ENGINE START SYSTEM OPERATION

When the engine switch is pressed with the brake pedal depressed and shift lever in P or N, the main body ECU determines that it is an engine start request.
The certification ECU and other ECUs perform key verification via the LIN communication line. The engine switch indicator light illuminates in green.
The main body ECU activates the D-ACC, D-IG1 and IG2 relays.
The certification ECU outputs a steering UNLOCK signal. The signal is sent to the steering lock ECU via the LIN communication line.
The main body ECU sends an engine start request signal to the ECM.
The ECM sends an ACC cut request signal to the main body ECU.
The ECM and main body ECU activate the ST cut relay.
The main body ECU deactivates the D-ACC relay until the ECU detects an engine start

The ECU reactivates the D-ACC relay and turns off the engine switch indicator light.

SYMBOLS OF MAIN BODY ECU

Symbols of main body ECU	Signals
SSW1/SSW2	Engine switch on (ACC, IG) signal
ACCD	D-ACC relay operation signal
IG2D	IG2 relay operation signal
STR2	ST CUT relay operation signal
STR	Park / neutral position switch signal
STP	Stop light switch signal
TACH	Engine start detection signal
STSW	Starter activation request signal
ACCR	ACC cut request signal

Fig 1: Engine Does Not Start - Wiring Diagram

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Engine does not Start: Description