Cummins ISM code 1242 is the Cummins ISM CM871 (2007-09) diagnostic reference for fault code 1242, the accelerator pedal position sensor DTC that is set when the accelerator pedal position sensor 1 and 2 signals are erratic, intermittent, or incorrect. 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 P091, SPN 91, FMI 2/2, and lights Red 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 | 1242 — SPN 91, FMI 2/2, PID P091 |
| Warning lamp | RED |
| Pages | 6 |
| 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 1242 diagnosis
Fault code 1242 is set when the accelerator pedal position sensor 1 and 2 signals are erratic, intermittent, or incorrect. The accelerator position sensor is a hall-effect sensor on the pedal that varies its signal voltage from low at 0 percent to high at 100 percent travel. The pedal carries two position sensors, both fed a 5-volt supply, and the signal voltage for accelerator position 1 is twice that of accelerator position 2. 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 signal that does not track correctly between the two pedal sensors.
- Wiring or connector faults on the accelerator pedal circuit.
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 1242 manual
Diesel technicians, fleet mechanics, and workshop owners diagnosing the accelerator pedal position sensor on ISM CM871 engines will use this reference to read the fault identifiers correctly and follow the factory test sequence for code 1242.
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