CM850 Electronic Control System – FAULT CODE 334

Engine Coolant Temperature – Data Erratic, Intermittent, or Incorrect


Fault Code: 334
PID: P110
SPN: 110
FMI: 2
LAMP: Amber

Engine Coolant Temperature – Data Erratic, Intermittent, or Incorrect. The engine coolant temperature reading is not changed with engine operating conditions.

The ECM will estimate engine coolant temperature.

Engine Coolant Temperature Sensor

Circuit Description

The engine coolant temperature sensor is used by the electronic control module (ECM) to monitor the engine coolant temperature. The ECM monitors the voltage on the signal pin and converts this to a temperature value. The engine coolant temperature value is use by the ECM for the engine protection system and engine emission control.

Component Location

The engine coolant temperature sensor is located on the thermostat housing. Refer to Procedure 100-002 for a detailed component location view.

Shop Talk

Two different failure modes of the engine coolant temperature sensor can trigger this fault code. The engine must be turned off for period of 8 hours before this diagnostic will run. When the keyswitch is turned ON after an 8 hour cold soak, engine coolant temperature is compared to intake manifold temperature. If coolant temperature is found to be higher than intake manifold temperature by a calibratable value, the fault code is logged. The diagnostic also checks to make sure that coolant temperature increases during the first 10 minutes of engine operation. If coolant temperature does not increase by a calibratable value, this fault code is logged.

Possible causes of this fault code include:

  • Stuck in-range engine coolant temperature sensor.
  • High resistance in the engine coolant temperature sensor signal or return lines.

On-Board Diagnostics (OBD) Information (Euro 4 Stage 1+ Certified Engines):

  • The ECM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
  • An engine torque derate will be activated after 50 hours of engine operation with the fault code active.
  • The ECM turns OFF the malfunction indicator lamp (MIL) after 1 ignition cycle that the diagnostic runs and does not fail. The MIL lamp cannot be cleared using the INSITE™ service tool.
  • The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

Refer to Troubleshooting Fault Code t05-334

Last Modified:  08-Jul-2010