This document is a CAT 0171-04 ambient air temperature troubleshooting guide covering diagnostic code 0171-04 (voltage low) for Caterpillar 3406E, C-10, and C-12 on-highway truck engines. It details the conditions that generate the fault code, the ECM system response and default behavior, and the recommended diagnostic test procedure to resolve the issue.
Official CAT 0171-04 ambient air temperature document details
| Brand | Caterpillar (CAT) |
| Model coverage | 3406E, C-10, C-12 Truck Engines (8YS, 9NS, 5DS, 1LW prefixes) |
| System / Group | Diagnostic Trouble Codes (DTCs) — SMCS 1928-038 |
| 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
- System Response
- Test Step 1: Engine Temperature Sensor Open or Short Circuit – Test
Applicable truck models
This troubleshooting procedure applies to Caterpillar on-highway truck engines in the 3406E, C-10, and C-12 families. The specific configuration referenced is the C-12 Truck Engine 9NS00001-UP, but the document also covers serial prefixes 8YS, 5DS, and 1LW. The fault code 0171-04 is triggered when the Engine Control Module (ECM) detects that the ambient air temperature sensor signal voltage drops below 0.2 VDC for more than eight seconds and the “Allow Idle Shutdown Override” parameter is programmed to “Outside Temperature Based” or “J1587 Outside Temperature Based.” When active, the ECM defaults the outside air temperature reading to 65 °C (149 °F) and disables the idle shutdown override function. The diagnostic status “DIAG” appears next to “Outside Temperature Sensor” in the Caterpillar Electronic Technician (ET) software. The recommended repair path directs the technician to perform the Engine Temperature Sensor Open or Short Circuit test procedure. For additional Caterpillar technical resources, visit the Caterpillar official support page.
Who needs this CAT 0171-04 ambient air temperature manual
Fleet mechanics, independent diesel technicians, and workshop owners servicing Caterpillar 3406E, C-10, or C-12 powered trucks will find this guide essential when diagnosing a 0171-04 voltage low fault code on the ambient air temperature sensor circuit. It provides the exact ECM trigger conditions, default values, and the correct diagnostic test to follow.
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