CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 691

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Overview

ISX – Turbocharger Compressor Inlet Temperature Sensor Circuit SMALL | MEDIUM | LARGE

ISM – Turbocharger Compressor Inlet Temperature Sensor Circuit SMALL | MEDIUM | LARGE

Circuit Description

The compressor inlet air temperature sensor is a variable resistor sensor and is used to measure the temperature of the air entering the compressor inlet of the turbocharger. The electronic control module (ECM) supplies 5 VDC to the compressor inlet temperature signal circuit. The ECM monitors the change in voltage caused by changes in the resistance of the sensor to determine the coolant temperature.

Component Location

The turbocharger compressor inlet air temperature sensor is located in the compressor casing of the turbocharger. Refer to Procedure 100-002 (Engine Diagrams) in Section E for a detailed component location view.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes

The ECM detects that the compressor inlet temperature signal voltage is greater than 4.8 VDC for more than one second.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• A default value for the compressor inlet temperature reading is used.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.

Shop Talk

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM. Refer to Procedure 019-032 (ECM Calibration Code) in Section 19 in the corresponding Troubleshooting and Repair Manual for the engine being serviced.

The turbocharger inlet air temperature sensor shares return wires in the engine harness with other sensors. An open return can cause multiple fault codes to be active. Before troubleshooting Fault Code 691, check for multiple fault codes. An extension harness between the main engine harness and the turbocharger compressor inlet temperature sensor can be used depending on the turbocharger arrangement.

Possible causes of this fault code:

• Open return circuit in the harness, connectors, or sensor.
• Open signal circuit or short circuit to a voltage source.
• Failed sensor.

The resistance of the sensor varies with temperature. The sensor resistance should conform to the values in the table shown below.

Refer to Troubleshooting Fault Code t05-691