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Post Info TOPIC: ZX-14 gear select and the TRE


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ZX-14 gear select and the TRE

Some one who has a TRE installed on their ZX-14 asked if I knew how they could switch back and forth between normal mode and TRE mode. For those of you unfamiliar with the TRE it plugs into the wire harness between the ecu and the gear selector switch. It fakes out the ECU into thinking it is a different gear than it really is. There are several reason someone might want to do this; eliminate a top speed restriction, or a low gear power limitation.

I am not an expert on the ZX-14 gear system but I know enough that with a little help we can figure out exactly what gear the TRE is trying to make the ECU think it is in and how to design something that will bypass or replace the TRE.

To start with here is a schematic approximation of the ZX-14 gear circuit and TRE. The factory manual schematic inset is actually kind of misleading.

The gear selector creates a voltage that varies with the selected gear by creating a voltage divider circuit with Recu and a selected resistor in the gear selector. Before we can design a bypass we need to know the resistance values of Recu, and R1 thru R7 in the gear selector switch. Once we know what the normal operating values are we can figure out what the TRE is doing.

Step 1:
Refering to the diagram above disconnect the gear selector plug (Gear) from the TRE-G plug.
Using an ohm meter measure the resistance between Black wire and the Green/Red wire of the Gear plug in each gear and neutral and post it here.

Step 2: figuring out the value of Recu; We can't measure its resistance but we can calculate it by knowing either its current to ground or voltage across a known resistance. So we to do one of the following...

Option A
Disconnect the TRE-E plug from the ECU-G plug. Set your meter for DC mA mode and measure across the Green/Red wire and the Black/Yellow wire of the ECU-G plug with the bike key turned on.

Option B
Disconnect the TRE-E plug from the ECU-G plug. Place a 1K ohm resistor between the terminals of the Green/ Red wire and the Black/Yellow wire of the ECU-G plug. With the bike key turned on measure the voltage across the resistor.

Once the results of these first two steps are posted we can move on to the TRE.


Veteran Member

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Posts: 80

well, although it's not a zx14, my sv1000s has a similar setup

the resistance values are
R1 - 567R
R2 - 827R
R3 - 1k5
R4 - 2k7
R5 - 6k8
R6 - 15k
R7 - does not exist
Recu - 1k

given the similarities between the ecus on the kawa and suz.,
there's a good chance that the timing retard operation is also

generally the TREs for the suzis place a 15k resistor between
the pin on the ECU and earth, to simulate 6th gear all the time.
Works ok except at cold start up, when it's preferable to not
eliminate the retardation.

so the smarter TREs detect neutral ... when earth appears on
the neutral wire (Lg) the TRE disables and a cold bike can be
started in neutral with no problems

the cct is simply an NPN transistor, collector connects via a 15k
resistor to Recu, emitter goes to earth, and the base connects
to the neutral wire via a 47k resistor.

when the bike is in gear, the base gets biased by the voltage
that appears on the neutral wire, coming from the neutral idiot

when the bike's in neutral, the base is pulled low, the transistor
is off and the 15k resistor is out of cct

the only downside of this configuration is that the small base current
drawn by the transistor causes the neutral light to glow a little
in the dark

a better cct would use a FET instead

hope this helps, even if indirectly


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