuit and could it be the cause of the dsc unit shorting my cluster?

im wondering if its just the tranny since i know the tranny has been crapping.
but could it be the dsc unit too and at the same moment the tranny dies?

it is a bmw i guess lol

but i wonder if my abs module is bad at all is the tranny ecu on the same canbus as abs module?

any help is greatly appreciated!

[BmwBrian]

PRO!

Originally Posted by RRPhil

The reason I ask is that I often get 5HP24s to repair where the transmission behaves normally after starting from cold but then after around 20 minutes (which is how long it takes for the transmission fluid to get up to temperature) the transmission failsafe message appears & the transmission goes into limp-home mode (4th gear + open converter). On cooling down again, normal operation is restored.

This is invariably linked to a seal leakage problem. When the fluid is cold and viscous the leakage is small enough that the pump flow is sufficient to maintain pressure on the particular clutch. Once the fluid warms up and the leakage increases the pump cannot maintain pressure and the clutch slips. The ECU detects the slippage via the two speed sensors and drops into failsafe.

Similarly, if the transmission fails to engage either Reverse (C & F clutch) or Drive (A clutch) at tickover, but then slams the clutch(es) on when the engine revs are increased, this could also indicate that the additional pump flow produced by increasing the engine speed was overcoming a seal leakage problem.

Phil