GROUP
CAMPAIGN

Technical Service Bulletin
SUBJECT:

DATE
APRIL 2023

NUMBER
23-01-040H
MODEL(S)
NEXO (FE)

HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT
(SERVICE CAMPAIGN T9A)

This TSB supersedes 22-01-080H to increase Hydrogen fuel sublet from $100 to $150.

 IMPORTANT
*** Dealer Stock and Retail Vehicles ***
Dealers must perform this campaign on all affected vehicles prior to customer retail delivery
and whenever an affected vehicle is in the shop for any maintenance or repair.
Access the Vehicle Information Screen (VIS) via WEBDCS to identify open campaigns.

Description: Some NEXO (FE) vehicles may exhibit charging interruptions during hydrogen charging
due to sensitive leak detection logic diagnostic conditions. This bulletin outlines the procedure to
update the HMU controller software and replace the PRV (Pressure Relief Valve).

STUI
This TSB includes STUI pictures as a requirement. Where indicated, please include a copy
of the RO or last 6 digits of the VIN and date of repair on a piece of paper. Ensure the VIN
and date of repair are clearly visible. Finally, please ensure all captured pictures are
completed according to the steps in this TSB and uploaded to STUI. All claims submitted
that have illegible, incomplete, missing, or incorrect picture(s) are subject to debit.

Applicable Vehicles: Certain 2019MY ~ 2022MY NEXO (FE) vehicles.

NOTICE
•

The TSB repair procedure MUST be performed at an authorized Hyundai NEXO fuel cell
vehicle dealer and by a Hyundai Expert (or above level) technician who has successfully
completed the Fuel Cell Electric Vehicle Training Instructor Led Training course
(SVCHFCEVTRAIN222_1097).

•

Refer to OSHA standard 1910.137 - Electrical Protective Equipment for PPE inspection and
testing requirements and the NEXO shop manual for PPE usage.

Circulate To: General Manager, Service Manager, Parts Manager, Warranty Manager, Service
Advisors, Technicians, Body Shop Manager, Fleet Repair

HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

SUBJECT:

Parts Information:
PART
NUMBER

REMARKS

Pressure Relief Valve (PRV)

35904M5000QQH

1 Each

Sealant Threebond 1211

2145133T02QQH

PART NAME

Hydrogen Leak Detector

IMAGE

No Image

SNOOP RC Leak check fluid

1 tube can be used for about 100
vehicles

None

Part of Dealer Nexo SST Kit

None

Only need if leak detector fails

Warranty Information:
OP CODE

OPERATION & CONDITIONS

20D050R2 If - Hydrogen tank pressure is 1,100 PSI or
less and fuel supply lines are depressurized
(i.e., performed but claimed via separate
repair or campaign TSB).
Then – HMU UPGRADE & PRV
REPLACEMENT

OP
TIME

SUBLET

1.1 M/H

$0.29

20D050R3 If - Hydrogen tank pressure is 1,100 PSI or
less (i.e. customer drove in with low fuel) and
fuel supply lines need depressurization.
Then – DEPRESSURIZE FUEL SUPPLY
LINES AND PERFORM HMU UPGRADE
AND PRV REPLACEMENT

1.5 M/H

$200.29

20D050R4 If - Hydrogen tank pressure is 1,101 PSI or
more
Then – DEFUEL (VENT) TANKS TO 1,100
PSI OR LESS, DEPRESSURIZE FUEL
SUPPLY LINES AND PERFORM HMU
UPGRADE AND PRV REPLACEMENT

2.3 M/H

$200.29

CAUSAL NATURE CAUSE
PART
CODE CODE

35904M5000
QQH

B21

ZZ1

NOTE 1: Submit claim on Campaign Claim Entry Screen
NOTE 2: Op Code 20D050R2 accounts for the related defueling (venting), depressurizing fuel supply
lines, and refueling of vehicle costs being covered via a separate repair claim outside of this TSB.
NOTE 3: Op Codes 20D050R3 and 20D050R4 include $200.00 for transportation of the vehicle to the
fueling station ($50) and fuel to refuel vehicle ($150).
Please DO NOT submit a separate claim with duplicate labor or sublet. If defueling/refueling is
required for overlapping repairs/campaigns, submit the applicable labor operation for
defueling/refueling on ONLY ONE of the claims.
NOTE 4: All Op Codes include $0.29 for Threebond Sealant per vehicle.

TSB #: 23-01-040H

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HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

NOTE 5: If a part that is not covered by this campaign needs replacement while performing this
campaign, and the affected part is still under warranty, submit a separate claim using the same repair
order. If the part is out of warranty, submit a prior approval request for goodwill consideration prior to
the work.
NOTE 6: The incident parts are subject to callback through the normal Warranty Technical Center
(WTC) parts return process. Claim is subject to debit if the part is requested and not returned.
NOTE 7: Claim must include STUI pictures that are clearly visible along with a piece of paper
displaying the last 6 digits of the VIN and date of the procedure. Claims submitted with illegible,
incomplete, missing or incorrect pictures are subject to debit.

TSB #: 23-01-040H

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HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

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HMU Update & Pressure Relief Valve (PRV) Replacement
Perform HMU Update

Defuel tanks to 1,100 PSI (7.58 Mpa)*

Is tank pressure
less than or equal 1,100
PSI (7.58 MPa)

NO

YES

Depressurize fuel supply lines

Depressurize fuel supply lines

Replace Pressure Relief Valve (PRV).

