Powertrain, generic · Hybrid propulsion

P0C79 Drive Motor A Inverter Voltage Too High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P0C79 reports that the DC voltage at the inverter of drive motor A rose above its protection limit. Overvoltage can come from regenerative energy the battery cannot absorb, from a contactor opening under load or a loose high-voltage connection, and it can also be a false reading. In the 2018 Outlander PHEV a hardware comparator in the front motor control unit trips at 370 V; one event with the IGBTs active, or 0.5 s with them shut down, sets the code; after ruling out other voltage codes, the manual checks the torque of the battery cable at the power drive unit. Subaru revised its diagnosis for the 2014-2015 Crosstrek Hybrid (16-114-18), and Audi traces intermittent P0C7900 on the Q4 e-tron to software. Drive motor B uses P0C7A, the generator P0C7B.

Likely causes

Battery cable at the inverter loose or not at specified torque
Inverter or its voltage detection faulty
Voltage spike from regeneration or a contactor opening under load
Motor control software, fixed by an update

Symptoms

  • Hybrid or EV warning lamp, electrical system fault message
  • Drive system will not activate or shuts down until restarted
  • Reduced drive power

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–4,000
Time0.5–6 h

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

Parts involved

drive motor a inverterdc link capacitor

Related codes

P0C7AP0C7BP0A78P0D2E

References: mitsubishitechinfo.com, static.nhtsa.gov, static.nhtsa.gov, mitsubishitechinfo.com.