99.5 Blowing fuse #29 affect transmission?

[ryanlloyd80]

So my newly acquired 99.5 a4 2.8 quattro automatic transmission is blowing fuse number #29. The transmission in the car shifts ok sometimes but sometimes it's kind of all over the place. Lately it seems to not shift into 3,4,5. It will shift but goes into neutral & them boom shifts and jerks the car if you don't pay attention to the rpms. It downshifts fine. I already changed the fluid w/o any change in the shifting.

So my question is could a blown ecu fuse make a transmission shift like that or is the tranny just shot along with other issues? I do not want to spend time figuring out the cause of the blown fuse if the trans is done.

[walky_talky20]

Absolutely, yes.

Fuse #29 powers important engine sensors like your Mass AirFlow sensor (MAF). That is used by the Engine Control Unit (ECU) to calculate engine load, among other things. With the fuse blown, the engine just runs on a very rich map which works ok. But the ECU is also responsible for communicating engine load values to the Transmission Control Unit (TCU). That way it knows when to shift. Being a fully electronically controlled transmission, as you can imagine this is somewhat important. Without good values from the MAF, it is unable to do this.

I can't say for sure that all your shifting issues are *definitely* caused by your blown fuse, but I would never expect the transmission to shift perfectly in that condition either. You can check the TCU for codes. If you see slip codes (incorrect gear ratio, etc.) or solenoid performance faults, then you have troubles. Otherwise it could just be a control issue due to your missing sensor data.

[ryanlloyd80]

Thanks for the great response! That's what I was thinking but I assumed the car wouldn't run with fuse blown & it did.

As for the tranny. I don't have a vagcom yet which is what I think you need to check trans codes but i wouldn't say it slips. Only other car I had that slipped was an accord & it was like riding clutch when it shifted. My a4 just cones out if gear & then shifts. It's like it's in neutral for 3-4 secs before it shifts.

Forgot to mention. It throws every o2 sensor code & secondary air code. I replace the fuse they turn off until I turn the key back in & they're back. The fuse blows on startup after it's warmed up