Cummins ISM code 1666 is the Cummins ISM CM871 (2007-09) diagnostic reference for fault code 1666, the aftertreatment diesel oxidation catalyst inlet temperature sensor DTC that is set when the exhaust gas temperature 1 circuit reads above normal or shorts to a high source. This 6-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 S326, SPN 3241, FMI 3/3, 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 | 1666 — SPN 3241, FMI 3/3, PID S326 |
| Warning lamp | AMBER |
| Pages | 6 |
| File size | 0.3 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 1666 diagnosis
Fault code 1666 is set when the exhaust gas temperature 1 circuit reads above normal or shorts to a high source. The thermistor sensor changes resistance with temperature and the ECM converts the signal voltage into a temperature value. The diesel oxidation catalyst inlet temperature sensor shares return wires in the OEM harness with other sensors, so a shorted return can make several codes active. 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:
- An open in the signal circuit.
- A signal wire shorted to a high source.
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 1666 manual
Diesel technicians, fleet mechanics, and workshop owners diagnosing the aftertreatment diesel oxidation catalyst inlet temperature sensor on ISM CM871 engines will use this reference to read the fault identifiers correctly and follow the factory test sequence for code 1666.
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