Description of On-Board Diagnostics

General Troubleshooting Information
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 any trouble in the system after the engine is started, the EPS indicator will stay on, and the power assist is turned off. When EPS indicator light 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 12, 16, 17, 18 or 67 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:

Condition 1:
^ The vehicle was traveling at least 12.4 mph (20 km/h), then
^ A rapid change in vehicle speed was detected, then
^ The vehicle (or the vehicle speed sensor signal) stopped for at least 5 seconds
^ The engine speed was still 1,640 rpm or higher for at least 5 seconds

Condition 2:
After the vehicle (or the vehicle speed sensor signal) has stopped for at least 10 seconds, yet the engine speed is 1,640 rpm or higher for at least 20 seconds.

Condition 3:
When the engine speed is 280 rpm or less, and the vehicle is traveling at a speed of 6.2 mph (10 km/h) or more for 3 seconds.

To determine the actual cause of the problem, question the customer about the conditions during which the problem occurred, 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 a large 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 occurrence is memorized.
^ The DTCs are indicated repeatedly until the ignition switch is turned OFF.
^ If the DTC is not memorized, the EPS indicator blinks.
^ The DTCs are memorized in the EEPROM (nonvolatile 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 two 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.

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 begins.

NOTE:
^ When DTC 23 (a problem with the circuit for engine speed signal) is detected, the power assist will return to normal when the vehicle speed is 1 mph (1 km/h) or above.
^ For DTCs 22, 23, 64, or 66 the EPS indicator goes off automatically when the system returns to normal. For all other codes, the EPS indicator goes off when the system is OK after the ignition switch is turned from OFF to ON (II).

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 approximately 15 minutes maximum).