CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 187 (ISM)

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Overview

ISM – Sensor Supply 2 Circuit SMALL | MEDIUM | LARGE

Circuit Description

The sensor supply number 2 of the electronic control module (ECM) provides a 5-VDC SUPPLY sensor for the backup camshaft position sensor, exhaust gas pressure sensor, intake manifold pressure/temperature sensor, and the crankcase pressure sensor.

Component Location

Sensor supply number 2 is located in the ECM and provides a 5-VDC SUPPLY to various pressure sensors.

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 ECM detects that the sensor supply 2 signal voltage is less than 4.75-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.
• A default value is used for the exhaust gas pressure sensor, the intake manifold pressure sensor, and the crankcase pressure sensor.
• The backup camshaft position sensor will not be functional.

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.

Low voltage on the +5 volt supply line can be caused by a short circuit to ground in a supply line, a short circuit between a supply line and a return line, a failed sensor, or a failed ECM power supply.

During the fault code response test outlined for each sensor connected to sensor supply number 2, Fault Code 187 must be active before unplugging each sensor. If the fault code is not active, but can be easily duplicated by operating the engine, the following can be performed:

• Operate the engine under the conditions that will cause Fault Code 187 to become active, even if it logs for a short period of time, unplug one sensor at a time until Fault Code 187 stops logging under the test conditions. Each sensor can be unplugged with the engine running. Note: The engine may not start if the camshaft position sensor is unplugged.

Refer to Troubleshooting Fault Code t05-187