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DTC codes / P0Dxx · Hybrid propulsion / P0D78

P0D78A/C Compressor Control Module Output Driver Temperature Sensor Circuit Low

P0D78 indicates that the air conditioning (A/C) compressor control module has detected a low voltage condition on the internal temperature sensor circuit that monitors the output driver stage. The module uses this sensor to protect the driver from overheating, and a low signal tells the module that the driver temperature is abnormally low or the circuit is shorted to ground.

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

Symptoms you may notice

  • The A/C compressor may stop engaging, resulting in no cold air from the vents.
  • A warning light on the dashboard, often the A/C or check engine light, may illuminate.
  • The climate control system may default to a fail-safe mode, such as blowing only outside air.
  • In some vehicles, the compressor may run continuously or cycle rapidly, though this is less common.
  • Often no symptoms besides the warning light, especially if the module still operates within safe limits.

Common causes, most likely first

  1. A short to ground in the wiring harness between the temperature sensor and the control module.
  2. A faulty temperature sensor with an internal short to ground.
  3. Corrosion or water intrusion at the sensor connector or module connector.
  4. A defective A/C compressor control module, particularly a failed internal driver or sensor interface.
  5. Damaged or pinched wiring from road debris or improper previous repairs.
  6. Poor ground connection for the control module or sensor circuit.

How to diagnose and fix it

  1. Use a scan tool to retrieve the code and verify that P0D78 is current, then check for any related codes in the A/C control module.
  2. Inspect the wiring harness and connectors at the A/C compressor control module and temperature sensor for signs of chafing, corrosion, or loose pins.
  3. Measure the resistance of the temperature sensor and compare it to the manufacturer's specification to rule out a faulty sensor.
  4. Backprobe the sensor signal circuit at the module connector and check for a short to ground with a multimeter while wiggling the harness.
  5. If the circuit tests normal, substitute a known-good control module or sensor, if possible, to confirm the fault before replacement.
  6. Repair any damaged wiring or connectors, clear the code, and road test the vehicle with the A/C on to verify the repair.
  7. If the module is defective, replace and reprogram it according to the manufacturer's procedure, then perform a system calibration if required.

Don't overlook the wiring harness

  • A low signal code is often caused by a short to ground in the harness rather than a failed sensor, so a thorough visual inspection of the entire circuit is essential.
  • The temperature sensor is frequently integrated into the control module and not serviceable separately, which can make diagnosis more challenging.
  • Water intrusion into the compressor control module connector is a common cause on vehicles that operate in wet or humid climates.
  • A weak or corroded ground connection for the module can mimic a sensor circuit fault, so always check ground points before condemning parts.
  • This code does not always mean the compressor is failing; the module may still function, but the protection strategy could be compromised.

Can I keep driving with P0D78?

You can usually continue driving with this code because the A/C system may simply be disabled, but avoid using the A/C until the fault is repaired to prevent potential compressor damage. If the compressor is engaged and making unusual noises, stop using the A/C and seek service promptly.

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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