This 11-page PDF is an official CAT C15 key switch fault troubleshooting document for the C15 On-Highway Truck Engine (MXS series). It provides step-by-step diagnostic procedures for DTC 0043-02, which is triggered when the Engine Control Module (ECM) detects three or more keyswitch cycles within one second, indicating an intermittent or low battery condition. The guide walks technicians through connector inspection, voltage measurement, battery load testing, and vehicle harness bypass procedures.
Official CAT C15 key switch fault document details
| Brand | Caterpillar (CAT) |
| Model coverage | C15 Truck Engine MXS (MXS00001-UP) |
| System / Group | Ignition Keyswitch Circuit and Battery Supply Circuit — DTCs |
| Publication no. | RENR5088-10 |
| Year / Revision | Published 01/02/2009, Updated 25/02/2009 |
| Pages | 11 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- 0043-02 Key Switch Fault (71) — Conditions Which Generate This Code, System Response
- Ignition Keyswitch Circuit and Battery Supply Circuit — Test (System Operation Description)
- Test Step 1: Inspect the Electrical Connectors and the Wiring
- Test Step 2: Use Cat ET to Check for Communications with the ECM
- Test Step 3: Check for Active Diagnostic Codes or Logged Diagnostic Codes
- Test Step 4: Check for Battery Voltage at the ECM Connector
- Test Step 5: Check the Batteries
- Test Step 6: Bypass the Vehicle Harness
Applicable truck models
This document applies to the Caterpillar C15 On-Highway Truck Engine, configuration MXS00001-UP. It covers 12-volt and 24-volt electrical systems and addresses DTC 0043-02 along with related codes 168-2 (ECM Battery Power Intermittent), 168-3 (High ECU Battery Power), and 168-4 (Low ECU Battery Power). The procedure references ECM connector terminals at the J1/P1 connector, including P1-48, P1-52, P1-53 for unswitched +Battery and P1-63, P1-65, P1-67 for −Battery, plus P1-70 for keyswitch input. It also covers use of the 167-9225 Harness (Service Tool Adapter) and 4C-4911 Battery Load Tester. For additional Caterpillar product and support resources, visit the official Caterpillar website.
Who needs this CAT C15 key switch fault manual
Diesel mechanics and workshop owners troubleshooting intermittent engine shutdowns, no-start conditions, or check engine lamp illumination on C15-powered trucks will find this guide essential. It is also relevant for technicians diagnosing aftermarket engine protection shutdown systems or idle timer shutdown systems that interrupt ECM power.
The full PDF is available in the DiagTechPro manuals library, free account required to download.
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