How to Troubleshoot the EPS

EPS Indicator

Under normal conditions, the EPS indicator comes on when the ignition switch is turned to the ON (II) position, then goes off after the engine is started. This indicates that the LED and its circuit are operating correctly.
If there is a failure in the system after the engine is started, the EPS indicator will stay on, and the power assist is turned off.

When EPS indicator comes on, the control unit memorizes the DTC. In this case, the control unit will not activate the EPS system after the engine starts again, but it keeps the EPS indicator on.

When DTC 51-01, 51-02 or 51-06 is stored in the control unit, the EPS indicator will stay on until the DTC is erased. When a problem is detected and the EPS indicator comes on, there are cases when the indicator stays on until the ignition switch is turned OFF, and cases when the indicator goes off automatically when the system returns to normal. Even though the system is operating normally, the EPS indicator will come on under the following conditions:

The vehicle speed decreases abruptly from 20 km/h (12 mph) or more (by applying brake), and it is less than 1 km/h (1 mph) and engine speed is 2,000 rpm (min^-1) or above for 5 seconds (continuously) after the abrupt deceleration.
While turning the steering wheel with the vehicle speed of 1 km/h (1 mph) or less for 20 seconds, and the engine speed is 2,000 rpm (min^-1) or above for at least 10 seconds.
When the engine speed is 500 rpm (min^-1) or less, and the vehicle is travelling at a speed of 10 km/h (6 mph) or more for about 3 seconds.

To determine the actual cause of the problem, question the customer about the conditions during which the problem occured, taking the above conditions into consideration.

Diagnostic Trouble Code (DTC)

If the CPU cannot be activated, or it fails, the EPS indicator comes on, but the DTC is not memorized.
The memory can hold any number of DTCs. However, when the same DTC is detected more than once, the most recent DTC is written over the prior DTC, therefore only one occurance is memorized.
The lowest DTC is indicated first. The DTCs are indicated in ascending order, not in the order that they occurred.
The DTCs are memorized in the EEPROM (non-volatile memory) therefore the memorized DTCs cannot be erased by disconnecting the battery. Perform the specified procedures to clear DTCs.

Self-diagnosis

Self-diagnosis can be classified into three categories:

Initial diagnosis: Performed right after the engine starts and until the EPS indicator goes off.
Regular diagnosis: Performed right after the initial diagnosis until the ignition switch is turned OFF.
Steering diagnosis: Performed in case of steering during the regular diagnosis.

The EPS control unit performs the following functions when a problem is detected by self-diagnosis:

1. Turns on the EPS indicator.

2. Memorizes the DTC.

3. Stops power assist and manual steering operation resumes.

NOTE: For DTCs 11-01, 11-02, 12-01, 21-01, 21-02, 22-01 and 35-04 the EPS indicator will go off automatically, and the system returns to normal.

Restriction on Power Assist Operation

Repeated extreme steering force, such as turning the steering wheel continuously back-and-forth with the vehicle stopped, causes an increase of power consumption in the EPS motor. The increase of electric current causes the motor to heat up. Because this heat adversely affects the system, the control unit monitors the electric current of the motor.

When the control unit detects heat build-up in the motor, it reduces the electric current to the motor gradually to protect the system, and it restricts the power assist operation. The EPS indicator does not come on during this function.

When steering torque is not applied to the steering wheel, or when the ignition is turned off and the motor cools, the control unit will restore the power assist gradually until it's fully restored (after about 8 minutes).

Torque Sensor Neutral Position

The EPS control unit stores the torque sensor neutral position in the EEPROM. The torque sensor neutral position must be memorized whenever the gearbox, the motor or EPS control unit is replaced.

NOTE: The torque sensor neutral position is not effected when erasing the DTCs.

How to Troubleshoot DTCs

The troubleshooting procedures assume that the cause of the problem is still present and the EPS indicator is still on. Following the procedure when the EPS indicator does not come on can result in incorrect diagnosis.

1. Question the customer about the conditions when the problem occured, and try to reproduce the same conditions for troubleshooting. Find out when the EPS indicator came on, such as during EPS control, after EPS control, when the vehicle was at a certain speed, etc.

2. When the EPS indicator does not come on during the test-drive, but troubleshooting is done based on the DTC, check for loose connectors, poor terminal contact, etc., in the affected circuit before you start troubleshooting.

3. After troubleshooting, clear the DTC and test-drive the vehicle. Be sure the EPS indicator does not come on.

How to Retrieve DTCs

1. With the ignition switch OFF, connect the HDS (Honda diagnostic system) to the data link connector (DLC) (A) located under the dash on the driver's side of the vehicle.

2. Turn the ignition switch ON (II).

3. Make sure the HDS communicates with the vehicle and the EPS control unit. If it doesn't, troubleshoot the DLC circuit: R18A1 engine model, K20Z2 engine model.

4. Follow the prompts on the HDS to display the DTC(s) on the screen. After determining the DTC, refer to the DTC Troubleshooting.

NOTE: See the HDS Help menu for specific instructions.

How to Clear DTCs

1. With the ignition switch OFF, connect the HDS to the data link connector (DLC) (A) located under the dash on the driver's side of the vehicle.

2. Turn the ignition switch ON (II).

3. Make sure the HDS communicates with the vehicle and the EPS control unit. If it doesn't, troubleshoot the DLC circuit: R18A1 engine model, K20Z2 engine model.

4. Clear the DTC(s) by following the screen prompts on the HDS.

NOTE: See the HDS Help menu for specific instructions.