P0B35

Code

Generic P — Powertrain

High Voltage Service Disconnect Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 38 RU: 26

AI status

Completed

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Page language: EN

Causes

Open or high-resistance wiring in the HV service disconnect circuit
Connector corrosion, bent pins, or poor mating at the service disconnect or control module
Service disconnect switch physically open (removed for service)
Short to ground in the wiring or damaged insulation contacting chassis
Failed/disconnected service-disconnect sensor or interlock switch
Blown fuse, faulty relay, or intermediate harness connector

Symptoms

Malfunction Indicator Lamp (MIL) or HV-system warning lamp illuminated
HV system disabled or vehicle enters limp mode (reduced power)
No hybrid/EV drive or combustion engine may refuse to start in some hybrids
Inability to charge or enable the high-voltage system
Stored P0B35 and possibly related HV interlock codes in memory

What to check

Read freeze-frame and all pending/related DTCs with a compatible scan tool
Visually inspect the service disconnect plug, interlock switch, and surrounding wiring for damage, corrosion, contamination, or missing parts
Verify connectors are fully seated and locking tabs engaged at the service disconnect and HV junctions
Check fuses and relays related to the HV interlock/service disconnect circuit
Perform continuity and resistance checks between the service disconnect switch and control module (with HV system de-energized and following manufacturer safety procedures)
Measure circuit voltage at the control module pin while operating the service disconnect (observe safety protocols)

Signal parameters

Normal/Connected: control input typically reads logic HIGH or expected reference voltage when service disconnect is closed (varies by manufacturer; often near 5V or pack-monitor logic level)
Fault/Disconnected: voltage low or near 0V (logic LOW) when service disconnect is open or circuit shorted to ground
Continuity: near 0–1 ohm across closed interlock contacts; open/infinite when disconnected (measure with system de-energized)
Diagnostic tool: scan-tool status should show 'service disconnect = connected' when closed and 'disconnected' when open (if supported)

Diagnostic algorithm

Safety first — follow manufacturer high-voltage safety procedures. Disable HV system and isolate the battery before touching HV wiring.
Retrieve freeze-frame data and note conditions (ignition state, pack voltage, ambient temp). Scan and record all related codes.
Visually inspect the service disconnect assembly, connectors, harness routing, and mounting for obvious damage, corrosion, or signs of melting/water intrusion.
Verify the service disconnect is fully installed and mechanical interlocks/locking tabs engaged. Reinstall if loose; clear codes and re-test.
With the vehicle powered down and HV system isolated, check continuity across the service-disconnect interlock contacts. Expected: low ohms when installed/closed, open when removed.
With a qualified procedure and low-voltage references or as directed by OEM, measure the signal voltage at the control module pin while operating the interlock (or with harness harness back-probed). Confirm it changes between expected high and low states.
If the signal is low when the switch should be closed, inspect wiring for shorts to ground between the switch and module. Repair damaged wiring or replace connectors as needed.
Check related fuses, relays, and intermediate connectors for continuity and correct operation. Replace any failed components.
If wiring and switch check good, consider replacing the service-disconnect sensor/switch or HV junction connector. Retest after repair.
If problem persists after wiring and component replacement, suspect controller input circuit fault; consult factory procedures for module testing/repair or replacement.
Clear DTCs, perform functional tests and road/operate test to confirm the HV system operates normally and code does not return.

Likely causes

Disconnected service disconnect plug or safety interlock left open
Damaged cable insulation or chafed wiring shorting to chassis ground
Corroded or water-intruded connector at the service disconnect or HV junction box
Failed service-disconnect switch/sensor (contacts worn or broken)
Missing/failed fuse or HV interlock device preventing correct signal

Fault status

⚠️ Status

Controller reports LOW signal on the High Voltage Service Disconnect circuit (service disconnect open, short to ground, or circuit fault). HV system may be disabled for safety.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours