Cummins ISM code 1878 is the Cummins ISM CM871 (2007-09) diagnostic reference for fault code 1878, the aftertreatment diesel particulate filter outlet temperature sensor DTC that signals that the diesel particulate filter outlet temperature reading is erratic, intermittent, or incorrect. This 5-page PDF from the Cummins ISX and ISM Troubleshooting and Repair documentation lists the fault identifiers, component description, and step-by-step checks. It carries PID S328, SPN 3245, FMI 2/2, and lights Amber warning lamp.
Official document details
| Brand | Cummins |
| Model coverage | ISM CM871 (2007-09) and ISX CM871 engines |
| System / group | ISM CM871 (2007-09) / DTCs |
| Fault code | 1878 — SPN 3245, FMI 2/2, PID S328 |
| Warning lamp | AMBER |
| Pages | 5 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (PID, SPN, FMI, warning lamp)
- Description
- Shop Talk
- Component location
- Troubleshooting steps
Cummins ISM code 1878 diagnosis
Fault code 1878 signals that the diesel particulate filter outlet temperature reading is erratic, intermittent, or incorrect. The aftertreatment temperature sensors are thermistors that change resistance with exhaust temperature; the ECM supplies a 5-volt reference and converts the returned signal voltage into a temperature value. According to the Cummins Shop Talk guidance, technicians should first verify that the ECM calibration is correct and recalibrate if necessary before component replacement. Possible causes listed in the document include:
- A stuck in-range aftertreatment diesel particulate filter outlet temperature sensor.
- High resistance in the sensor signal or return wires.
Applicable truck models and engines
This document applies to Cummins ISM CM871 (2007-09) engines and the closely related ISX CM871 platform used in on-highway trucks, so it suits heavy-duty tractors and vocational trucks fitted with these engines and their aftertreatment systems. Always confirm the engine dataplate and refer to the OEM troubleshooting and repair manual for chassis-specific pin numbers. Full specifications are published on the Cummins official website.
Who needs this Cummins ISM code 1878 manual
Diesel technicians, fleet mechanics, and workshop owners diagnosing the aftertreatment diesel particulate filter outlet temperature sensor on ISM CM871 engines will use this reference to read the fault identifiers correctly and follow the factory test sequence for code 1878.
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