Cummins fault code 1866 is the Cummins Exhaust Gas Recirculation Valve Delta Pressure – Data Erratic, Intermittent, or Incorrect document for the ISX11.9 CM2250 (2010-12) engine platform, a 14-page PDF that reproduces the official fault code write-up read with Cummins INSITE. The EGR differential (delta) pressure sensor reads the pressure drop across an orifice in the EGR tube so the ECM can calculate EGR flow into the intake manifold, and it runs an autozero test at key OFF.
Official document details
| Brand | Cummins |
| Model coverage | Cummins ISX11.9, ISX15, ISB6.7, ISC8.3 and ISL9 CM2250 |
| System / group | ISX11.9 CM2250 (2010-12) / DTCs |
| Fault code | 1866 — PID P411, SPN 411, FMI 2 |
| Warning lamp | Amber |
| Publication reference | Cummins troubleshooting bulletin 2883445 (differential pressure sensor circuit) |
| Pages | 14 |
| File size | 0.2 MB |
| Format | |
| Language | English |
What Cummins fault code 1866 means
It sets when the EGR delta pressure reads higher or lower than a calibratable value at key OFF, or the sensor fails the autozero test. EGR valve actuation is disabled, diesel exhaust fluid injection and both regenerations are disabled, and the EGR valve closes. The document walks a technician through the summary and the guided troubleshooting steps needed to confirm and clear the code.
Document table of contents
- Overview and circuit description
- Component location
- Conditions for running the diagnostics
- Conditions for setting the fault code
- Action taken when the fault code is active
- Conditions for clearing the fault code
- Shop Talk and possible causes
- Associated procedures and guided troubleshooting steps
Applicable truck models
This troubleshooting document covers Cummins ISX11.9, ISX15, ISB6.7, ISC8.3 and ISL9 CM2250 engines in Class 6 to 8 trucks. It is filed under the ISX11.9 CM2250 (2010-12) / DTCs group and also applies to ISX12 CM2250 installations, so confirm the engine dataplate before ordering parts. Cross-reference the calibration revision with Cummins official engine support before clearing the code.
Who needs this Cummins fault code 1866 manual
Heavy-duty diesel technicians, fleet maintenance teams and workshop owners diagnosing an erratic EGR delta pressure signal use this reference to read SPN 411 / FMI 2 correctly and to follow the guided steps in INSITE. The possible causes it lists include:
- an EGR delta pressure signal error at key ON
- a failed autozero test
- a plugged port or failed delta pressure sensor
The full 14-page PDF for EGR delta pressure fault code 1866 is available in the DiagTechPro manuals library; a free account is required to download.
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