Network, generic

U0325 Software Incompatibility With Auxiliary Heater Control Module

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The auxiliary heater control module runs an extra heat source: a fuel-burning or electric coolant heater, or on electrified cars a high-voltage heater that warms the cabin while the engine is off. U0325 means a connected module rejects this unit's software. No manufacturer documents U0325 publicly. GM's 2013–2014 Volt shows the role: its coolant heater control module provides cabin heat in electric mode, and without it heat only comes once the engine runs (PIC5943). BMW shows that heater software can reach into OBD: on i3 and i8 the MIL came on with fault 8013A3, a low reading of the high-voltage heater's OBD coolant temperature sensor, although heating worked; BMW blamed the climate control software and reprogrammed the car (SI B12 21 16). U0166 is lost contact, U0425 invalid data. Expect missing heat.

Likely causes

Heater unit or its controller replaced without programming or coding
Climate or vehicle software level does not match the heater variant
Retrofitted parking heater not coded into the vehicle network

Symptoms

  • No auxiliary or parking heat, cabin warms only with the engine running
  • Heater warning or service message
  • On plug-in hybrids the engine starts more often for heat

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€60–700
Time0.5–2 h

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

Parts involved

auxiliary heatercontrol module software

Related codes

U0166U0425U0324

References: static.nhtsa.gov, static.nhtsa.gov.