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How to Troubleshoot the EPS

How to Troubleshoot the EPS 2239

System Indicator
This system has one (without LKAS (Lane Keep Assist System)) or two (with LKAS) indicators on the gauge control module.

EPS Indicator Under
normal conditions, the EPS indicator comes on when turning the vehicle to the ON mode, then turns 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 stores a DTC, and the power assist is turned off or restricted.
  • The EPS indicator will blink when the DTC U3000-55 is detected.

When a problem is detected, the EPS indicator will turn on and remain on until the DTC is erased. There are cases when the indicator remains on until the vehicle is set to the OFF (LOCK) mode as well as other cases where the indicator automatically turns off when the system returns to normal. Under certain conditions, the EPS indicator will turn on even though the system is operating normally; for example when the vehicle is stopped with the engine at high revolutions with constant input from the steering wheel.

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.

LKAS Indicator (amber)
This EPS system works in conjunction with the LKAS. When an LKAS related problem is detected, the LKAS indicator (amber) will come on. However, when the EPS control fails while the LKAS control is activated, the LKAS indicator (amber) will also come on. In this case, the EPS indicator will not come on, but the EPS control unit memorizes the DTC. If the LKAS indicator (amber) comes on, it deactivates the LKAS control. The power assist works as usual after deactivating the LKAS, but it may stop the power assist depending on the detected malfunction.

  • Diagnostic Trouble Code (DTC)
    If the CPU cannot be activated, or if it fails, the EPS indicator comes on, but no EPS DTC is stored.
  • 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 occurrence is stored.
  • The DTCs are stored in the EEPROM (non-volatile memory), therefore the stored DTCs cannot be erased by disconnecting the 12 volt battery. Do the specified procedures to clear the DTCs.

Self-Diagnosis
Self-diagnosis can be classified into three categories:

  • Initial diagnosis: Done right after the engine starts and until the EPS indicator goes off.
  • Regular diagnosis: Done right after the initial diagnosis and continues until turning the vehicle to the OFF (LOCK) mode.
  • Steering diagnosis: Done during regular diagnosis while turning steering wheel.

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 in electrical current draw by the EPS motor. The increase of electric current causes the EPS motor and EPS control unit to heat up. Because this heat adversely affects the system, the control unit monitors the electric current draw of the EPS motor.

When the control unit detects heat build-up in the EPS motor, it reduces the electric current to the EPS 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 turning the vehicle to the OFF (LOCK) mode and the EPS motor cools, the control unit will restore the power assist gradually until it’s fully restored (after about 20 minutes).

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 occurred, and try to reproduce the same conditions for troubleshooting. Find out when the EPS indicator came on, such as while turning, after turning, 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 Use the HDS (Honda Diagnostic System)
NOTE: Make sure the 12 volt battery is in good condition and fully charged

  1. If the system indicator(s) stay on, connect the HDS to the data link connector (DLC).
  2. Turn the vehicle to the ON mode.
  3. Make sure the HDS communicates with the vehicle and the EPS control unit. If it does not, go to the DLC circuit troubleshooting.
  4. Check the diagnostic trouble code (DTC) and the freeze data, for all systems, troubleshoot the power train DTCs first. Then refer to the indicated DTC’s troubleshooting, and do the appropriate troubleshooting procedure..

NOTE:

  • Freeze data indicates the EPS conditions when the first system malfunction that activated the indicator was detected.
  • The HDS can read the DTC, the freeze data, the current data, and other system data.
  • For specific operations, refer to the Help menu that came with the HDS.

How to Retrieve DTCs

  1. 1. With the vehicle in OFF (LOCK) mode, connect the HDS to the data link connector (DLC).
  2. Turn the vehicle to the ON mode.
  3. Make sure the HDS communicates with the vehicle and the EPS control unit. If it does not, go to the DLC circuit troubleshooting.
  4. Follow the prompts on the HDS to display the DTC(s) on the screen. After determining the DTC, refer to the DTC troubleshooting. Do the all systems DTC check, and troubleshoot any power train DTCs first.
  5. Turn the vehicle to the OFF (LOCK) mode.

How to Clear DTCs

  1. With the vehicle in OFF (LOCK) mode, connect the HDS to the data link connector (DLC).
  2. Turn the vehicle to the ON mode.
  3. Make sure the HDS communicates with the vehicle and the EPS control unit. If it does not, go to the DLC circuit troubleshooting.
  4. Clear the DTC(s) by following the screen prompts on the HDS.
  5. Turn the vehicle to the OFF (LOCK) mode.

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