CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 238

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Overview

ISX – Engine Speed Sensor Supply 3 Circuit SMALL | MEDIUM | LARGE

ISM – Engine Speed Sensor Supply 3 Circuit SMALL | MEDIUM | LARGE

Circuit Description

The sensor supply 3 circuit provides 5 volt supply to the primary engine speed/position sensor.

Component Location

The engine speed sensor is located in the lower portion of the front cover on the intake side of the engine. 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 or when the engine is running.

Conditions for Setting the Fault Codes

The electronic control module (ECM) detects that the sensor supply 3 signal voltage is less than 4.8-VDC for more than 1 second.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The backup engine speed sensor will be used by the ECM for the engine speed signal.

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 ECM monitors the voltage level on the engine speed sensor +5 volt supply circuit. If the voltage falls below a limit which can be calibrated then this fault is recorded.

Possible causes of this fault code are a short circuit to ground in the engine harness, sensor, or ECM.

Refer to Troubleshooting Fault Code t05-238