From Ross-Tech Wiki

18613/P2181/008577 - Performance Malfunction in Cooling System

Possible Symptoms

  • Malfunction Indicator Light (MIL) ON
  • Reduced Heater Output - Cold toes
  • Incorrect Temperature Gauge Readings
  • Increased Emissions

Possible Causes

  • Faulty Coolant Sensor
  • Faulty Coolant Thermostat
  • Faulty Wiring, Connections

Note: This fault code sets when engine coolant temperature mapping is lower and out of expected range based on operating conditions of the engine.

  • For example: Engine warms up, thermostat opens and stays open, coolant temperature drops below normal operating range. The ECM knows the coolant temperature should stay within 80.0...110.0 °C typically after warm up. Thus a drop in coolant temperature below normal operating temperature is not possible without a Malfunction in Cooling System.

Possible Solutions

  • Check G62 - Engine Coolant Temperature Sender
    • Inspect wiring for G62 (Coolant Migration, damage, corrosion, etc)
  • Check (if applicable) G83 - Radiator Outlet, Coolant Temperature Sender
    • Inspect wiring for G83 (Coolant Migration, damage, corrosion, etc)
  • Check Coolant Thermostat
    • Use Graph function in VCDS, Measuring Value Blocks - MVB
    • Start Engine cold, graph Coolant Temperature Sender (G62) Typically MVB Group-001
    • Hold RPM around 1,500rpm and watch coolant temp increase in Graph until thermostat opens, indicated by a slight drop in coolant temp
    • If coolant temp drops below minimum operating temperature (80°C) or never reaches operating temperature, (verified by external thermometer) suspect failed thermostat
  • Vehicles with both G62-Engine Outlet, Coolant Temperature Sensor and G83-Radiator Outlet, Coolant Temperature Sensor
    • Use Measuring Value Block group MVB-130 instead on MVB-001
    • G62 should increase in Temperature before G83 increase when engine coolant is cold
    • G83 will increase when the thermostat opens and after G62 reaches operating temperature (80°C)
    • If G62 and G83 both increase while engine warms up, suspect failed thermostat

Special Notes

  • Check the stored Freeze Frame data with this fault code. Freeze Frame information will be found in the fault code description (if the module supports it) or in Generic OBD-II if the vehicle complies with those regulations.
    • Freeze Frame data stored at -40*C is generally an indication of a faulty ECT or wiring.
    • Freeze Frame data stored at +140*C is generally an indication of a faulty ECT or wiring.
    • Freeze Frame data stored with in the 68*C ~ 80*C range is an indication that the vehicle was close to, but not within, the cooling systems normal operation range. The Thermostat itself or Cooling system components may be at fault.