P0D78: A/C Compressor Control Module Output Driver Temperature Sensor Circuit Low

P0D78 is set when the output driver (IGBT) temperature sensor of the electric A/C compressor signals low, which for an NTC sensor means an implausibly hot value. GM uses 274 °C or more in the 2011–2015 Volt and the 2016 ELR, and above 150 °C in the 2016–2019 Volt; detection takes 30 of 60 samples at 50 ms, 40 of 50 at 100 ms or 4 of 5 s, Type B with MIL after two trips. Temperatures like these are beyond what the power stage survives, so a shorted sensor is more likely than real heat, although a seized compressor or a failed condenser fan can drive the IGBTs hot. Expect the A/C to switch off. The cold-side counterpart is P0D77, plausibility P0D76.

Symptoms

• Check engine light after two trips
• Air conditioning switched off

Most likely causes

• Short circuit in the IGBT temperature sensor path
• Real overheating of the power stage from high load or poor condenser cooling
• Faulty value transmission to the host controller

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery and grounds
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Clear the code and see if it returns
4. If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
5. Check whether a software update is available
6. Do not replace the control module without a full diagnosis

What each character of P0D78 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• D: Subsystem depends on the code range
• 78: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0D78?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P0D78?

The most common causes are: short circuit in the IGBT temperature sensor path; real overheating of the power stage from high load or poor condenser cooling; faulty value transmission to the host controller.

Related codes

• P0D77A/C Compressor Control Module Output Driver Temperature Sensor Circuit High
• P0D76A/C Compressor Control Module Output Driver Temperature Sensor Performance
• P0D75A/C Compressor Control Module Output Driver Temperature Sensor Circuit
• P0D79A/C Compressor Control Module Output Driver Temperature Sensor Circuit Intermittent/Erratic
• P0D73A/C Compressor Control Module Internal Temperature Sensor A Circuit Low

Sources

• gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
• gsi.ext.gm.com: 16OBDG01 Hybrid Diagnostics
• gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.