Powertrain, generic · Hybrid propulsion

P0B34 High Voltage Service Disconnect Circuit Performance

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B34 covers a plausibility fault of the service disconnect detection: the signal is electrically within limits but does not match what the controller expects, for example a plug reported as removed while the high-voltage bus still shows voltage, or a state that changes without a matching event. Audi lists P0B3400 in the controller at address 008C of the 2025 Q5 e-hybrid, together with U029A00 and U059B00, and asks technicians to log the case in its pending service database; no threshold is published. CARB requires hybrid components to be checked for rationality as input devices. Pure circuit, low, high and open faults are P0B33, P0B35, P0B36 and P0B37. The car may refuse ready mode or charging.

Likely causes

Battery controller software fault (Audi case under investigation)
Loose plug or worn contacts giving an implausible detection state
Increased resistance in the detection loop
Communication fault between battery controller and other modules

Symptoms

  • Electrical system or high-voltage warning
  • No ready mode or charging interrupted
  • Related network codes stored at the same time

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–1,500
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hv service disconnect switchwiring harnessbms

Related codes

P0B33P0B35P0B36P0B37P0A0B

References: static.nhtsa.gov, law.cornell.edu, patents.google.com.