Troubleshooting the M7504 Drive Communication Fault on a Bobcat S740

[MikePhua]

The Bobcat S740 and Its Electronic Control Architecture
The Bobcat S740 skid-steer loader is part of Bobcat’s high-performance lineup, designed for demanding applications in construction, agriculture, and industrial handling. With a rated operating capacity of 3,100 lbs and a turbocharged diesel engine producing around 74 horsepower, the S740 combines brute strength with refined control. Central to its operation is a network of electronic control modules (ECMs) that manage drive, lift, tilt, engine, and auxiliary functions through a CAN-bus communication system.
Terminology notes:

• CAN-bus: Controller Area Network, a protocol that allows multiple electronic modules to communicate efficiently.
  
• ECM: Electronic Control Module, a computer that governs specific machine functions such as drive or engine control.
  

The S740 typically houses up to seven controllers, including the mainframe controller, drive controller, joystick controller, and engine ECM. These modules must communicate seamlessly for the machine to operate correctly.
Understanding the M7504 Fault Code
The M7504 fault code indicates a “Drive No Communication” error. This means the mainframe controller cannot establish a signal with the drive controller, which is responsible for managing propulsion and directional control. When this fault occurs, the loader may lose drive function entirely, though lift and tilt may still operate.
Common symptoms:

• Machine powers on but won’t move
  
• Joysticks respond for lift/tilt but not for drive
  
• Warning lights or fault indicators on the display
  
• Horn or auxiliary functions may still work
  
• Switching joystick patterns (e.g., H-pattern) does not restore drive
  

In Tennessee, a contractor encountered this fault after pressure washing the machine. Moisture had seeped into the drive controller connector under the cab, triggering the fault.
Initial Diagnostic Steps
Before replacing components, a methodical inspection is essential:

• Check all fuses and relays related to the drive system
  
• Inspect the wiring harness behind the seat and under the cab
  
• Look for bent pins, corrosion, or loose connectors at the drive controller
  
• Verify power and ground at the controller using a multimeter
  
• Confirm continuity of CAN-bus lines between mainframe and drive controller
  
• Record the serial number to match the correct wiring diagram and controller variant
  

Recommended tools:

• Digital multimeter
  
• CAN-bus breakout box or diagnostic scanner
  
• Wiring schematic for the S740
  
• Contact cleaner and dielectric grease
  
• Flashlight and inspection mirror
  

Terminology notes:

• Continuity: A test to confirm that electrical current can flow through a wire or circuit.
  
• Bent pins: Misaligned or damaged connector terminals that disrupt signal transmission.
  

In Chile, a mining crew resolved the M7504 fault by reseating the drive controller connector and applying dielectric grease. The machine resumed normal operation without replacing any parts.
Controller Identification and Replacement Considerations
The S740 may use different drive controllers depending on production date and configuration. Common part numbers include #6679485 and others. Identifying the correct unit is critical before ordering replacements.
Steps:

• Locate the controller under the cab or seat
  
• Match part number and connector type
  
• Check for firmware compatibility if replacing with a used unit
  
• Ensure mounting bracket and harness length match original setup
  
• Perform post-installation calibration if required
  

In Ontario, a contractor replaced his drive controller with a salvaged unit from a T770. After updating the firmware and verifying CAN-bus integrity, the loader returned to full function.
Advanced Troubleshooting and CAN-bus Integrity
If basic checks don’t resolve the issue, deeper diagnostics may be needed:

• Use a CAN-bus analyzer to check for signal noise or dropped packets
  
• Inspect termination resistors at each end of the bus
  
• Test voltage levels on CAN-high and CAN-low lines
  
• Replace suspect wiring sections with shielded cable
  
• Check for ground loops or voltage spikes from other modules
  

Terminology notes:

• Termination resistor: A resistor placed at each end of a CAN-bus to prevent signal reflection.
  
• Ground loop: An unwanted electrical path that can cause interference or damage.
  

In South Africa, a vineyard crew traced intermittent M7504 faults to a damaged ground strap near the battery. Replacing the strap and rerouting the harness eliminated the issue permanently.
Preventive Measures and Long-Term Reliability
To avoid future communication faults:

• Avoid pressure washing near electronic connectors
  
• Inspect harnesses quarterly for abrasion or pinching
  
• Use sealed connectors and protective loom in high-vibration zones
  
• Keep diagnostic logs of fault codes and service actions
  
• Train operators to report faults immediately and avoid cycling power repeatedly
  

In Florida, a grading crew added a moisture barrier under the cab to protect the drive controller. The modification reduced electrical faults during rainy season operations.
Parts Availability and Sourcing Tips
Drive controllers and related components are available through:

• Authorized Bobcat dealers
  
• Aftermarket suppliers offering remanufactured modules
  
• Salvage yards with compatible S-series inventory
  
• Electronics shops for connectors and diagnostic tools
  

Sourcing advice:

• Match controller by serial number and software version
  
• Replace connectors with weatherproof types
  
• Seek wiring harness upgrades with improved shielding
  
• Use OEM-rated fuses and relays for reliability
  

In New Zealand, a contractor rebuilt his S740’s electrical system using marine-grade wire and sealed connectors. After 1,500 hours, the system remained fault-free.
Operator Stories and Field Wisdom
In Poland, a snow-clearing team used an S740 with a recurring M7504 fault. After installing a secondary ground and rerouting the harness, the machine ran through winter without issue.
In Alberta, a forestry crew added a diagnostic port extension to access the drive controller without lifting the cab. This reduced service time and improved fault resolution.
Conclusion
The M7504 fault code on a Bobcat S740 signals a breakdown in communication between the mainframe and drive controller. While the issue may seem daunting, most cases stem from wiring, connector, or grounding problems. With careful diagnostics, proper parts matching, and preventive care, the machine can be restored to full function without major overhaul. In the world of compact loaders, communication is everything—and keeping those signals clean and connected is the key to keeping the job moving.