This 6-page PDF documents Cummins fault code 256, the ambient air temperature sensor circuit on the Cummins M11 and N14 CELECT Plus (1995-98) engine platform. Published in the TruckFaultCodes.com fault code library (© 2017), it carries the yellow lamp, PID P171, SPN 171 and FMI 4, and lays out the full factory troubleshooting tree.
Cummins fault code 256 document details
| Brand | Cummins |
| Model coverage | M11 and N14 CELECT Plus (1995-98) |
| System / group | Ambient Air Temperature Sensor Circuit — Fault Code 256 |
| Publication reference | Bulletin 3666130 (Troubleshooting and Repair Manual, Industrial CELECT Plus System) |
| Year / revision | 1995-98 platform, TruckFaultCodes.com 2017 edition |
| Pages | 6 |
| File size | 0.45 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification (PID P171, SPN 171, FMI 4, yellow lamp)
- Circuit description
- Component location
- Shop talk and sensor resistance table
- Troubleshooting steps 1A through 5B
- Multiple Fault Code Trees A and B
Circuit description and component location
The ambient air temperature sensor lets the ECM monitor outside air temperature for the Idle Shutdown Ambient Air Temperature Override feature. This code covers the sensor circuit itself, tested for shorts, opens and pin-to-pin faults across a six-page tree. The ambient air temperature sensor location is OEM dependent, so the OEM Troubleshooting and Repair Manual is referenced for its exact position.
The sensor resistance from pin A to pin B should read between 175 ohms and 244k ohms, and the resistance-versus-temperature table runs from about 30k to 60k ohms at 0 C down to 600 to 675 ohms at 100 C. All checks are made with a Cummins service tool such as Compulink, Echek or a diagnostic tool, and inactive codes are cleared once the repair is confirmed.
Applicable truck models and engines
This document applies to Cummins M11 and N14 CELECT Plus (1995-98) electronic engines and is filed under the CELECT Plus diagnostic trouble codes group, so it suits on-highway and industrial installations that run these engines. For engine specifications and dealer support, see the official Cummins support site at the Cummins engine support portal. The full PDF is part of the ambient air temperature sensor circuit chapter of the CELECT Plus fault code series held in the DiagTechPro manuals library.
Who needs this Cummins fault code 256 manual
Truck technicians and workshop owners need this document when a yellow lamp warns of a ambient air temperature sensor circuit problem on M11 or N14 CELECT Plus engines, so they can follow the factory pin checks, resistance measurements and step-by-step decisions instead of guessing at parts.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download it.
Applies to these truck models
This is the manufacturer document shared across 2 model families. It applies to:
- Cummins DTCs
- Cummins M11 CELECT Plus (1995-98)
Related manuals library
