Shift Inhibit

Shift Inhibit Table

The Shift Inhibit table allows the tuner to prevent gear shifts which are either unwanted and/or dangerous. track.

Shift Inhibit will only block shifts if the functionality is enabled and the specific shift is listed on the left axis of the Shift Inhibit Table.

Note that if enabled and configured for it, the shift inhibit can block any shift request except the Spool-up Gear shifts.

This is a special table which behaves differently to normal tables. The behaviour is described below. The left axis is fixed to the Shift Inhibit Axis in order to achieve what is needed.

Here is an example Shift Inhibit table that might be used in a drag race application.

Because only the shifts from 1 -> 2, 2 -> 3 and 3 -> 4 are listed in this example, only those shifts can be inhibited. A shift from 4 -> 5 won't be inhibited, nor will a shift from 3 -> 2.
Note that the table can contain any combination of up and/or down shifts. If the shift is listed in the axis, it is checked for shift inhibit. If not, the shift inhibit won't apply.

Up shifts require that the Shift Point Variable Value is greater than or equal to the value in the table for the relevant shift. (e.g. shifting 1 -> 2 can only happen if the Race Time channel is >= 1.2 seconds)

Down shifts require that the Shift Point Variable Value is less than or equal to the value in the table for the relevant shift.

Note that for the purpose of shift inhibits, a shift request which skips gears will check all intermediate gear changes. e.g. a shift from 2nd to 4th will check the shift inhibit table for 2 -> 3 and then for 3 -> 4. If the 2 -> 3 shift is inhibited, no shift will occur. Otherwise, if the 3→4 shift is inhibited, a shift from 2→3 will occur instead of the requested shift to 4th.

Shift Inhibit Status Channel

The Transmission Control Shift Inhibit Status channel can be used to determine the status of the last Shift Inhibit check.

Text	Value in Log	Meaning
No Request	0	No shift requests have been checked since the ECU powered up.
Allowed	1	The last shift request was allowed.
Not All: skip disabled	11	The shift request wanted to skip gears, but Allow Gear Skip is disabled. Still shifted one gear.
Not All: Down-shift Over-Rev	12	A down-shift was performed, but not as many gears as requested. Down-shift Over-rev protection was the limiting factor.
Not All: Shift Inhibit	13	A shift was performed, but not as many gears as requested. The Shift Inhibit table was the limiting factor.
Blocked All: Down-shift Over-Rev	22	No shift occurred. Down-shift Over-rev protection was the limiting factor.
Blocked All: Shift Inhibit	23	No shift occurred. The Shift Inhibit table was the limiting factor.
Blocked: Gear Doesn't Exist	24	The gear doesn't exist. e.g. If the driver selects Reverse on a transmission which doesn't have reverse.

Recommendations

If you want to prevent the engine over-revving on down shift, it is simpler to enable the Block Down-shift Over-Rev functionality.

Drag race application can use Race Time as the Shift Inhibit Variable to prevent automatic gear shift requests caused by wheel spin.