From Ross-Tech Wiki

P2556 - Engine Coolant Level Sensor/Switch: Electrical Malfunction

Possible Symptoms

  • MIL On
  • Cooling system malfunctioning

Possible Causes

  • Faulty Engine Coolant Level Sensor (G32)
  • Faulty Engine Temperature Control Actuator (N493)
  • Wiring or power/ground issues to those components

Possible Solutions

  • Check Engine Coolant Level Sensor (G32), Engine Temperature Control Actuator (N493) in addition to the related wiring per the repair manual.

Special Notes

  • At face value you would initially believe this DTC is for the Engine Coolant Level Sensor however in most cases that sensor is wired to the 17-Instrument Cluster or the 09-Central Electronics. The Coolant Level Sensor is not usually wired directly to the 01-Engine control module. In those cases the thermostat (N493) and the wiring to it should be checked as per post #8 in this thread: https://forums.ross-tech.com/index.php?threads/28967/
    • The example vehicle would use this generation 09-Cent. Elect. module MLB based Cent. Elect. (J519) BCM1 and measuring block group 028.1 can be used to check the Coolant Level (G32) status.