10-15-2025, 12:00 PM
The John Deere 700K and Its Electronic Evolution
The John Deere 700K crawler dozer represents a significant leap in mid-size earthmoving equipment, combining hydrostatic drive with advanced electronic control systems. Introduced in the early 2010s, the 700K was part of Deere’s K-Series lineup, which emphasized operator comfort, fuel efficiency, and digital diagnostics. The machine features an Intelligent Grade Control (IGC) system, electrohydraulic (EH) valves, and multiple Controller Area Network (CAN) buses to manage communication between the engine, transmission, display, and external systems like GPS. With thousands of units sold globally, the 700K remains a staple in construction fleets, particularly in grading and site prep applications.
Understanding CAN Bus and Terminating Resistance
The CAN bus is a robust, differential two-wire communication protocol used in heavy equipment to allow multiple electronic control units (ECUs) to exchange data. Each CAN network must be properly terminated with two 120-ohm resistors—one at each end of the bus—to prevent signal reflection and ensure data integrity. When both resistors are present and functional, the total resistance across the CAN lines should read approximately 60 ohms. Deviations from this value often indicate a missing or failed resistor, shorted wiring, or a faulty controller.
Symptoms of CAN Instability on the 700K
In one case involving a 700K dozer, technicians observed erratic resistance readings on the IGC CAN network. With the machine powered off and the display disconnected, resistance between the CAN high and low lines initially measured 1.7 ohms—far below the expected 60 ohms. Interestingly, cycling the ignition key briefly caused the resistance to spike to 120 ohms before dropping back to 1.7 ohms. This behavior suggested that one of the terminating resistors was electronically controlled or embedded within a module that only activates under certain conditions.
Is John Deere Using Electronic Terminating Resistors?
While some agricultural equipment manufacturers have experimented with electronically switched resistors, these are rare in construction machinery due to reliability concerns. In this case, the suspicion was that the EH controller might house the second resistor, especially since the display was confirmed to be on a separate CAN network. The IGC network, which includes the EH controller and GPS interface, showed unstable voltage levels—both CAN high and low lines were stuck at 1.7 volts, indicating a bus fault.
Diagnostic Strategy and Pin-Level Testing
Technicians attempted to isolate the issue by measuring resistance at various diagnostic connector pins. On the 700K, pins C and D typically correspond to one CAN network, while pins J and H serve another. By inserting a known-good 120-ohm resistor across J and H, the technician was able to temporarily stabilize communication, suggesting that the original terminating resistor on that segment had failed or was missing.
Further testing involved measuring resistance between pins 10 and 11 on the EH controller, which are believed to be the CAN high and low lines. With the EH controller unplugged, resistance remained abnormal, reinforcing the theory that the controller itself housed the second resistor and had failed internally.
The Role of GPS and Network Load
The machine in question was equipped with a GPS grade control system. Although the GPS system was initially blamed for the CAN instability, disconnecting it had no effect on the resistance readings. This ruled out external interference and pointed squarely at the internal CAN architecture. It’s worth noting that CAN networks can operate with degraded resistance under light traffic, but as data load increases—such as during full GPS operation—signal integrity becomes critical. In this case, the network likely collapsed under load due to improper termination.
Error Codes and Historical Clues
The machine’s diagnostic memory revealed several inactive fault codes, including SDM 3156.9 (loss of communication with the EH controller). Although these codes were not active at the time of testing, they provided historical evidence of intermittent communication failures. This aligns with the theory that the EH controller’s internal resistor was failing intermittently, especially under thermal or electrical stress.
Recommendations and Long-Term Fixes
To resolve such issues, technicians should:
Conclusion
The John Deere 700K’s CAN resistance anomaly illustrates the complexity of modern heavy equipment diagnostics. While the machine’s hydrostatic drivetrain and grade control systems offer impressive performance, they also demand a new level of electrical literacy from technicians. Understanding the behavior of CAN networks, especially the role of terminating resistors, is essential for maintaining uptime in today’s connected job sites.
