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DTC codes / P0Cxx · Hybrid propulsion / P0C38

P0C38DC/DC Converter Temperature Sensor A Circuit

P0C38 indicates that the powertrain control module has detected an abnormal condition in the temperature sensor circuit for the DC/DC converter, which is the component that steps high-voltage battery power down to charge the 12-volt system. The computer monitors the sensor's signal for expected voltage or resistance behavior and sets this code when the reading falls outside the calibrated range or the circuit fails a rationality check.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the check engine light or service vehicle soon message, often with no other symptoms
  • Reduced or disabled DC/DC converter output, leading to a low 12-volt battery and dimming lights
  • The vehicle may enter a reduced-power or limp mode to protect the converter from overheating
  • A warning message on the dash indicating a charging system or high-voltage system fault
  • In rare cases, the converter may shut down completely, causing the 12-volt system to run only on the battery until it drains

Common causes, most likely first

  1. Faulty DC/DC converter temperature sensor, either open circuit, short circuit, or skewed resistance
  2. Damaged or corroded wiring harness or connector at the sensor or converter assembly
  3. Poor electrical connection at the converter, such as loose ground or pin fit issues
  4. Failed DC/DC converter internal electronics affecting the sensor signal
  5. Powertrain control module software error or internal fault in the temperature sensing circuit
  6. Overheating of the converter due to a separate cooling system fault, which can damage the sensor

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the high-voltage and charging systems
  2. Inspect the sensor wiring and connector for damage, corrosion, or loose pins, and repair as needed
  3. Measure the resistance of the temperature sensor at ambient temperature and compare to the manufacturer's specification
  4. Backprobe the sensor signal circuit at the control module and compare the voltage to the expected range for the current temperature
  5. Check the converter's cooling system and ensure there are no restrictions or coolant flow issues causing overheating
  6. If the sensor is faulty, replace it according to service information, which may require removing the converter assembly
  7. Clear the code and perform a road test to confirm the repair, monitoring the sensor data to ensure it reads correctly

What the DC/DC temperature sensor code hides

  • A common oversight is replacing the DC/DC converter when only the temperature sensor is faulty, so always test the sensor and its circuit before condemning the converter.
  • The code can be set by a momentary glitch in the signal, so check for intermittent wiring issues by wiggle-testing the harness while watching live data.
  • On many hybrids and electric vehicles, the DC/DC converter temperature sensor shares a circuit with other sensors, so a fault in a related sensor can trigger this code.
  • A low 12-volt battery can cause the converter to work harder and overheat, so always check the 12-volt battery condition and charging system as part of the diagnosis.
  • Some vehicles require a software update to the control module to correct overly sensitive temperature sensor rationality thresholds.

Can I keep driving with P0C38?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy electrical loads and long trips because a failing converter can drain the 12-volt battery and leave you stranded. If the vehicle enters limp mode or the battery warning light illuminates, stop driving and seek professional assistance.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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