EV Diagnostics
Verified EV diagnostic knowledge page

Hyundai C1704

safe relay fault First erase DTC, then check wiring and connector at ECU. C1705 ECU hardware error C1604 ECU over/discharge error C2413 ECU hardware error C2400 Motor signal error

DriveNot yet established by verified evidence. The supplied diagnostic record lists safe-to-drive status as unknown.
ChargeNot yet established by verified evidence. The supplied diagnostic record lists safe-to-charge status as unknown.
ServiceService evaluation is appropriate because Hyundai’s documented diagnostic path requires ECU-area wiring/connector inspection and may lead to MDPS motor or Power Pack assembly replacement if the code returns.
Confidence95%

Quick answer

Hyundai DTC C1704 is identified in the supplied official manufacturer communications as an ECU fail-safe relay fault in the motor-driven power steering (MDPS) diagnostic flow. The documented first steps are to erase the DTC, then check wiring and connectors at the ECU. If the DTC returns, the cited bulletins direct replacement of the MDPS motor or Power Pack assembly, depending on bulletin/version.

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

Video guides

Watch Videos

Relevant videos play here without leaving this diagnostic page.

No sufficiently relevant embeddable video has been accepted for this diagnostic yet.

Videos are supporting material and never override OEM or regulator evidence.

1. What does C1704 mean?

Hyundai DTC C1704 is identified in the supplied official manufacturer communications as an ECU fail-safe relay fault in the motor-driven power steering (MDPS) diagnostic flow. The documented first steps are to erase the DTC, then check wiring and connectors at the ECU. If the DTC returns, the cited bulletins direct replacement of the MDPS motor or Power Pack assembly, depending on bulletin/version.

2. Technical explanation

The verified NHTSA-hosted Hyundai manufacturer communications classify C1704 as an “ECU fail-safe relay fault.” In the cited MDPS repair flow, Hyundai directs technicians to first erase the DTC and inspect wiring and connector condition at the ECU. The cited 2019 bulletin states that if C1704 returns, replace the MDPS motor. The cited 2020 bulletins state that if it returns, replace the MDPS motor or Power Pack assembly. A 2022 MDPS flowchart groups C1704 with power-pack-related DTCs and directs checking R-MDPS connectors and wiring, erasing/rechecking DTCs, and replacing the Power Pack assembly if the DTC remains present.

3. What system is affected?

Motor-Driven Power Steering (MDPS), including the ECU and, depending on the applicable Hyundai bulletin, the MDPS motor or Power Pack assembly.

4. How serious is this code?

Not yet established by verified evidence. The supplied diagnostic record lists severity as unknown.

5. Symptoms you may notice

  • A warning lamp illuminated with DTC(s) present is referenced in the 2022 Hyundai R-MDPS repair-flowchart evidence.
  • No other symptom for C1704 is established by the supplied verified evidence.

6. Possible causes

  • ECU fail-safe relay fault, as identified by the supplied Hyundai manufacturer communications.
  • Wiring or connector condition at the ECU, which Hyundai directs technicians to check.
  • For the 2022 R-MDPS flowchart, C1704 is grouped as power-pack-related; this does not independently establish a failed Power Pack as the cause.

7. Can I still drive the vehicle?

Not yet established by verified evidence. The supplied diagnostic record lists safe-to-drive status as unknown.

8. Can I charge the vehicle?

Not yet established by verified evidence. The supplied diagnostic record lists safe-to-charge status as unknown.

9. What you can safely do

  • Arrange diagnosis by a qualified Hyundai service technician using the applicable MDPS repair procedure.
  • Do not attempt ECU, MDPS motor, or Power Pack replacement based on this code alone.

10. Step-by-step troubleshooting

  1. Erase C1704 and re-check whether it returns, as directed in the cited Hyundai communications.
  2. If it returns, inspect wiring and connectors at the ECU using the applicable Hyundai MDPS procedure.
  3. For the 2022 R-MDPS flowchart, check R-MDPS connectors and wiring, erase/re-check DTCs, and follow the specified repair flow if the code remains present.

11. When to contact service

Service evaluation is appropriate because Hyundai’s documented diagnostic path requires ECU-area wiring/connector inspection and may lead to MDPS motor or Power Pack assembly replacement if the code returns.

12. What the service center may check

  • Confirm C1704 and determine whether it returns after DTC erasure.
  • Check wiring and connector condition at the MDPS ECU.
  • Where the 2022 R-MDPS bulletin applies, check R-MDPS connectors and wiring and follow its power-pack-related DTC flowchart.

13. Possible repair or resolution

  • 2019 Hyundai bulletin evidence: if C1704 returns after the documented steps, replace the MDPS motor.
  • 2020 Hyundai bulletin evidence: if C1704 returns after the documented steps, replace the MDPS motor or Power Pack assembly.
  • 2022 Hyundai R-MDPS flowchart evidence: for persistent C1704 within its power-pack-related DTC group, replace the Power Pack assembly.

14. Affected vehicles

15. Related TSBs / service bulletins

  • Hyundai TSB 19-ST-001H, published April 22, 2019: identifies C1704 as an ECU fail-safe relay fault; erase the DTC and check ECU wiring/connectors; if it returns, replace the MDPS motor. NHTSA document MC-10160106-9999.
  • Hyundai TSB 20-ST-001H, published January 3, 2020: identifies C1704 as an ECU fail-safe relay fault; erase the DTC and check ECU wiring/connectors; if it returns, replace the MDPS motor or Power Pack assembly. NHTSA document MC-10170896-0001.
  • Hyundai TSB 20-ST-001H-1, published August 10, 2020: same cited C1704 diagnostic direction. NHTSA document MC-10179244-0001.
  • Hyundai TSB 20-ST-001H-2, published September 9, 2020: same cited C1704 diagnostic direction. NHTSA document MC-10180981-0001.
  • Hyundai TSB 22-ST-001H, published January 6, 2022: R-MDPS flowchart groups C1704 as power-pack-related and directs wiring/connector checks, DTC erase/recheck, and Power Pack replacement for persistent DTCs. NHTSA document MC-10207815-0001.

16. Recall information

  • Not yet established by verified evidence. The supplied evidence contains manufacturer communications/TSBs, not recall information.

17. Official manufacturer information

Verified sources are NHTSA-hosted Hyundai manufacturer communications: MC-10160106-9999, MC-10170896-0001, MC-10179244-0001, MC-10180981-0001, and MC-10207815-0001.

19. Frequently asked questions

What does Hyundai code C1704 mean?

The supplied Hyundai manufacturer communications identify C1704 as an ECU fail-safe relay fault in the MDPS diagnostic flow.

What is Hyundai’s first documented diagnostic step for C1704?

Erase the DTC, then check wiring and connectors at the ECU.

What if C1704 returns after erasing it?

The cited 2019 bulletin directs MDPS motor replacement. Cited 2020 bulletins direct MDPS motor or Power Pack assembly replacement. The applicable procedure and vehicle configuration determine which bulletin flow applies.

Is C1704 safe to drive with?

Not yet established by verified evidence. The supplied record lists safe-to-drive status as unknown.

Does C1704 affect EV charging?

Not yet established by verified evidence. The supplied record lists safe-to-charge status as unknown.

20. Sources & verification

Verified
Hyundai C1704: safe relay fault First erase DTC, then check wiring and… | EV Diagnostics