P0A0D: How to Diagnose & Fix — High Voltage System Interlock Circuit High
2 vehicles · 2 makes · $200-$3,000 repair
How to diagnose and fix P0A0D: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
BMW i8 · 2014–2020
The BMW i8's hybrid architecture creates complex interactions between the 12V auxiliary system and the high-voltage (HV) system. The 12V battery drains when the vehicle sits for extended periods, and unlike a simple ICE car, a dead 12V on the i8 prevents all HV system access - the car cannot charge, start, or drive. A critical but obscure failure mode involves a small safety connector wire under the red 12V battery terminal cover that acts as a crash/rollover sensor to cut HV power. This wire is frequently accidentally disconnected during 12V battery replacement, causing the car to show "DRIVETRAIN NO RESTART" and refuse to charge or drive. The i8's complex data bus means a weak 12V battery causes cascading errors across all vehicle systems. The 12V system is charged by the DC/DC converter in the EME rather than a conventional alternator, and BMW SIB 61 08 16 covers i8s produced from October 1, 2015 with I-levels 15-11-501 through 16-03-503 whose DC/DC converter does not supply enough 12V power (CCM 213 'Battery is not charged', fault 22223F).
Common Symptoms
- "DRIVETRAIN NO RESTART" warning on dashboard
- Vehicle won't charge
- Vehicle won't start or enter Drive Ready mode
- Multiple cascading error messages on startup
- HV battery slowly discharges while vehicle sits
- Warning lights for systems that have no actual fault
- Remote functions (app) stop responding
- Battery discharging while stationary warning
How to Fix
For 12V battery replacement: Use BMW-spec AGM battery and ENSURE the small black safety wire under the red terminal cover is reconnected - this is the #1 cause of post-replacement "Drivetrain No Restart" errors. Register new battery via dealer ISTA tool. For HV battery discharge: If the HV battery fully depletes and 12V dies, the car may need dealer-level tools to restart the HV system. Preventive: Use a quality battery tender when vehicle will sit for more than 1 week. Check that all modules are sleeping properly (dealer can run a sleep current test). For DC/DC converter (12V charging) faults: the dealer checks the I-level and DC/DC converter output per SIB 61 08 16, programs the vehicle if the I-level is in the affected range, and replaces the EME if fault 22223F is present.
Sources for this issue (2)
Ford Focus · 2012–2018
On the battery-electric Focus, the high-voltage pack's main positive and negative contactors (relays) fail - either welding stuck closed or burning their contacts open. When a contactor faults, the on-board charger cannot close the HV circuit, so the car reports a charging fault, refuses to accept AC from either the 120V convenience cord or a 240V EVSE, and may throw HV isolation faults. Owners on the Focus Electric community have traced dead-charge conditions to burnt contactors in the upper pack, sometimes alongside coolant intrusion into the pack, and Ford also issued service information for HV packs that will not charge on the second-generation 120V charge cord.
Common Symptoms
- Vehicle will not charge on 120V or 240V
- Charge port light does not illuminate or flashes an error
- Stop Safely Now or high-voltage warning message
- Unlocking charge cord message on the display
- Loss of range or no propulsion
How to Fix
Diagnose with the HV pack DTCs before replacing the charge cord or the on-board charger - a stuck or open contactor sets specific battery energy control module codes. The repair is replacement of the affected contactor inside the HV battery pack, which requires a high-voltage-qualified technician (pack de-energizing, isolation testing, coolant loop handling). If the pack shows coolant intrusion, that leak must be repaired or the replacement contactor fails again. Also verify the EVSE and its charge-cord software level, since the factory second-generation 120V cord has its own no-charge service fix.
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Sources for this issue (3)
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P0A0D code reference
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Frequently asked questions
What does P0A0D mean?
P0A0D stands for "High Voltage System Interlock Circuit High." The high-voltage interlock circuit voltage is high (typically an open in the HVIL loop). An open interlock causes the HV system to disable for safety.
What are the most common causes of P0A0D?
The most common causes of P0A0D are: Open HV interlock loop (disconnected connector or service plug), Broken interlock wire, Corroded/damaged pins, Control module fault. The specific cause varies by vehicle.
How much does it cost to fix P0A0D?
Repair costs for P0A0D range from $200 to $3,000, depending on the vehicle and root cause.
Which vehicles are affected by P0A0D?
Au7o has documented P0A0D across 2 vehicle models from 2 manufacturers: BMW, Ford.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.