Replace Pressure Relief Valve (PRV)

Repair leak**

NO PASS

Leak check

PASS

Refuel hydrogen tanks

Repair leak**

Depressurize fuel supply lines

Defuel tanks to 1,100 PSI (7.58 Mpa)*

NO PASS

Leak check

PASS
Reinstall
undercovers

STUI photo(s) are required where indicated by STUI camera icon

End of
procedure

*Refer to TSB 22-FL-005H when defueling the hydrogen tanks
**Refer to shop manual to perform leak check and repair leaks
Nexo (FE) > 2019 > 113KW > Hydrogen Storage System > Repair
Procedures> Hydrogen Gas Leak Test > For Hydrogen Storage System
(HSS)

TSB #: 23-01-040H

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HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

NOTICE
•

Check vehicle for outstanding campaigns requiring defueling and perform all repairs

NOTICE

•

•
•
•
•
•
•

•

Verify the vehicle is affected by checking the HMU control unit ROM ID version and
referencing the ROM ID Information Table before updating the control unit software.

!

CAUTION

Run the fuel cell a sufficient amount of time to ensure that the 12-volt auxiliary battery is
sufficiently charged for the update. Turn off the vehicle after 12-volt auxiliary battery is
charged.
Ensure the 12-volt battery will not become discharged during the update by turning off all lights
and accessories, heater/air conditioner, fan, audio, heated seats, rear defroster, etc.
Do not leave the headlight switch in auto mode.
Before performing the update, set the POWER button to the ON position. To set the POWER
button to the ON position, press the button two times without pressing the brake pedal.
Do not start the fuel cell.
Do not turn OFF the POWER button during the update.
Do not disconnect any cables connected to the vehicle or GDS-M during the update

NOTICE
•
•

Confirm your GDS-M has the most recent software version. If not, connect the GDS-M
Mobile to an Internet port, open the GDS-M home page and select “Internet Update.” Refer
to www.hyundaitechinfo.com if necessary.
If you encounter GDS-M related problems, call the GIT Helpline at 888-437-0308.

NOTICE
•

When the vehicle auxiliary 12-volt battery has low voltage, the GDS-M will trigger a Low
Battery Voltage Warning. If this Warning occurs, then perform A or B as follows.
A. Connect the battery to a fully charged battery jump pack or GR8 charger using “Power Supply
Mode” to continue the software update.
B. Select “BACK” to exit the SW update. Then, start the fuel cell and let it run with until the
auxiliary 12-volt battery is sufficiently charged. Return to the software update after charging
the battery to prevent ECM damage.

TSB #: 23-01-040H

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HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

SERVICE PROCEDURE: HMU Update
Connect the VCI-II into the vehicle’s driver side
instrument panel OBD-II port and verify the
device is operational.
Do not set up the trigger module.

NOTICE
•
•

GDS-M control unit upgrading operates with wireless communication ad Wi-Fi direct.
It is possible to perform the update via USB cable between the tablet PC and VCI-II.
Ensure the tablet battery has reasonable charge before starting the update.

NOTICE
•
•

You must initially perform GDS-M HMU Update in Auto Mode.
If the ECM Update starts but then fails in Auto Mode, perform the update in Manual
Mode to recover.

A. Automatic GDS-M Update Procedure
1. Enter the vehicle’s information and on the next screen select ECU Upgrade.
2. Select Auto Mode and then select System, HMU.
3. Read information and select ID check.
4. GDS-M will read the current vehicle ROM ID and check for the newest update event.
5. Select the upgrade event.
"816.FE REGULATOR COMPLEMENTARY LOGIC (HMU SOFTWARE)"
6. If the low battery warning message appears,
then select the BACK arrow
and run the
fuel cell to ensure the battery is adequately
charged for the update.
7. Update (1/2) will begin and progress will be displayed on the bar graph.
8. Update (2/2) will begin and progress will be displayed on the bar graph.
9. After update (2/2) is complete, turn off the ignition for 10 seconds.
10. Turn the ignition to the ON position and press OK to continue according to information displayed
on the screen. Do not start the fuel cell. Do not put into READY mode.
11. Select OK on the final screen and the update is complete.
TSB #: 23-01-040H

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HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

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12. Check for any DTCs created by the update and clear the codes.
13. Start the fuel cell (READY Mode) to confirm if the vehicle is operating properly.

NOTICE
•
•

Only perform the manual update if the automatic update fails.
If automatic update fails, turn the ignition off for about 10 seconds. Place it back into the
ON position to reset the control unit before performing the manual update

B. Manual GDS-M Update Procedure
1. Within the upgrade screen, select Manual Mode, then select upgrade event.
2. Select the control unit part number with reference to the ROM ID Information Table as listed
below in this TSB. Then select Upgrade.
816.FE REGULATOR COMPLEMENTARY LOGIC (HMU SOFTWARE)"
3. Enter the password from the password table located at the below in this TSB and press OK.
4. If the low battery warning message appears,
then select the BACK arrow
and run the
fuel cell to ensure the battery is adequately
charged for the update.
5. Update (1/2) will begin and progress will be displayed on the bar graph.
6. Update (2/2) will begin and progress will be displayed on the bar graph.
7. After update (2/2) is complete, turn off the ignition for 10 seconds.
8. Turn the ignition to the ON position and press OK to continue according to information displayed
on the screen. Do not start the fuel cell. Do not put into READY mode.
9. Select OK on the final screen and the update is complete.
10. Check for any DTCs created by the update and clear the codes.
11. Put the vehicle into READY mode to confirm the vehicle is operating properly.

TSB #: 23-01-040H

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HMU UPDATE & PRESSURE RELIEF VALVE (PRV) REPLACEMENT (SERVICE CAMPAIGN T9A)

SUBJECT:

ROM ID Reference Table
DEL

HMU P/No.

35908-M5000

FE

ROM ID
OLD

NEW

3700R
3500R
3600R
3700R
3910R

4030R

Manual Mode Password Information Tables:
EVENT #

MENU

PASSWORD

816

FE HMU 35908-M5000

0304

TSB #: 23-01-040H

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