P1A90: How to Diagnose & Fix — DC/DC Converter Input Voltage Sensor Fault (ICCU)
3 vehicles · 2 makes
How to diagnose and fix P1A90: 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.
Genesis GV70 · 2023–2025
The Integrated Charging Control Unit (ICCU) manages charging of the high-voltage pack and the 12V battery that runs accessories and control modules. The ICCU (and its internal fuse) can become damaged and stop charging the 12V system. The car then enters a fail-safe mode with warning lights, audible alerts, and reduced power; if driving continues it can fully lose drive power, sometimes preceded by an audible 'pop.' Drivers typically have ~22-45 minutes to pull over, with steering and brakes still functional. Genesis covered this under recalls tied to NHTSA 24V-204, expanded/replaced by Genesis 025G (Dec 2024), part of the broad Hyundai/Kia/Genesis ICCU campaign. The failed ICCU also produces dead-12V 'bricked' no-start events.
Common Symptoms
- Loss of drive power / reduced propulsion while driving
- Audible 'pop' then warning lights and alarms
- Repeated dead 12V battery / no-start ('bricked')
- Vehicle fails to DC fast charge or AC charge
- Check electric vehicle system warning
How to Fix
Verify the VIN against the ICCU recalls (Genesis 025G; NHTSA 24V-204 and its expansions). Dealers inspect and replace the ICCU and its fuse as necessary and apply updated ICCU software, free of charge. If you experience warning lights plus a power-reduction message, pull over and arrange transport rather than continuing to drive. A repeat dead-12V battery on an Electrified GV70 should trigger an ICCU diagnosis, not just a battery swap.
Sources for this issue (1)
Hyundai Ioniq 5 · 2022–2024
The Integrated Charging Control Unit (ICCU), which houses the DC-to-DC converter that keeps the 12V battery charged from the high-voltage pack, can suffer overvoltage and thermal overload that blows its internal 12V-feed fuse. When it fails the car may refuse to DC fast charge, charge slowly, drop into reduced-power 'turtle mode' on the highway, or lose all motive power and need a tow. NHTSA recall 24V-204 (March 2024, ~99K vehicles) was followed by a January 2025 expansion covering ~145K vehicles after failures recurred on remedied cars.
Common Symptoms
- Sudden loss of drive power / 'turtle mode' warning while driving
- Repeated dead 12V battery / car won't power on or boot
- Vehicle won't DC fast charge or charges far slower than rated
- Loud popping/bang from front during charging followed by warning lights
- Car stranded and requires a tow out of limp-home mode
How to Fix
Covered by NHTSA recall: dealers check for DTC P1A9096 — if absent they apply an ICCU software update to reduce overvoltage stress; if present they replace the ICCU and its fuse, flush/refill coolant, and install updated software, free of charge. Owners reporting recurrence after the software-only fix have driven ongoing litigation and the January 2025 follow-up campaign.
Sources for this issue (3)
Hyundai Ioniq 6 · 2023–2025
NHTSA recall 24V-868 covers 28,932 model-year 2023-2025 Ioniq 6 vehicles. Electrical load conditions can cause a MOSFET inside the Integrated Charging Control Unit (ICCU) to fail and open the ICCU fuse, preventing the ICCU from charging the 12-volt battery. The vehicle then enters a fail-safe mode that gradually reduces motive power; if the 12-volt battery is fully depleted, all motive power can be lost.
Common Symptoms
- Dashboard warning lights or warning messages
- Audible warning chime
- Gradual reduction in motive power or speed
- Loss of motive power after full 12-volt battery depletion
How to Fix
Check the VIN for NHTSA recall 24V-868 (Hyundai 272), which expands and replaces the earlier recall. Hyundai dealers update ICCU software and replace the ICCU assembly and associated fuse if necessary, free of charge. Vehicles repaired under the earlier campaign still need the updated remedy.
Sources for this issue (1)
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Frequently asked questions
What does P1A90 mean?
P1A90 stands for "DC/DC Converter Input Voltage Sensor Fault (ICCU)." Stored by the Integrated Charging Control Unit, which bundles the on-board charger, DC-DC converter, and vehicle-to-load export hardware into one box. The module reports an implausible or out-of-range input-voltage sensor reading on the DC-DC converter stage, meaning the ICCU can no longer reliably step the high-voltage pack down to charge the 12-volt battery. Hyundai/Kia/Genesis service documentation carries it as the sub-coded fault P1A9096 in the ICCU inspection, fuse-replacement, and software-update campaign. Once the ICCU stops feeding 12 volts, the 12V battery drains and the vehicle progressively loses accessories, then drive power.
What are the most common causes of P1A90?
The most common causes of P1A90 are: ICCU internal failure (DC-DC converter stage) on E-GMP platform vehicles, Blown ICCU input fuse following an ICCU fault event, Outdated ICCU control software (addressed by manufacturer software update), 12-volt battery repeatedly deep-discharged by a failing ICCU. The specific cause varies by vehicle.
How much does it cost to fix P1A90?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by P1A90?
Au7o has documented P1A90 across 3 vehicle models from 2 manufacturers: Genesis, Hyundai.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.