DIY - Bypassing Tire Pressure Warning System (TPWS / TPMS)

[Tamago]

Originally Posted by CTScott

No shunting is required. The two wires we are disconnecting are both 12 V analog signals which the ECU is pulling through A to D converters. We shouldn't be able to pick up enough noise to cause a false signal detection.

i thought speed and tach signals were both pulse signals.... ?

[CTScott]

Originally Posted by Tamago

i thought speed and tach signals were both pulse signals.... ?

They are frequency modulated pulses. The TPMS microcontroller pulls them in through an analog input.

[Tamago]

Originally Posted by CTScott

They are frequency modulated pulses. The TPMS microcontroller pulls them in through an analog input.

ah cool so where they enter the ENGINE ecu they're pulse signals, then they go out to the cluster as pulses (correct me if i'm wrong, i recollect setting up a Defi VSD heads up display, and grabbed pulse signals for tach/speed) and the ECU also sends analog outputs to the TPMS?

do you have a wiring diagram of the ECU?

[CTScott]

Originally Posted by Tamago

ah cool so where they enter the ENGINE ecu they're pulse signals, then they go out to the cluster as pulses (correct me if i'm wrong, i recollect setting up a Defi VSD heads up display, and grabbed pulse signals for tach/speed) and the ECU also sends analog outputs to the TPMS?

do you have a wiring diagram of the ECU?

The ECU sends the same pulsed signal to the cluster and the TPWS. The Combo Meter has a microcontroller, which reads the tach and VSS inputs directly, as well as a CAN bus interface to get the odo data and MIL input from the ECU. All of the "data" signals are 12 V, so the microcontrollers have to level shift them to use them (via optoisolator, A-D, etc.).

The Defi's micro would have to do the same thing. By the way, was the Defi VSD worth the money?

For the wiring diagrams, I just have the 09 service manual.

[Tamago]

Originally Posted by CTScott

The ECU sends the same pulsed signal to the cluster and the TPWS. The Combo Meter has a microcontroller, which reads the tach and VSS inputs directly, as well as a CAN bus interface to get the odo data and MIL input from the ECU. All of the "data" signals are 12 V, so the microcontrollers have to level shift them to use them (via optoisolator, A-D, etc.).

The Defi's micro would have to do the same thing. By the way, was the Defi VSD worth the money?

For the wiring diagrams, I just have the 09 service manual.

i've installed 3 sets.. one on my xA the base VSD.. it was essential to life for me until it was vandalized :( it would record max speed/RPM which worked well for primitive datalogging at autocross..

the second one was the VSD that would hook up to the LINK system.. this one went in the yaris. speed/tach on the windshield is awesome..

i now have a VSD-X for my xA.. it has its own screen. i had it installed for a bit then removed it. it's a nice piece but a little OTT for this build. i believe DEFI has discontinued all their HUD's..