Fault Family
System: Powertrain (P-Codes)
3 SAE Codes
HV Battery Power Off Circuit
Diagnostic & Technical Explanation
Code P0A27 sets when the low-voltage relay the BMS uses to confirm and command the pack's fully de-energized state does not report the state the control module expects — this is a status/interlock relay, not one of the main HV contactors that carry pack current. The most common physical causes are a corroded or unseated connector on the relay's 12V control side, chafed control-circuit wiring between the BMS and the relay, and a relay coil or contact that has failed internally. Because this circuit only reports pack disconnect status rather than switching HV current itself, diagnosing its low-voltage side does not require opening the HV bus, though any repair that touches the relay's HV-side contacts does.
These 3 diagnostic trouble codes share one
detection mechanism and one repair path, which is why MechanicDB groups them into a single
authored fault family rather than repeating the same explanation 3 times.
What this page does not show
This page publishes the fault mechanism and the code index. The licensed dataset adds, for
every one of the 15,886 codes, the full authored repair set (56,729 procedures in total)
with the fields deliberately withheld here:
- Procedures 2..n after the first-listed procedure
- Aftermarket parts cost ranges in USD (
est_parts_cost_min/max_usd)
- Professional labor-hour estimates (
est_labor_hours)
- Step-by-step diagnostic and repair instructions
- Replacement-part mappings and catalog lookups
- 6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)