Powertrain, generic · Hybrid propulsion

P0D79 A/C Compressor Control Module Output Driver Temperature Sensor Circuit Intermittent/Erratic

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P0D79 marks an erratic signal from the output driver temperature sensor, the sensor that guards the compressor's power transistors: values flicker or drop out briefly instead of staying wrong. No manufacturer publishes set criteria. GM's 2019 Volt table lists P0D79 next to P0D77 and P0D78 as an IGBT-sensor circuit fault that suspends the plausibility checks, which shows the code is in use, but without thresholds. A Hyundai patent on temperature sensors for power switches names loose connectors, electrical noise, board defects and cold solder joints as typical origins of such unstable readings. Because the compressor can no longer trust its overheat protection, it may cut out repeatedly. CARB requires thermal-management inputs to be checked for circuit faults.

Likely causes

Cold or cracked solder joint at the IGBT sensor
Loose low-voltage connector or ground at the compressor
Switching noise from the inverter coupling into the sensor signal

Symptoms

  • Air conditioning cuts out repeatedly
  • Code appears sporadically

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€50–2,500
Time0.5–5 h

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

Parts involved

ac compressor cm output driver temp sensorac compressor module

Related codes

P0D75P0D76P0D77P0D78P0D74

References: law.cornell.edu, gsi.ext.gm.com, patents.google.com.