This document is a CAT 0232-03 5 Volt Supply troubleshooting guide that addresses diagnostic code 21 for Caterpillar on-highway truck engines. It details the conditions that generate the code, the ECM system response including default sensor values, and the recommended test procedure. The guide is essential for diagnosing overvoltage faults on the 5 volt sensor supply circuit.
Official CAT 0232-03 5 Volt Supply document details
| Brand | Caterpillar (CAT) |
| Model coverage | 3406E, C-10, C-12 Truck Engines (configurations 8YS, 9NS, 5DS, 1LW) |
| System / Group | Engine Control Module (ECM) — 5 Volt Supply Voltage Diagnostics (SMCS 5574-038) |
| 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
- 0232-03 5 Volt Supply voltage high (21) — Conditions Which Generate This Code
- System Response — ECM default sensor values for coolant temperature, fuel temperature, intake manifold air temperature, engine oil pressure, atmospheric pressure, boost pressure, coolant level, and outside air temperature
- Test Step 1 — 5 Volt Engine Pressure Sensor Supply Circuit Test
Applicable truck models
This troubleshooting document 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 configuration example listed is the C-12 Truck Engine 9NS00001-UP. These engines are widely used in Class 8 heavy-duty trucks across multiple OEM chassis. For official Caterpillar parts lookup, technical bulletins, and service tools, visit Caterpillar Support and Service Resources.
Who needs this 0232-03 5 Volt Supply manual
Fleet mechanics and independent workshop technicians diagnosing low-power complaints or active “DIAG” lamp codes on 3406E, C-10, or C-12 engines need this reference. It provides the exact voltage threshold (5.16 VDC for more than one second), every default sensor value the ECM substitutes during the fault, and the single required test step to isolate the 5 volt pressure sensor supply circuit.
The full PDF is available in the DiagTechPro manuals library, free account required to download.
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