The ISM code 123 DTCs manual is a 7-page PDF that documents fault code 123, the intake manifold 1 pressure sensor circuit fault set for voltage below normal or shorted to low source. It explains how the ECM supplies 5 volts to the intake manifold pressure sensor and reads a signal that changes with intake manifold pressure during idle, deceleration and high load. The procedure is credited to TruckFaultCodes.com and covers the circuit description, component location and full troubleshooting steps.
Official document details
| Brand | Cummins |
| Model coverage | Cummins ISM CM871 and ISX CM871 (2007-09) engines |
| System / group | ISM CM871 (2007-09) / DTCs |
| Fault code | 123 (PID P102, SPN 102, FMI 4) |
| Pages | 7 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code 123 description
- Circuit description and ECM operation
- Component location
- Shop talk and possible causes
- Step-by-step troubleshooting flow
Applicable truck models
This diagnostic applies to Cummins ISM CM871 and ISX CM871 (2007-09) engines. The intake manifold pressure sensor is located in the air intake horn and shares supply and return wires with other sensors, so several codes can be active together. Possible causes include the signal circuit being open or shorted to ground in the harness or sensor, or the supply line being open or shorted to ground. For engine data and authorised service, visit the Cummins official website.
Who needs this ISM code 123 DTCs manual
Heavy-duty diesel technicians, fleet workshops and owner-operators reach for this manual when fault code 123 is logged. It gives the ordered checks and voltage measurements a technician needs to confirm whether the sensor, harness or ECM is causing the low-voltage reading.
Download the code 123 DTCs PDF
The complete procedure, wiring detail and step tables are available in the DiagTechPro manuals library; a free account is required to download the PDF. Keep it alongside the related ISM CM871 fault-code sheets listed below.
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