CM850 Electronic Control System – FAULT CODE 1851

Exhaust Gas Temperature 2 — Abnormal Rate of Change


Fault Code: 1851
SPN: 3249
FMI: 10
LAMP: Amber

Exhaust Gas Temperature 2 — Abnormal Rate of Change. The catalyst outlet temperature sensor is not responding to a change in engine operating conditions.

Default temperature value used for catalyst outlet temperature.

Circuit: Exhaust Gas Temperature 2

Circuit Description

The exhaust gas temperature #2 sensor is used by the electronic control module (ECM) to monitor the engine exhaust temperature entering the catalyst unit. The ECM monitors the voltage on the signal pin and converts this to a temperature value.

Component Location

The catalyst inlet temperature #2 sensor is located in the aftertreatment system. It is located between the turbocharger exhaust and the catalyst unit exhaust in the exhaust system.

Shop Talk

The exhaust gas temperature #2 is monitored during engine warm-up. If the exhaust gas temperature 2 reading is not changing to match the engine operating conditions, the exhaust gas temperature 2 sensor is then determined to be stuck in-range and this fault code is logged. The ECM must not see engine speed for a period of eight hours before this diagnostic will run.

Possible causes of this fault code include:

  • Stuck in-range exhaust gas temperature #2 sensor reading
  • High resistance in the exhaust gas temperature #2 sensor signal or return lines.

On-Board Diagnostics (OBD) Information (Euro 4 and 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.
  • The ECM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. The MIL lamp and fault code can also be cleared using the INSITE™ service tool.
  • The fault code will be cleared from memory after 40 consecutive drive cycles where the diagnostic runs and passes.

Refer to Troubleshooting Fault Code t05-1851

Last Modified:  08-Jul-2010