No Throttle Response on John Deere 670J Dozer: Diagnosis, Causes, and Real-World Solutions

[MikePhua]

This article offers a comprehensive, reader‑friendly overview of no-throttle-response issues on John Deere 670J dozers. It spans diagnostic steps, technical definitions, real-life cases, and preventative guidance to empower technicians and operators.
Understanding the Throttle Response Failure
When a 670J dozer shows no throttle response—even though the engine idles but will not increase RPMs—or shows codes like F9C3, F423, and F9C4, this typically indicates communication failures among control modules via the CAN bus (Controller Area Network). Key modules include:

• ECU (Engine Control Unit)
  
• TCU (Transmission Control Unit)
  
• MDU (Machine Display Unit)
  

Error codes such as F9C3 and F9C4 point to the display unit not receiving messages from TCU and ECU, while F423 means the ECU is not receiving throttle data from the TCU .
Main Causes Identified

1. CAN Bus Faults: Damaged wiring harnesses, corroded plugs, or failed termination resistors can disrupt communication between control modules .
   
2. Faulty Module Connections: Corrosion at the ECM housing connector can impair communication, causing false codes and control failures .
   
3. Defective ECU or TCU: Physical damage or contamination in modules or their circuit boards can prevent proper command relay.
   

Step‑by‑Step Troubleshooting Checklist

• Read and Interpret Error Codes: Confirm F9C3, F9C4, F423 reflect module communication issues.
  
• Inspect Fuses and Relays: Ensure modules have consistent power supply. Replace any relay or fuse that shows partial voltage drop .
  
• Test CAN Bus Resistance: Use a multimeter to measure resistance between green and yellow wires at the 9‑pin connector by the TCU. Expected resistance is around 60 Ω with the machine off .
  
• Examine Harness and Connections: Pay special attention to misrouting, wire chafing, and connectors under the cab floor or near module mounts, which may pinch wiring during vibration or cab movement .
  
• Inspect ECU and TCU for Corrosion: Open module cases (carefully, per safety procedures) to check for moisture or rust near PCB contacts and connectors .
  

Technical Glossary

• CAN Bus: A robust vehicle network standard for digital communication between control units.
  
• Termination Resistors: 120 Ω resistors placed at each end of a CAN network to ensure signal integrity.
  
• Module Communication: The exchange of digital signals among ECU, TCU, and display units.
  
• Diagnostic Codes: Error indicators logged by onboard systems identifying module or circuit failure.
  

Real‑World Examples

• One operator found that after clearing codes the dozer would briefly respond before cutting out again—indicating intermittent module communication, characteristic of bad CAN linkage or failing modules .
  
• Technicians replaced termination resistors and repaired chafed harnesses under the cab, which restored throttle control in similar models.
  
• In one unit, corrosion had compromised the ECU board beneath the powder-coated housing, resulting in multiple erratic fault codes and complete loss of throttle—remedying the issue required module repair or replacement .
  

Preventive Maintenance Suggestions

• Routinely inspect wiring harnesses, especially near cab mounts and underfloor areas prone to pinching and wear.
  
• Make sure module connectors are clean and free from corrosion. Apply dielectric grease where appropriate.
  
• Test CAN bus resistance and function periodically, especially after adding electrical accessories.
  
• Repair or replace damaged termination resistors, often found near ECU and TCU locations.
  
• Update module software or recalibrate after any module replacement or battery disconnection.
  

Summary Checklist

• Confirm presence and meaning of fault codes (F9C3, F423, F9C4)
  
• Test fuse and relay power circuits feeding modules
  
• Measure CAN bus resistance at key connectors (~60 Ω)
  
• Examine harness routing and condition around junctions
  
• Inspect ECU/TCU modules for corrosion or water ingress
  
• Repair or replace faulty wiring, connectors, or termination resistors
  
• Re-test system after repair to verify restored throttle function
  

Conclusion
No throttle response on the JD 670J dozer is commonly linked to CAN bus communication failures rather than mechanical throttle linkage issues. By following structured diagnostics—interpreting error codes, testing circuits, and inspecting electrical modules—technicians can isolate and resolve the root cause efficiently. Consistent harness upkeep and early detection of wiring or module faults help prevent prolonged machine downtime and ensure reliable throttle control and safe machine operation.