Tii Reverse Switch Thread

[JustJeff]

Originally Posted by Pete_89T2

On the S5 T2, that particular switch serves 2 functions - senses shifts to reverse for the B/U lights and whether or not you're in 5th gear. The ECU uses the latter function, so I'm not sure replacing it with a plug is a viable option if you run a stock ECU.

My understanding on the 5th gear switch is that it's used for either emissions or fuel economy..or both. I can't remember ATM. I've been told this by some credible sources, but didn't research to find out on my own.

I drove my turbo with no switch at all for several years with no adverse effects. I never threw any CELs. I annoyed the shit out of quite a few drivers as they had no warning I was about to back out of a parking space...but..."eh".

With my rebuild I took the time to splice some wiring from the prongs that are left on my switch to the USDM OEM wiring....well for the reverse lights, not the 5th gear switch.

[vrracing]

We did it when we were rebuilding the engine so it was out and convenient. If it wasn't a PitA, I would have had the kid pull it out and just taken it to the fastener store and have them match it up.

I dont remember what we did with the 5th gear switch wires. It's never affected the car.

The engine has two mounts - one on either side - so I suspect by disconnecting the mid pipe and the tranny bracket (we had a custom one made since this is a Tii in a vert) the tranny will angle down enough so we can get at it.

[Pete_89T2]

Originally Posted by vrracing

We did it when we were rebuilding the engine so it was out and convenient. If it wasn't a PitA, I would have had the kid pull it out and just taken it to the fastener store and have them match it up.

I dont remember what we did with the 5th gear switch wires. It's never affected the car.

The engine has two mounts - one on either side - so I suspect by disconnecting the mid pipe and the tranny bracket (we had a custom one made since this is a Tii in a vert) the tranny will angle down enough so we can get at it.

I was thinking about dropping the tranny mount too, but I don't think that would result in enough space either. There's not much clearance between the firewall & the engine block for it to pivot back, so the block will probably hit firewall before there's enough clearance at the tranny to get to the switch.

From what I can gather from the FSM, the 5th gear switch is used in part of the ECU's decision logic for operating the fuel/air maps in closed loop mode. If you drive your FC like most of us do, you probably won't notice any difference. The majority of the time, it will run open loop; closed loop running only happens under "granny driving" conditions - low load MAPs and a narrow range of RPMs, below where the secondary FIs kick in.