This Cummins ISB fault code document covers Fault Code 123 for the intake manifold pressure sensor circuit on Cummins ISB CM550 engines. It identifies PID P102, SPN 102, FMI 4 and gives a step-by-step diagnostic path for checking sensor supply voltage, signal voltage, harness condition, ECM connector pins, and final code clearing. The file is a 6-page English PDF intended for service diagnosis, not a general operation manual.
Official Cummins ISB fault code document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; intake manifold pressure sensor circuit |
| Publication no. | Not shown in extract |
| Year/Revision | Unknown; document page footer shows Copywrite 2017 |
| Pages | 6 |
| File size | 0.6 MB |
| Format | |
| Language | English |
Document table of contents
- Fault Code: 123
- PID: P102
- SPN: 102
- FMI: 4
- Intake Manifold Pressure Sensor Circuit
- Description
- Component Location
- Troubleshooting Steps
- Step 1A: Turn key switch ON and read the fault codes using the diagnostic tool
- Step 2A: Check for positive intake manifold pressure using a mechanical gauge
- Step 3A: Inspect the sensor circuit for tampering
- Step 3B: Inspect the intake manifold pressure sensor connector
- Step 3C: Check the intake manifold pressure supply voltage
- Step 3D: Check the intake manifold pressure signal voltage
- Step 4A: Inspect the engine harness and the ECM connector pins
- Step 4B: Check for an open circuit
- Step 4C: Check for a short circuit to ground
- Step 4D: Check for a short circuit from pin to pin
- Step 5A: Disable the fault code and verify that Fault Code 123 is inactive
- Step 5B: Clear the inactive fault codes
Applicable truck models
This document applies to Cummins ISB CM550 engines listed under the 1990-94 DTC group. The extract does not name specific truck makes or chassis models, so coverage should be matched by engine family and electronic control module application before use. It also references ISC Engines, Bulletin Number 3666245, only for a related base engine malfunction direction when low intake manifold pressure is found. For manufacturer information, visit Cummins official website.
Who needs this Cummins ISB fault code manual
Mechanics, fleet technicians, and workshop owners need this Cummins ISB fault code manual when diagnosing Fault Code 123, especially when checking intake manifold pressure sensor wiring, connector pins, sensor voltage, ECM harness continuity, or remaining active fault codes. It is useful when a diagnostic tool reports PID P102, SPN 102, FMI 4 and the repair must be verified after reconnecting components.
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