This document is a CAT C-12 coolant warning troubleshooting guide that covers diagnostic code 0111-01 (Low Coolant Level Warning, FMI 62) for Caterpillar 3406E, C-10, and C-12 on-highway truck engines. It provides the conditions that generate the code, the ECM system response, and a step-by-step diagnostic procedure to identify and resolve the root cause of a low coolant level alert.
Official CAT C-12 coolant warning document details
| Brand | Caterpillar (CAT) |
| Model coverage | C-12 Truck Engine 9NS (9NS00001-UP); also applicable to 3406E, C-10 |
| System / Group | Troubleshooting — DTCs / SMCS 5574-038-CLT (Coolant Level) |
| Publication no. | RENR1328-08 |
| Year / Revision | Published 01/10/2008, updated 16/10/2008 |
| Pages | 2 |
| File size | 0.1 MB |
| Format | |
| Language | English |
Document table of contents
- 0111-01 Low Coolant Level Warning (62) — Conditions Which Generate This Code
- System Response (ECM behavior, check engine lamp, warning lamp, low coolant level lamp)
- Test Step 1 — Check the Coolant Level
- Test Step 2 — Check for Leaks in the Cooling System
Applicable truck models
This troubleshooting procedure applies to Caterpillar truck engines in the 3406E, C-10, and C-12 families, specifically the C-12 configuration 9NS00001-UP. These engines are commonly found in Class 8 on-highway trucks from multiple OEMs. The diagnostic code 0111-01 is triggered when the ECM detects that the coolant level has remained low for more than ten seconds. The system response includes illumination of the check engine lamp and the warning lamp (or a dedicated low coolant level lamp if installed). Factory passwords are required to clear this code after the underlying problem is resolved. The guide directs technicians first to verify the coolant level and sensor installation, then to inspect for external leaks and coolant contamination in the engine oil. For additional service information, visit the Caterpillar official support page.
Who needs this CAT C-12 coolant warning manual
Diesel mechanics and workshop owners troubleshooting a persistent low coolant level warning on 3406E, C-10, or C-12 powered trucks will find this guide essential. It is also useful for fleet maintenance teams who need to verify coolant sensor installation or diagnose cooling system leaks before clearing the diagnostic code with factory passwords.
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