ERROR_VBAT_NEG_PHASE_RESISTANCE
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Applicable alarms (1)
ERROR_VBAT_NEG_PHASE_RESISTANCE
Likely outcomes — click to expand
Based on 0 missions where this alarm fired in the last 90 days as of 2026-10-13
Aggregated from fleet operations and refreshed daily. Individual outcomes may vary by site and configuration.
Background
Section titled “Background”This alarm occurs when high resistance is detected in the negative battery harness.
Troubleshooting Steps
Section titled “Troubleshooting Steps”graph TD
are-one-or-more-of-the-fasteners-on-the{"<small><b>Step 1</b></small><br/>Question: Are one or more of the fasteners on t..."}
replace-the-power-distribution-board-pd["<small><b>Step 2</b></small><br/>Action: Replace the power distribution board ..."]
replace-the-fasteners-see-the-applicabl["<small><b>Step 3</b></small><br/>Action: Replace the fasteners. See the appl..."]
is-there-any-damage-on-the-battery-harn["<small><b>Step 4</b></small><br/>Action: Is there any damage on the battery ha..."]
replace-the-battery-whether-or-not-dama["<small><b>Step 5</b></small><br/>Action: Replace the battery whether or not d..."]
place-the-aircraft-into-a-dock-and-run{"<small><b>Step 6</b></small><br/>Question: Perform a health check. See UMM: 14...."}
the-aircraft-may-return-to-service("<small><b>Step 7</b></small><br/>Reference: The Aircraft may return to service.")
escalate-to-p2-busbars-on-call{{"<small><b>Step 8</b></small><br/>Escalation: Escalate to P2 Busbars On Call. Updat..."}}
are-one-or-more-of-the-fasteners-on-the -->|Cross-threaded fasteners| replace-the-power-distribution-board-pd
are-one-or-more-of-the-fasteners-on-the -->|Loose fasteners| replace-the-fasteners-see-the-applicabl
replace-the-power-distribution-board-pd --> is-there-any-damage-on-the-battery-harn
replace-the-fasteners-see-the-applicabl --> is-there-any-damage-on-the-battery-harn
is-there-any-damage-on-the-battery-harn --> replace-the-battery-whether-or-not-dama
replace-the-battery-whether-or-not-dama --> place-the-aircraft-into-a-dock-and-run
place-the-aircraft-into-a-dock-and-run -->|Yes| the-aircraft-may-return-to-service
place-the-aircraft-into-a-dock-and-run -->|No| escalate-to-p2-busbars-on-call
style are-one-or-more-of-the-fasteners-on-the fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style replace-the-power-distribution-board-pd fill:#dcfce7,stroke:#22c55e,color:#14532d
style replace-the-fasteners-see-the-applicabl fill:#dcfce7,stroke:#22c55e,color:#14532d
style is-there-any-damage-on-the-battery-harn fill:#dcfce7,stroke:#22c55e,color:#14532d
style replace-the-battery-whether-or-not-dama fill:#dcfce7,stroke:#22c55e,color:#14532d
style place-the-aircraft-into-a-dock-and-run fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style the-aircraft-may-return-to-service fill:#f3e8ff,stroke:#a855f7,color:#581c87
style escalate-to-p2-busbars-on-call fill:#fef3c7,stroke:#f59e0b,color:#78350f Hover or focus a block to preview it. Select the block to keep the preview open.
1 question
Are one or more of the fasteners on the negative battery harness to power distribution board (PDB) bolted joints cross-threaded or loose? For bolted joint locations, see High Resistance Inspection Locations.
2 action
Replace the power distribution board (PDB). The busbar terminal threads may be damaged and the fastener may not seat even when it is installed correctly. For steps, see:
- UMM: Remove Power Distribution Board (PDB)
- UMM: Install Power Distribution Board (PDB)
- UMM: Remove Power Distribution Board (PDB)
- UMM: Install Power Distribution Board (PDB)
3 action
Replace the fastener(s). See the applicable steps in:
- UMM: Remove Busbar to Power Distribution Board (PDB) Connectors
- UMM: Install Busbar to Power Distribution Board (PDB) Connectors
NOTE: Even when a torque driver clicks without turning the fastener, it does not necessarily indicate that the joint is good
- UMM: Remove Busbar to Power Distribution Board (PDB) Connectors
- UMM: Install Busbar to Power Distribution Board (PDB) Connectors
NOTE: Even when a torque driver clicks without turning the fastener, it does not necessarily indicate that the joint is good
4 action
Is there any damage on the battery harness wires and crimps? Note any visible issues in the Discrepancy.
5 action
Replace the battery (whether or not damage is visible). For steps, see:
- UMM: Remove Battery
- UMM: Install Battery
- UMM: Remove Battery
- UMM: Install Battery
6 question
Perform a health check. See UMM: 14.4.1.h Perform a Zip Maintenance Health Check. Does the issue return?
7 reference
The Aircraft may return to service.
8 escalation
Escalate to P2 Busbars On Call.
Update the ticket with details of the inspections conducted and any maintenance procedures and wait for an engineering response.
Update the ticket with details of the inspections conducted and any maintenance procedures and wait for an engineering response.
Resolution note
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