The John Deere 700K crawler dozer represents a significant leap in mid-size earthmoving equipment, combining hydrostatic drive with advanced electronic control systems. Introduced in the early 2010s, the 700K was part of Deere’s K-Series lineup, which emphasized operator comfort, fuel efficiency, and digital diagnostics. The machine features an Intelligent Grade Control (IGC) system, electrohydraulic (EH) valves, and multiple Controller Area Network (CAN) buses to manage communication between the engine, transmission, display, and external systems like GPS. With thousands of units sold globally, the 700K remains a staple in construction fleets, particularly in grading and site prep applications.
Understanding CAN Bus and Terminating Resistance
The CAN bus is a robust, differential two-wire communication protocol used in heavy equipment to allow multiple electronic control units (ECUs) to exchange data. Each CAN network must be properly terminated with two 120-ohm resistors—one at each end of the bus—to prevent signal reflection and ensure data integrity. When both resistors are present and functional, the total resistance across the CAN lines should read approximately 60 ohms. Deviations from this value often indicate a missing or failed resistor, shorted wiring, or a faulty controller.
Symptoms of CAN Instability on the 700K
In one case involving a 700K dozer, technicians observed erratic resistance readings on the IGC CAN network. With the machine powered off and the display disconnected, resistance between the CAN high and low lines initially measured 1.7 ohms—far below the expected 60 ohms. Interestingly, cycling the ignition key briefly caused the resistance to spike to 120 ohms before dropping back to 1.7 ohms. This behavior suggested that one of the terminating resistors was electronically controlled or embedded within a module that only activates under certain conditions.
Is John Deere Using Electronic Terminating Resistors?
While some agricultural equipment manufacturers have experimented with electronically switched resistors, these are rare in construction machinery due to reliability concerns. In this case, the suspicion was that the EH controller might house the second resistor, especially since the display was confirmed to be on a separate CAN network. The IGC network, which includes the EH controller and GPS interface, showed unstable voltage levels—both CAN high and low lines were stuck at 1.7 volts, indicating a bus fault.
Diagnostic Strategy and Pin-Level Testing
Technicians attempted to isolate the issue by measuring resistance at various diagnostic connector pins. On the 700K, pins C and D typically correspond to one CAN network, while pins J and H serve another. By inserting a known-good 120-ohm resistor across J and H, the technician was able to temporarily stabilize communication, suggesting that the original terminating resistor on that segment had failed or was missing.
Further testing involved measuring resistance between pins 10 and 11 on the EH controller, which are believed to be the CAN high and low lines. With the EH controller unplugged, resistance remained abnormal, reinforcing the theory that the controller itself housed the second resistor and had failed internally.
The Role of GPS and Network Load
The machine in question was equipped with a GPS grade control system. Although the GPS system was initially blamed for the CAN instability, disconnecting it had no effect on the resistance readings. This ruled out external interference and pointed squarely at the internal CAN architecture. It’s worth noting that CAN networks can operate with degraded resistance under light traffic, but as data load increases—such as during full GPS operation—signal integrity becomes critical. In this case, the network likely collapsed under load due to improper termination.
Error Codes and Historical Clues
The machine’s diagnostic memory revealed several inactive fault codes, including SDM 3156.9 (loss of communication with the EH controller). Although these codes were not active at the time of testing, they provided historical evidence of intermittent communication failures. This aligns with the theory that the EH controller’s internal resistor was failing intermittently, especially under thermal or electrical stress.
Recommendations and Long-Term Fixes
To resolve such issues, technicians should:
- Verify resistance across all CAN networks with power off and all modules connected
- Identify which modules contain internal resistors using service documentation
- Temporarily insert external resistors to confirm diagnosis
- Replace suspect controllers if internal resistors are confirmed faulty
- Use an oscilloscope to verify signal integrity under load
Conclusion
The John Deere 700K’s CAN resistance anomaly illustrates the complexity of modern heavy equipment diagnostics. While the machine’s hydrostatic drivetrain and grade control systems offer impressive performance, they also demand a new level of electrical literacy from technicians. Understanding the behavior of CAN networks, especially the role of terminating resistors, is essential for maintaining uptime in today’s connected job sites.
