CM850 Electronic Control System – FAULT CODE 1679

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Overview

Circuit: Catalyst Solution Temperature Sensor SMALL | MEDIUM | LARGE

Circuit Description

The catalyst solution temperature sensor is used by the electronic control module (ECM) to monitor the temperature of the catalyst solution in the catalyst tank. The ECM monitors the voltage on the signal pin and converts this to a temperature value.

Component Location

The catalyst solution temperature sensor is located in the catalyst tank. The tank is OEM mounted. For more information, contact the OEM service manual.

Shop Talk

This diagnostic runs when the engine has not been running for at least eight hours. The catalyst solution temperature sensor is compared to engine coolant temperature and intake manifold temperature when the key is turned on after the extended eight hour shutdown. This fault code is logged if the reading from the catalyst solution temperature sensor does not match the readings from engine coolant temperature and intake manifold temperature.

Possible causes of this fault code include:

• Stuck in-range catalyst solution temperature sensor
• High resistance in the catalyst solution temperature 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 t05-1679