Caterpillar D6R Diagnostic Codes: Interpretation, Common Causes, and Troubleshooting Guide

[MikePhua]

Understanding D6R Fault Codes and the SERV CODE System
The Caterpillar D6R features a sophisticated monitoring system that uses diagnostic codes (e.g., CID/FMI) to identify issues. When conditions trigger a code, the warning light flashes and the “SERV CODE” indicator appears in the lower message window. Once the fault is resolved, the flash may disappear but the code remains logged in memory.
How Fault Codes Are Structured

• CID (Component ID) identifies the affected sensor or module.
  
• FMI (Failure Mode Identifier) clarifies the nature of the fault:
  • 02 = Erratic, Intermittent or Incorrect signal
    
  • 03 = Voltage Above Normal
    
  • 04 = Voltage Below Normal
    
  • 13 = Out of Calibration
    
• For example, code 036.091.02 refers to Throttle Position Sensor signal being erratic.
  

Example Fault Codes Recorded Under Load

• 036 091 02 – Throttle Position Sensor, signal erratic
  
• 113 298 02 – Service Brake Pedal Switch, signal erratic
  
• 036 164 11 – Injection Actuation Pressure Sensor, other failure mode
  Codes were triggered only during heavy load or uphill operation.
  

Intermittent Faults During Load or Incline
A user noted slow throttle response and stalling when shifting from forward to reverse at low idle—especially under load. The engine surges after several seconds unless idle is raised; warning light appears only under heavy push uphill.
Common Root Causes by Code Type

• 036.Throttle Sensor and 036.Injection Pressure Sensor: may be starved of oil or fuel under incline if oil pickup is near front of engine—leading to sensor readings erratic under load. Slight overfill (up to 10%) can improve pickup during slope operation—but must be balanced to avoid overfill issues.
  
• 113.Service Brake Switch: intermittent signal faults—wiring or switch cleaning may resolve
  
• Users often avoided escalating repairs by first replacing fuel filters, engine oil, and using OEM Cat filters and oil to eliminate variables.
  

Testing and Diagnostic Procedures
Prior to component replacement:

• Scroll through DTC set list to see which are active vs logged
  
• Confirm whether SERV CODE indicator lights on each code, indicating real-time activation
  
• Monitor operation in varying conditions (load, idle rate, temperature) to reproduce fault trigger
  

If active under load and idle, consider adding fluid to prevent air starvation.
Additional Relevant D6R Codes
Per mechanic reference reports, other possible codes include:

• 248.02 – Cat® data link communication fault
  
• 271.06 / 324.06 – Alarm or warning lamp issues
  
• 168.03 / 168.04 – System voltage low condition
  
• 299.13 – Transmission lever position sensor out of calibration
  
• 671, 672, 673 codes – various transmission output speed sensor faults
  Each code maps to specific components and failure modes requiring targeted troubleshooting.
  

Term Glossary

• CID: Component Identifier code used by ECM
  
• FMI: Failure mode indicating nature of fault
  
• DTC (Diagnostic Trouble Code): Composite notation CID .FMI
  
• SERV CODE: Indicator that a DTC is active
  
• Oil Starvation: Loss of pump pressure due to low or settling fluid under incline
  

Step‑by‑Step Troubleshooting Flow

1. Capture all current codes using Cat ET or display function
   
2. Determine which codes show SERV CODE indicator active
   
3. Examine related sensor wiring and test for resistance, shorts, or corrosion
   
4. Add fluids carefully: oil and fuel if face starvation issues under slope (adhering to manual tolerance)
   
5. Replace suspect sensors one-at-a-time, starting with throttle position sensor or injection pressure sensor
   
6. After any repair, clear inactive codes using Cat ET and retest under load to verify resolution
   

Summary Table of Example Codes and Actions

• 036 091 02 – Throttle position erratic → inspect throttle sensor or harness
  
• 113 298 02 – Brake pedal switch intermittent → check switch and wiring
  
• 036 164 11 – Injection actuation pressure faulty → consider pressure starvation or sensor calibration
  
• 248.02 – Data link issue → inspect harness/connectors between ECM & display
  
• 299.13 – Transmission lever sensor out of calibration → recalibrate via service tool
  
• 671/672/673 – Speed sensor codes → test and replace output/intermediate speed sensors or wiring
  

Final Thoughts
Codes appearing primarily under load or slope often point to fluid or sensor electro-mechanical inconsistencies during low supply conditions. Simple measures—correct fluid levels, wiring and switch inspections, OEM filter replacements—resolve many issues. For persistent sensor-related codes, follow the diagnostic sensor test procedures in the service manual. When in doubt, Caterpillar ET remains the key for code retrieval, clearing inactive codes, and final validation.
By methodically identifying active fault codes, understanding FMI context, and validating fluid/oil conditions, many D6R issues can be solved in-house before resorting to parts replacements or ECM service.