SUBJECT:

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

SERVICE PROCEDURE: Depleting Residual Fuel Supply Pressure & Defueling
1.

Place the vehicle in READY mode using the
START / STOP push button. Photograph the fuel
gauge level and a paper showing the last 6 digits
of the VIN or RO #, and the date of defueling.
Similar to the photo to the right.

STUI
Using STUI, photograph the fuel gauge.
Include in the photos a piece of paper
containing the last 6 digits of the VIN or
the RO #, and the date of the defueling.
Ensure the photo is in focus and captures
the fuel gauge display, odometer, and
note. Upload the photo to STUI.

2.

Connect the GDS-M, select the HMU, and then
confirm the storage tank pressure.

3.

If storage tank pressure is less than or equal to
1,100 PSI, then deplete residual fuel supply
pressure by referring to TSB 22-FL-005H—
VENTING NEXO FUEL CELL ELECTRIC
VEHICLES or the latest version.

4.

If storage tank pressure is greater than 1,100
PSI, then defuel storage tanks to less than 1,100
PSI and deplete residual fuel supply pressure by
referring to TSB 22-FL-005H—VENTING NEXO
FUEL CELL ELECTRIC VEHICLES or the latest
version.

TSB #: 23-01-040H

Icon illuminates when the
vehicle is in READY mode.

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

12 volt and High Voltage Circuit Disconnection
1.

In the rear cargo area, remove the floorboard and
cargo tray to access the 12 volt battery connector
and high voltage battery Safety Plug.

TSB #: 23-01-040H

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

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2.

3.

Disconnect the 12 volt battery negative (-)
connector.

!

WARNING

•

Electrocution hazard - Refer to the shop manual - Battery Control System
> High Voltage Battery Handling Guide and follow the High Voltage Shutoff Procedure.

•

Before performing the service procedure, ensure proper Personal
Protection Equipment (PPE) is worn to prevent injury. Verify PPE is not
expired and in proper working condition.

Remove the metal shield to access the High
Voltage Safety Plug.

TSB #: 23-01-040H

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

4.

Follow A-D below to remove the orange high
voltage safety plug.
Store the removed safety plug in a secure location
outside and away from the vehicle.

5.

Wait 5+ minutes to allow the high voltage system
capacitor to discharge.

TSB #: 23-01-040H

Safety Plug Removal

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

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6.

Open the hood. Remove the junction box trim and
cover.
High voltage junction box cover: Assembly bolt
torque 7.2~8.7lb-ft
(1.0 ~ 1.2 kgf.m, 9.8 ~ 11.8 N.m)

Junction Box Trim

HVJB Cover

7.

Using a Digital Volt Ohm Meter (DVOM), measure
the voltage across the inverter positive and
negative bus bar terminals to inspect for capacitor
discharge. If the measured voltage is below 30
volts, the High Voltage Circuit is properly shut
down.

!
•

DANGER
Electrocution hazard - The High
Voltage Junction Box (HVJB) may be
electrically energized up to 450 volts.

TSB #: 23-01-040H

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

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8.

Close the manual valves on all 3 hydrogen tanks.
Using a 6mm Allen wrench turn the manual valve
clockwise until it stops.
Exceeding closing torque specification, may
damage the manual valve.
Closing Torque:
3.6 ~ 7.2 lb-ft (4.9 ~ 9.8 Nm)

NOTICE
•

9.

Some components of the manual valve
may be damaged if over-torqued.

Remove the pressure relief valve (PRV) (A) using
a 24mm socket & ratchet. Turn the PRV
counterclockwise to remove. Use a 32mm wrench
to hold the Regulator while removing the PRV.

A

NOTICE
•

Be careful not to damage the fuel
supply tube and regulator mounting
bracket.

TSB #: 23-01-040H

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

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10.

Remove the PRV sealant using a razor blade.

NOTICE
•

•

Ensure work area cleanliness to prevent
foreign substances from entering the
PRV openings to prevent clogging the
PRV.
Do not use an air gun to remove foreign
substances.

AFTER
CLEANING

BEFORE
CLEANING

11.

