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Drive BY wire Throttle body TPS Main and Sub

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi chaps,

Can someone please send me a link with what is main and sub on Drive by wire throttle body.

On typical drive by wire, I understand we have

+ and - for motor

ground - is it chassis or ecu?

signal - is this using voltage from APP to open motor?

TPS Main - by crank?

TPS Sub - for traction?

What I want to understand is when you open throttle on APPs, is signal sent to ECU which is then transmitted to the throttle body so it opens the plate by certain amount?

what is typical voltage seen on Motor when throttle is closed and when wot. I assume it can't be constant 12v as motor will then fully open the flap.

many thanks

Both the Accelerator Pedal Position (APP) and Throttle Body Position (TPS) have redundant sensors (Main and Tracking, Main / Sub, Sig1 / Sig2, or other names). The idea is the ECU can compare the signals and if they don't agree then generate a fault instead of believing the one that says "use 100% throttle".

The ECU Drive by Wire Strategy determines how to map the pedal position into a target throttle position, then activate the Motor +/- to achieve that target position based one the TPS feedback. The Servo Motor will usually vary between 12V on the Motor+ and 0V on the Motor- to open the throttle, and 0V on the Motor+ and 12V on the Motor- to close the throttle. The ECU will use Pulse Width Modulation to switch between these two states at a fairly high frequency often 5000 - 10000 cycles per second (hz). The motors can draw several amps and generally the Motor+/- need to use 18ga or thicker wire.

So you need to provide the proper 4 signals to the ECU, then configure/calibrate the ECU to understand the relationship between the two pairs of sensors (sometimes Main is 0-5V, Sub is 5-0V, or Sub is 0-2.5V). Calibration will figure that out. If using an OEM ECU, you often don't have access to the necessary calibration, and have to use Pedals and Throttle Bodies that are compatible with the OEM signaling. Standalone ECUs are a bit more flexible here.

Hope that helps you understand how drive-by-wire works.


on my apps, one volt ref is 5v and other is 2.5

signal on one goes from 0.5 to 1.5v for 2.5v

signal on one goes from 1 to 3 volt for 5v ref

So on one range is 1v and other is 2v.

would it be ecu consider one source to be half of other so .1 needs to match 0.05 of sub signal?

I don't think you have the pinout correct. Normally I would expect the VRef to be the same for both sensors (ie. 5V +/- from your ECU). I would expect the signal output to vary between 0V and VRef, or one signal it may only go VRef/2 (so your 2.5V).

sure vref meaning voltage reference or ecu reference?

I am trying to diagnose a car issue where it is coming u with high throttle position voltage and as part of it, I have checked over 6 times but one ref is 5 and other is 2.5

"I would expect the signal output to vary between 0V and VRef, on one signal it may only go VRef/2 (so your 2.5V)."

I don't understand the second part of the answer. I believe you are stating both should have 5v ref voltage thus both signal should be the same?

What is the brand and part number of the DBW Throttle? Some older style throttles used to use a Tracking signal that wasn't full scale and that would top out around the 2.5V~3V region.

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