NOTE
Be sure the battery is fully charged.
Main Harness [B] Vehicle-down Sensor [C]
Special Tool - Measuring Adapter: 57001-1700

Vehicle-down Sensor Input Voltage Connections to Adapter: Digital Meter (+) → R (sensor BL) lead Digital Meter (–) → BK (sensor BR/BK) lead

Input Voltage
Standard: DC 4.75
5.25 V
If the reading is within the standard, check the output voltage (see Vehicle-down Sensor Output Voltage Inspection).
If the reading is out of the standard, remove the ECU and check the wiring for continuity between main harness connectors.
Special Tool - Hand Tester: 57001-1394
Disconnect the ECU and sensor connectors.
Wiring Continuity Inspection ECU Connector [A] ←→ Vehicle-down Sensor Connector [B] BL lead (ECU terminal 9) [C] BR/BK lead (ECU terminal 13) [D]

If the wiring is good, check the ECU for its ground and power supply (see ECU Power Supply Inspection in the Fuel System (DFI) chapter).
If the ground and power supply are good, replace the ECU (see ECU Removal/Installation in the Fuel System (DFI) chapter).
Vehicle-down Sensor Installation
Vehicle-down Sensor Output Voltage InspectionLights and Switches Operation Inspection
First Step
Set the gear position in the neutral position.
Turn the ignition switch to ON.
The following lights should go on according to below table.
If the following light does not go on, inspect the meter
unit (see Meter Unit Inspection in the Electrical System
chapter).
...
Thermostat Removal
Remove:
Fuel Tank (see Fuel Tank Removal in the Fuel System
(DFI) chapter)
Air Cleaner Housing (see Air Cleaner Housing Removal
in the Fuel System (DFI) chapter)
Throttle Body Assy (see Throttle Body Assy Removal in
the Fuel System (DFI) chapter)
Throttle Body Assy Holder Clamp [A]
...
Stick Coil Removal
Remove the air cleaner housing (see Air Cleaner Housing
Removal in the Fuel System (DFI) chapter).
Disconnect the stick coil connectors [A].
Pull out the stick coils [B] upward.
First, turn the stick coil by 90 degrees, and then pull it out
by twisting the coil head to the left and righ ...