Install the new PRV (B) turning it clockwise.
Tightening Torque:
54.2 ~65.8 lb-ft (73.5~89.2 Nm)

B

i Information
•

Keep the PRV vertical during
installation so that internal components
will not fall out of the PRV.

TSB #: 23-01-040H

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12.

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

Before applying sealant in the next step, take a
photograph of the newly installed PRV and a paper
showing the last six digits of the VIN or RO #, and
the date of installation. Similar to the photo to the
right.

STUI
Using STUI, photograph the newly
installed PRV. Include in the photo a
piece of paper containing the last 6
digits of the VIN or the RO #, the date of
the installation. Ensure the PRV, and
note are captured and in focus. Upload
the photo to STUI.

13.

Apply the sealant (C) between the PRV and the
body of the high-pressure regulator.

NOTICE
•

Use gas detector or Snoop liquid leak
detector to test if there is any gas
leakage.

•

Do not apply Snoop liquid on the part
where the sealant is applied.

•

If there is any leakage on the part where
the sealant is applied, the sealant may
inflate.

•

Apply the sealant by using the nozzle
included in the box.

•

TSB #: 23-01-040H

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

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14.

Open the manual valves on all 3 hydrogen tanks.
Using a 6mm Allen wrench turn the manual valve
counter-clockwise until it stops then rotate manual
valve one half turn clockwise.
Exceeding opening torque specification, may
damage the manual valve.
Opening Torque:
3.6 ~ 7.2 lb-ft (4.9 ~ 9.8 Nm)

NOTICE
•

Some components of the manual valve
may be damaged if over-torqued.

15.

Reconnect 12-volt and high-voltage batteries. Refer to page 10.

16.

With the vehicle in ready mode, perform a leak check of lines, fittings and components removed
and/or replaced, using a Hydrogen leak detector.
Refer to the shop manual:
Nexo (FE) > 2019-2022 > 113KW > Hydrogen Storage System > Repair Procedures>
Hydrogen Gas Leak Test > For Hydrogen Storage System (HSS)
If no leak is found, then proceed to the next step. Do not reinstall the under covers until final leak
check is performed.
If a leak is found. Refer to TSB 22-FL-005H—VENTING NEXO FUEL CELL ELECTRIC VEHICLES
to perfom “Preparation for Replacement of Hydrogen Components” and “Depleting Residual Fuel
Supply Pressure”. Repair the leak(s), then perform this step again until no leak is found.

17.

Refuel hydrogen storage tanks to full at a local hydrogen station.
Refer to the station websites below to confirm station availability before driving or towing vehicle to
the station:
• https://cafcp.org/stationmap
• https://h2-ca.com/

TSB #: 23-01-040H

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18.

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

After refueling the vehicle, use the Push Button
Start Stop (PBSS) switch and place the vehicle
systems into the READY mode. Photograph the
fuel level gauge and a paper showing the last six
digits of the VIN or RO #, and the date of refueling.
Similar to the photo to the right.

STUI
Using STUI, photograph the fuel gauge.
Include in the photo a piece of paper
containing the last 6 digits of the VIN or
the RO #, the date of the refueling.
Ensure the fuel gauge display,
odometer, and note are captured and in
focus. Upload the photo to STUI.
19.

After the Hydrogen tanks have been refueled. Put the vehicle on a lift and place the vehicle into
READY mode using the PBSS. Perform a leak check of hydrogen fuel components that were
replaced, using a Hydrogen leak detector.
Refer to the shop manual:
Nexo (FE) > 2019-2022 > 113KW > Hydrogen Storage System > Repair Procedures>
Hydrogen Gas Leak Test > For Hydrogen Storage System (HSS)

20.

If a leak is found. defuel tanks to 1,100 PSI or less and Refer to TSB 22-FL-005H—VENTING
NEXO FUEL CELL ELECTRIC VEHICLES “Preparation for Replacement of Hydrogen
Components” and “Depleting Residual Fuel Supply Pressure”. Repair the leak(s), then perform
steps 15 - 19 on pages 17 and 18 again until no leak is found.

21.

If no leak is found, then replace the undercovers.

22.

The procedure is complete.

TSB #: 23-01-040H

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