CLAAS 772Bh – ECU: Low Engine Coolant Temperature Input Voltage

The engine control module (Eng A15) has detected an abnormally low voltage signal from the engine coolant temperature sensor (B45). This condition typically indicates a short circuit to ground in the sensor's electrical circuit or an internal failure of the sensor itself. The ECU sends a 5V reference voltage to the thermistor sensor; a low voltage reading means the signal is being shorted to ground before returning to the ECU, which may affect the proper operation of the engine cooling system.

• Commandor
• Dominator
• Lexion
• Medion
• Mega
• 1450 CWS/WTS
• 1550 CWS/WTS
• W540
• W550
• T550
• T560
• Jaguar
• Axion
• Celtis
• Telehandlers

1. 1

   Check engine coolant level and condition to ensure low coolant or air pockets are not causing incorrect sensor readings

2. 2

   Visually inspect the ECT sensor's wiring harness and connector for damage, corrosion, loose connections, or a signal wire shorting to ground

3. 3

   Test the electrical circuit by disconnecting the sensor and checking for a 5-volt reference signal from the ECU and continuity on the ground circuit to the chassis. If the reference voltage is 0V, it may indicate a short circuit in the wiring or a problem with the ECU's power supply

4. 4

   Test the ECT sensor resistance using a multimeter to verify it changes inversely with temperature (NTC type). An open circuit or zero resistance indicates a faulty sensor

1. 1

   Locate the ECT sensor

   Find the sensor screwed into a coolant passage near the thermostat housing or directly into the cylinder head. It will have an electrical connector with two or three wires.

2. 2

   Disconnect and remove the sensor

   Disconnect the negative battery terminal. Place a drain pan underneath to catch spilled coolant, unplug the electrical connector, and carefully unscrew the old sensor using a deep socket or wrench.

3. 3

   Install the new sensor

   Clean the threaded area on the engine block. Apply a small amount of thread sealant if not pre-applied, screw the new sensor in by hand to prevent cross-threading, and tighten gently with a wrench. Do not overtighten.

4. 4

   Finalize the repair

   Reconnect the electrical connector and negative battery terminal. Top off the engine coolant to the correct level, bleed any air from the system, start the engine to check for leaks, and use a diagnostic tool to clear the fault code.