Honda Fit: EPS System Description

Second generation (2007-2024) / Honda Fit 2007-2024 Repair Manual / Chassis / Steering / Electric Steering / EPS System Description

EPS Control Unit Inputs and Outputs for Connector A (11P)

Terminal Number	Wire color	Terminal sign (Terminal name)	Description	Signal
1	PUR	IG-1 (Ignition 1)	Power source for Activating the system	With ignition switch ON (II): battery voltage
3	RED	F-CAN L (F-CAN LO)	F-CAN communication Circuit	With ignition switch ON(ll): Pulses (1.5-2.5 V)
5	WHT	F-CAN H (F-CAN HI)	F-CAN communication Circuit	With ignition switch ON (ll): Pulses (2.5-3.5 V)
6	PUR	MG2 (Motor ground)	Ground for the EPS Motor	???
7	BLU	K-LINE (Data link connector)	Communicates with HDS	With service check signal opened: about 9-11 V
8	ORN	MG1 (Motor ground)	Ground for the EPS Motor	???
9	LT BLU	NEP (Engine speed pulse)	Detects engine Speed signal	With engine running: pulses
10	BLK	PG (Power ground)	Ground for the EPS control unit	Continuity to ground
11	WHT	+B (Plus battery)	Power source for the Actuator EPS motor	Battery voltage at all times

EPS Control Unit Inputs and Outputs for Connector B (16P)

Terminal Number	Wire color	Terminal sign (Terminal name)	Description	Signal
1	YEL	Vcc (Voltage common)	Power source for torque sensor	With engine running: about 10 V
2	BLU	Main (main voltage)	Detects torque sensor signal	Turn to the right: about 2.5-3.3 V (increase) Turn to the left: about 2.5-1.7 V (decrease)
3	WHT	SE (Sensor earth)	Ground for the torque sensor	Continuity to ground
4	RED	Sub (Sub voltage)	Detects torque sensor signal	Turn to the right: about 2.5-1.7 V (decrease) Turn to the left: about 2.5-3.3 V (increase)
5	GRN	Vref (Reference voltage)	Reference voltage for torque sensor	With engine running: about 3.3 V
7	GRN	R1 (Motor angle sensor 1)	Detects EPS motor angle sensor signal	With engine running: pulses (0-5 V)
8	GRY	SG (Sealed ground)	Ground for the sealed line	???
9	PNK	R2 (Motor angle sensor 2)	Detects EPS motor angle sensor signal	With engine running: pulses (0-5 V)
10	LT BLU	S2 (Signal 2)	Detects EPS motor angle sensor signal	With engine running: pulses (0-5 V)
11	GRY	S4 (Signal 4)	Detects EPS motor angle sensor signal	With engine running: pulses (0-5 V)
12	YEL	S1 (Signal 1)	Detects EPS motor angle sensor signal	With engine running: pulses (0-5 V)
13	RED	S3 (Signal 3)	Detects EPS motor angle sensor signal	With engine running: pulses (0-5 V)
14	BLU	MV	Drive the EPS motor	???
15	RED	MU	Drive the EPS motor	???
16	GRN	MW	Drive the EPS motor	???

System Outline

This vehicle is equipped with electrical power steering (EPS). The driver's steering force is assisted by an electric motor at the steering gearbox. Compared to a hydraulic assist power steering system, EPS is more efficient because it does not need an engine driven oil pump to generate hydraulic pressure.

The EPS control unit monitors and controls the EPS motor's assisting force to match driving conditions.

Low vehicle speeds: High power assist (for easy handling)
High speed driving: Low power assist (for stable driving)
Low speed to high speed driving: Change smoothly from high assist to low assist

Steering Gearbox

The steering force from the steering wheel is sent to the pinion shaft. The torque sensor measures the difference between the force applied to the pinion shaft and the resistance to turning the wheels due to road friction, and converts it to a voltage signal which is sent to the EPS control unit. Based on this signal, the EPS control unit controls the current to the EPS motor. The EPS motor shaft gear rotates the worm wheel gear which is part of the pinion shaft. This becomes the assist force in the steering system.

System Operation

The EPS control unit controls the EPS motor by these signals:

Vehicle speed signal (from ECM/PCM)
Engine speed signal (from ECM/PCM)
EPS motor angle sensor signal
Torque sensor signal

At idle or low vehicle speeds, the EPS control unit sends a signal to the ECM/PCM to increase the engine idle speed to prevent the engine from stalling.

When the EPS control unit detects a failure in the system, it stores a DTC and sends a signal to the gauge control module to turn the EPS indicator on.

EPS motor operation

The EPS uses an efficient brushless DC type motor. The EPS motor control circuit is composed of a system control CPU, the field-effect transistor (FET) drive circuit, the H type FET bridge, the power relay, the fail-safe relay, the electric current sensor, and the EPS motor. From the input sensor signals, the CPU calculates and duty cycles outputs the appropriate three-phase current for the FET drive circuit. This operation is duty controlled.

Power relay (built into the EPS control unit)

When the system is operating normally, the CPU turns the power relay on, and the power is provided to the FET bridge. When the CPU detects a failure in the system which has the demand to shut down the system, the CPU turns the power relay off.

Fail-safe relay (built into the EPS control unit)

When the system is operating normally, the CPU turns the fail-safe relay to on, and the power is provided to the EPS motor. When the CPU detects a failure in the system which has the demand to shut down the system, the CPU turns the fail-safe relay off at the same time it turns the power relay off. This relay is a fail-safe in the event the power relay is faulty and does not turn off.

Electric current detection circuit

An electric current detection circuit monitors the current of each phase circuit to the motor, and sends a signal to the CPU.

Honda Fit: EPS System Description

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