EV Diagnostics
Verified EV diagnostic knowledge page

Hyundai P1B77

High Voltage Battery Precharging Fault  DTC P1B25 - Hybrid Battery Safety Plug Or Fuse Circuit NOTE: This bulletin does not apply for just a DTC P1B77 or P1B25, it must also have

DriveNot yet established by verified evidence.
ChargeNot yet established by verified evidence.
ServiceContact a certified IONIQ Hyundai dealer for applicable 2022–2023 US IONIQ 5 or IONIQ 6 campaign work. For a 2016–2017 US Sonata, contact Hyundai service to verify the complete DTC set and bulletin applicability.
Confidence95%

Quick answer

For Hyundai, P1B77 is identified in verified evidence as “High Voltage Battery Precharging Fault.” Its meaning and required repair depend on the vehicle and accompanying DTCs. Do not assume that one bulletin applies from P1B77 alone.

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 P1B77 mean?

For Hyundai, P1B77 is identified in verified evidence as “High Voltage Battery Precharging Fault.” Its meaning and required repair depend on the vehicle and accompanying DTCs. Do not assume that one bulletin applies from P1B77 alone.

2. Technical explanation

Verified Hyundai evidence identifies P1B77 as a high-voltage battery precharging fault. A 2017 Hyundai bulletin for certain Sonata vehicles states that its procedure does not apply for P1B77 or P1B25 by themselves: P1BA7 (Overcharge Detection Active) must also be stored. For applicable vehicles, that bulletin changes the PHEV battery overcharge-detection system from a mechanical Voltage Protection Device switch to an electronic Overvoltage Protection Device within replacement SUB BMS and MAIN BMS units. Separate 2023 Hyundai campaign evidence for certain IONIQ 5 and IONIQ 6 vehicles warns that installing the ICCU fuse before replacing the ICCU can damage the EV battery PRA and cause P1B77. The campaign procedure specifically states to replace the ICCU before installing the fuse, and then inspect the fuse; replace the fuse if it is blown.

3. What system is affected?

High-voltage battery precharging system. The verified 2023 campaign evidence also references the ICCU, ICCU fuse, and EV battery PRA. The verified 2017 Sonata bulletin references the PHEV battery overcharge-detection system, SUB BMS, and MAIN BMS.

4. How serious is this code?

Not yet established by verified evidence.

5. Symptoms you may notice

  • P1B77 may be stored as a diagnostic trouble code.
  • For the 2017 Sonata bulletin, P1B77 may be stored together with P1BA7 and may also be accompanied by P1B25.
  • No driver-visible symptoms are established by the supplied verified evidence.

6. Possible causes

  • For the specified 2023 IONIQ 5 and IONIQ 6 campaign procedure, installing the ICCU fuse before ICCU replacement can damage the EV battery PRA and cause P1B77.
  • Other causes are not yet established by verified evidence.

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

  • Arrange diagnosis by an appropriately qualified Hyundai dealer or service facility.
  • For the 2023 campaign evidence, Hyundai states that the campaign can only be performed at certified IONIQ Hyundai dealers.
  • Do not install or replace the ICCU fuse before the ICCU has been replaced under the applicable campaign procedure.

10. Step-by-step troubleshooting

  1. Confirm the vehicle model year, region, and all stored DTCs before selecting a bulletin or repair path.
  2. For the 2016–2017 US Sonata evidence, confirm whether P1BA7 is stored. The supplied bulletin says its procedure does not apply to P1B77 or P1B25 alone.
  3. For the 2022–2023 US IONIQ 5 and IONIQ 6 evidence, have a certified IONIQ Hyundai dealer determine whether Service Campaign 997 and its ICCU/fuse procedure apply.
  4. No further diagnostic steps are established by the supplied verified evidence.

11. When to contact service

Contact a certified IONIQ Hyundai dealer for applicable 2022–2023 US IONIQ 5 or IONIQ 6 campaign work. For a 2016–2017 US Sonata, contact Hyundai service to verify the complete DTC set and bulletin applicability.

12. What the service center may check

  • Read and record all stored DTCs, including whether P1BA7 and P1B25 are present.
  • For the applicable 2023 campaign procedure, inspect the ICCU fuse only after ICCU replacement; the supplied procedure calls for checking fuse condition with an ohmmeter and replacing the fuse if it is blown.
  • For the applicable 2023 campaign procedure, inspect the fuse after ICCU replacement to determine whether it is blown.
  • No other service checks are established by verified evidence.

13. Possible repair or resolution

  • For the applicable 2023 IONIQ 5/IONIQ 6 campaign procedure: replace the ICCU before installing the fuse; then inspect the fuse and replace it if blown.
  • For the applicable 2016–2017 Sonata bulletin when P1BA7 is also present: the bulletin describes conversion of the PHEV battery overcharge-detection system using new SUB BMS and MAIN BMS units containing electronic OPD functionality.
  • Exact repair eligibility and procedure must be confirmed by the applicable Hyundai bulletin or campaign.

14. Affected vehicles

15. Related TSBs / service bulletins

  • Hyundai Service Campaign 997 / TSB 23-01-060H, published July 17, 2023: ICCU and fuse replacement / ICCU software update procedure. Verified applicability supplied: 2022–2023 US Hyundai IONIQ 5 and IONIQ 6. It warns not to install the fuse before ICCU replacement because EV battery PRA damage and P1B77 can occur.
  • Hyundai bulletin 5NP-X4Q7Y-01, published December 21, 2017. Verified applicability supplied: 2016–2017 US Hyundai Sonata. It applies only when P1BA7 is stored; P1B77 or P1B25 alone do not qualify.

16. Recall information

  • No recall is established by the supplied verified evidence.

17. Official manufacturer information

Official NHTSA-hosted Hyundai manufacturer communications: https://static.nhtsa.gov/odi/tsbs/2023/MC-10240086-0001.pdf ; https://static.nhtsa.gov/odi/tsbs/2023/MC-10240085-0001.pdf ; https://static.nhtsa.gov/odi/tsbs/2017/MC-10127010-9999.pdf

19. Frequently asked questions

What does Hyundai code P1B77 mean?

Verified evidence identifies P1B77 as High Voltage Battery Precharging Fault.

Does the 2017 Sonata bulletin apply if P1B77 is the only code?

No. The supplied Hyundai bulletin states that P1BA7 must also be present; it does not apply for P1B77 or P1B25 alone.

Can replacing the ICCU fuse first cause P1B77?

For the applicable 2023 IONIQ 5 and IONIQ 6 campaign procedure, Hyundai warns that installing the fuse before ICCU replacement can damage the EV battery PRA and cause P1B77.

Can I perform the 2023 campaign at any shop?

The supplied campaign evidence states that it can only be performed at certified IONIQ Hyundai dealers.

20. Sources & verification

Verified
Hyundai P1B77: High Voltage Battery Precharging Fault  DTC P1B25 -… | EV Diagnostics