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Kia C1704

Safe Relay Fault First, erase DTC. Then check the wiring and connector at the ECU. C1705 ECU Hardware Error C1604 ECU Over/Discharge Error C2413 ECU Hardware Error C2400 Motor Sign

DriveNot yet established by verified evidence.
ChargeNot yet established by verified evidence.
ServiceService is appropriate because the verified Kia TSB provides a specific MDPS diagnostic and replacement path. Driveability and urgency are not established by the supplied evidence.
Confidence95%

Quick answer

Kia DTC C1704 is identified in verified Kia TSB evidence as an MDPS ECU fail-safe relay fault. The documented procedure is to erase the DTC, then check the wiring and connector at the ECU. If the DTC returns, the TSB directs replacement of the MDPS motor.

This page separates verified manufacturer/regulator evidence from supporting material. Unsupported causes, repairs or safety conclusions are not guessed.

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1. What does C1704 mean?

Kia DTC C1704 is identified in verified Kia TSB evidence as an MDPS ECU fail-safe relay fault. The documented procedure is to erase the DTC, then check the wiring and connector at the ECU. If the DTC returns, the TSB directs replacement of the MDPS motor.

2. Technical explanation

Verified Kia TSB CHA084 revisions list C1704 as “ECU Fail-Safe Relay Fault.” In the same repair guidance, Kia specifies: first erase the DTC, then check the wiring and connector at the ECU. If C1704 returns, replace the MDPS motor. The supplied evidence does not establish the underlying electrical failure mechanism beyond this fault description and diagnostic path.

3. What system is affected?

MDPS (motor-driven power steering) system; ECU wiring/connector and MDPS motor are referenced by the verified TSB evidence.

4. How serious is this code?

Not yet established by verified evidence.

5. Symptoms you may notice

Not yet established by verified evidence.

6. Possible causes

  • MDPS ECU fail-safe relay fault, as named by the verified Kia TSB evidence.
  • Wiring or connector condition at the ECU is a documented inspection item. A specific wiring or connector defect is not established by the supplied evidence.
  • If the DTC returns after erasure and the documented check, the TSB directs MDPS motor replacement; the evidence does not establish a more specific component-level root cause.

7. Can I still drive the vehicle?

Not yet established by verified evidence.

8. Can I charge the vehicle?

Not yet established by verified evidence.

9. What you can safely do

  • Have the code evaluated using the documented Kia procedure.
  • Use a qualified service provider for MDPS diagnosis and any component replacement.
  • Do not perform high-voltage repair work; no high-voltage repair procedure is provided or supported by the supplied evidence.

10. Step-by-step troubleshooting

  1. Erase DTC C1704.
  2. Check the wiring and connector at the ECU.
  3. If C1704 returns, replace the MDPS motor.

11. When to contact service

Service is appropriate because the verified Kia TSB provides a specific MDPS diagnostic and replacement path. Driveability and urgency are not established by the supplied evidence.

12. What the service center may check

  • Confirm DTC C1704.
  • Erase the DTC as directed in Kia TSB CHA084.
  • Check wiring and connector condition at the ECU.
  • Determine whether C1704 returns after the documented steps.

13. Possible repair or resolution

  • If C1704 returns, the verified Kia TSB directs replacement of the MDPS motor.

14. Affected vehicles

15. Related TSBs / service bulletins

  • Kia TSB CHA084, revisions R3 through R8, is supported by the supplied NHTSA manufacturer-communication records. These revisions identify C1704 as an ECU Fail-Safe Relay Fault and specify: erase the DTC, check ECU wiring and connector condition, and replace the MDPS motor if the code returns.
  • NHTSA record MC-10202226-0001, published 2021-10-05: https://static.nhtsa.gov/odi/tsbs/2021/MC-10202226-0001.pdf
  • NHTSA record MC-10189545-0001, published 2021-03-25: https://static.nhtsa.gov/odi/tsbs/2021/MC-10189545-0001.pdf
  • NHTSA record MC-10183333-0001, published 2020-11-25: https://static.nhtsa.gov/odi/tsbs/2020/MC-10183333-0001.pdf
  • NHTSA record MC-10183332-0001, published 2020-11-04: https://static.nhtsa.gov/odi/tsbs/2020/MC-10183332-0001.pdf
  • NHTSA record MC-10168850-0001, published 2019-11-26: https://static.nhtsa.gov/odi/tsbs/2019/MC-10168850-0001.pdf
  • NHTSA record MC-10167301-0001, published 2019-10-15: https://static.nhtsa.gov/odi/tsbs/2019/MC-10167301-0001.pdf

16. Recall information

  • Not yet established by verified evidence.

17. Official manufacturer information

Verified official evidence consists of Kia TSB CHA084 revisions R3–R8 published through NHTSA manufacturer communications. The supplied applicability data lists U.S.-market Kia Niro (2015–2022), Optima (2015–2022), Sorento (2015–2022), and Soul (2015–2022), with overlapping year ranges in the source data. Exact applicability should be confirmed against the vehicle and current Kia service information.

19. Frequently asked questions

What does Kia C1704 mean?

Verified Kia TSB evidence identifies C1704 as an “ECU Fail-Safe Relay Fault” in the MDPS system.

What does Kia direct technicians to do for C1704?

The documented sequence is to erase the DTC, then check the wiring and connector at the ECU. If the code returns, replace the MDPS motor.

Is C1704 safe to drive with?

Not yet established by verified evidence.

Does C1704 affect EV charging?

Not yet established by verified evidence.

Which vehicles may be covered by the supplied applicability data?

The supplied data lists U.S.-market Kia Niro, Optima, Sorento, and Soul model years spanning 2015–2022, with overlapping ranges. Exact vehicle applicability is not established without confirming the specific vehicle and current Kia information.

20. Sources & verification

Verified
Kia C1704: Safe Relay Fault First, erase DTC. Then check the wiring… | EV Diagnostics