This one-page troubleshooting document provides CAT C-12 auxiliary output procedures for diagnosing diagnostic trouble code 0026-05 (Auxiliary Output #01 current low, flash code 69). It covers the conditions that generate this fault code on 3406E, C-10, and C-12 on-highway truck engines, the ECM system response, and the required test steps to resolve the issue.
Official CAT C-12 auxiliary output document details
| Brand | Caterpillar (CAT) |
| Model coverage | C-12 Truck Engine 9NS00001-UP; also applicable to 3406E and C-10 engines (8YS, 9NS, 5DS, or 1LW configurations) |
| System / Group | DTCs — SMCS 1901-038 (Auxiliary Output #01 current low) |
| Publication no. | RENR1328-08 |
| Year / Revision | Published 01/10/2008, updated 16/10/2008 |
| Pages | 1 |
| File size | 0.1 MB |
| Format | |
| Language | English |
Document table of contents
- Conditions Which Generate This Code — ECM detection of low current (open circuit) in auxiliary output 01
- System Response — Solenoid behavior, neutral detection, manual operation mode, and Eaton Top 2 mode disabling
- Test Step 1 — Eaton Top 2 Transmission Circuit Test procedure and expected results
Applicable truck models
This troubleshooting guide applies to Caterpillar on-highway truck engines in the 3406E, C-10, and C-12 families. Specific serial number prefixes covered are 8YS, 9NS, 5DS, and 1LW. The document references the C-12 Truck Engine configuration 9NS00001-UP. These engines are commonly found in Class 8 heavy-duty trucks from various OEMs. Workshops servicing vehicles equipped with the Eaton Top 2 transmission paired with these CAT powertrains will find this code reference essential. For additional Caterpillar service literature and parts information, visit the Caterpillar official support page.
Who needs this C-12 auxiliary output manual
Diesel mechanics and workshop owners diagnosing DTC 0026-05 on 3406E, C-10, or C-12 engines need this document. It is particularly relevant when the ECM disables Eaton Top 2 mode and the transmission defaults to manual operation with both solenoids OFF, as understanding the fault conditions and circuit test procedure is critical for efficient repair.
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