This 12-page document is a C15 ambient temperature DTCs troubleshooting guide for diagnostic code 0171-03 (Ambient Air Temperature voltage high) on Caterpillar C15 on-highway truck engines (MXS configuration). It details the conditions that trigger the code, the ECM system response, and a complete seven-step diagnostic procedure for isolating open and short circuit faults in engine temperature sensor circuits.
Official C15 ambient temperature DTCs document details
| Brand | Caterpillar (CAT) |
| Model coverage | C15 Truck Engine MXS (MXS00001-UP) |
| System / Group | DTCs — Engine Temperature Sensors (SMCS 1439-038-AI; 1928-038) |
| Publication no. | RENR5088-10 |
| Year / Revision | Published 01/02/2009, updated 25/02/2009 |
| Pages | 12 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- 0171-03 Ambient Air Temperature Voltage High — Conditions Which Generate This Code
- System Response (ECM default to 65 °C / 149 °F; Allow Idle Shutdown Override disabled)
- Engine Temperature Sensor Open or Short Circuit — Test (covers codes 105-03, 105-04, 110-03, 110-04, 171-03, 171-04, 174-03, 174-04)
- Pull-up Voltage explanation and schematics (Illustrations 1–5)
- P1 and P2 ECM connector pin assignments and sensor locations
- Test Step 1 — Inspect Electrical Connectors and Wiring (45 N pull test, torque check)
- Test Step 2 — Check for Active Diagnostic Codes via Cat ET
- Test Step 3 — Disconnect Suspect Sensor to Create Open Circuit
- Test Step 4 — Check Pull-up Voltage at Sensor Connector (5.5 ± 0.5 VDC)
- Test Step 5 — Check Signal Wire for Short Circuit (resistance > 20,000 Ohms)
- Test Step 6 — Create a Short at the Suspect Sensor Connector (jumper wire test)
- Test Step 7 — Check the Operation of the ECM (open/short simulation at ECM pins)
Applicable truck models
This procedure applies to the Caterpillar C15 on-highway truck engine, configuration MXS00001-UP. It addresses the ambient air temperature sensor circuit routed through ECM connector P1 (pin P1-26 for signal, P1-18 for sensor common). The same underlying test procedure also covers the intake manifold air temperature sensor, coolant temperature sensor, and fuel temperature sensor wired through ECM connector P2. Engines running software dated after December 2003 use a revised 4.95 VDC threshold instead of 4.92 VDC. For official parts and service information, visit Caterpillar Support.
Who needs this C15 ambient temperature DTCs manual
Fleet mechanics and independent workshop technicians diagnosing a 0171-03 active fault code on a C15 MXS engine will find this guide essential. It is equally useful for anyone troubleshooting related temperature sensor codes (105, 110, 174) since all four sensors share identical diagnostic steps.
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