This document is a CAT C15 122-05 manual covering diagnostic code 0122-05 (Med/High Retarder current low) for C15 On-Highway Truck engines with MXS configuration. It provides step-by-step solenoid circuit testing procedures, ECM connector pinouts, wiring schematics, and operating parameter checks required to isolate open and short circuit faults in the compression brake system. The guide is published under media number RENR5088-10.
Official CAT C15 122-05 document details
| Brand | Caterpillar (CAT) |
| Model coverage | C15 Truck Engine MXS (C15 On-Highway Truck MXS00001-UP) |
| System / Group | Engine Retarder (Compression Brake) Solenoid Circuit — SMCS 1129-038 |
| Publication no. | RENR5088-10 |
| Year / Revision | Published 01/02/2009, Updated 25/02/2009 |
| Pages | 17 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- 0122-05 Med/High Retarder Current Low (14) — Conditions, System Response
- Retarder (Compression Brake) Solenoid Circuit — Test: System Operation Description
- Customer Specified Parameters Affecting Retarder Operation
- Retarder Brake Test Procedure via Caterpillar Electronic Technician (Cat ET)
- Schematic for C15 Engines — P1 and P2 ECM Connector Pinouts
- Valve Cover Connectors for C15 Engines
- Test Step 1: Inspect Electrical Connectors and Wiring
- Test Step 3: Create a Short Circuit at the Valve Cover Connector
- Test Step 4: Create a Short Circuit at the ECM
- Test Step 6: Create an Open at the ECM
- Test Step 7: Create a Short Circuit at the Engine Retarder Solenoid
- Test Step 8: Create an Open Circuit at the Engine Retarder Solenoid
- Test Step 10: Check the Switch Circuit at the Firewall Bulkhead Connector
- Test Step 11: Check the Operating Parameters of the Engine Retarder
- Test Step 12: Check the Accelerator Pedal Position Sensor
- Test Step 13: Check the Clutch Switch
Applicable truck models
This manual applies to the Caterpillar C15 On-Highway Truck Engine, specifically the MXS serial number prefix (MXS00001-UP). It also references related DTCs 121-05, 121-06, 122-05, and 122-06 covering both Low/High and Med/High retarder solenoid circuits. The retarder solenoids are factory installed by Caterpillar and interface with OEM-installed switches. Vehicles equipped with SAE J1939 Anti-Lock Brake Systems or Eaton Top 2 transmissions may have additional relay configurations affecting retarder operation. For official Caterpillar product support, visit Caterpillar Support.
Who needs this CAT C15 122-05 manual
Diesel mechanics and workshop owners diagnosing an illuminated check engine lamp caused by DTC 0122-05 on a C15 engine will find the complete solenoid circuit test sequence, ECM connector pin locations (P1-5, P1-23, P1-40, P2-1, P2-8, P2-14), and valve cover terminal identifications needed to locate open or short circuit faults. The procedure requires Caterpillar Electronic Technician (Cat ET) software for the Retarder Brake Test.
The full 17-page PDF is available in the DiagTechPro manuals library, free account required to download.
Related manuals library
Related library topics: CAT C15 retarder troubleshooting; RENR5088-10; SMCS 1129-038; CAT; CAT C15 retarder troubleshooting manual; 0122-05 Med High Retarder current low; compression brake solenoid circuit test; C15 On-Highway Truck Engine MXS; ECM connector pinout P2; retarder brake test Cat ET.
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