Yesterday, 03:17 PM
The operator encountered an active error reading 1701-5, signaling an open-circuit condition in the fan-drive solenoid. This indicates the electronic actuator that powers the cooling fan is not receiving or completing the electrical path. Additionally, the feature that allows the fan to reverse its rotation is not responding.
Location of Control Unit
The machine’s Transmission Control Unit (TCU), which issues the command to the fan-drive solenoid, is positioned behind the operator’s display in the cab. Two wires extend from the TCU to the fan solenoid: one colored green (identified as H02), and one black (G11). The green wire carries the control signal from pin 14 of the bottom (X2) connector on the TCU. The black wire provides the electrical return path (ground) through the starter assembly. If this ground connection is loose or corroded, both the fan drive and its reverse function may fail.
Small Anecdote
Picture a foreman on a chilly morning discovering his machine’s fan won’t reverse. He fiddles with controls, gets no response, but then a local tech reminds him: “Have you checked the ground at the starter?” A quick tighten solves it, the fan spins in reverse at the push of a button, and the day moves along smoothly—highlighting how a simple ground fix can avert a major headache.
Equipment Background
The JD 750J is a crawler-type bulldozer from John Deere’s medium-duty line, featuring a robust hydrostatic transmission and a sophisticated hydraulic fan system. Developed in the early 2000s, it builds on decades of John Deere’s earthmoving machinery expertise. Although exact global sales numbers are not publicly published, this model has been widely adopted across construction, forestry, and mining due to its balance of power (typically powered by a 6.8 L PowerTech engine), reliability, and operator comfort.
John Deere—the company behind it—originated in the 19th century as a plow maker and through steady innovation grew into a leader in agricultural and construction equipment. The 750J reflects that heritage: rugged engineering paired with advanced electronics and hydraulics.
Glossary of Key Terms
• Ground Verification: Check the starter ground point where the black G11 wire is grounded. Ensure clean, tight, corrosion-free contact.
• Wire Integrity: Visually inspect H02 (green) and G11 (black) wiring for abrasion, breaks, or loose connectors—especially at the TCU connector X2.
• Connector Cleaning: Use approved electrical contact cleaner, then apply dielectric grease to prevent future corrosion.
• Functional Test: With a multimeter, monitor for proper voltage at H02 during engine operation or fan-reverse commands. Confirm continuity on G11 to chassis or starter.
• Diagnostic Scan: Use John Deere’s Service ADVISOR or similar diagnostic tool to monitor the TCU’s state and see if commands are reaching the solenoid.
• Complete Troubleshooting Flow:
According to maintenance documentation for the 750J (circa April 2022), hydraulic system oil and filters—including those serving the fan return—and hydrostatic transmission oil should be serviced roughly every 2,000 hours. These intervals ensure optimal hydraulic flow and cooling system performance and can influence behavior of components including the fan drive system.
Final Takeaway
A fault like 1701-5 in the JD 750J often stems from an interrupted electrical circuit—typically involving a missing ground or wiring issue—rather than a full component failure. Because the fan reverse function shares that ground path, both systems going dark suggest a shared root cause. A focused check of the ground at the starter, along with signal verification from the TCU, usually resolves the issue. Regular maintenance and attention to electrical connections can prevent recurrence.
Location of Control Unit
The machine’s Transmission Control Unit (TCU), which issues the command to the fan-drive solenoid, is positioned behind the operator’s display in the cab. Two wires extend from the TCU to the fan solenoid: one colored green (identified as H02), and one black (G11). The green wire carries the control signal from pin 14 of the bottom (X2) connector on the TCU. The black wire provides the electrical return path (ground) through the starter assembly. If this ground connection is loose or corroded, both the fan drive and its reverse function may fail.
Small Anecdote
Picture a foreman on a chilly morning discovering his machine’s fan won’t reverse. He fiddles with controls, gets no response, but then a local tech reminds him: “Have you checked the ground at the starter?” A quick tighten solves it, the fan spins in reverse at the push of a button, and the day moves along smoothly—highlighting how a simple ground fix can avert a major headache.
Equipment Background
The JD 750J is a crawler-type bulldozer from John Deere’s medium-duty line, featuring a robust hydrostatic transmission and a sophisticated hydraulic fan system. Developed in the early 2000s, it builds on decades of John Deere’s earthmoving machinery expertise. Although exact global sales numbers are not publicly published, this model has been widely adopted across construction, forestry, and mining due to its balance of power (typically powered by a 6.8 L PowerTech engine), reliability, and operator comfort.
John Deere—the company behind it—originated in the 19th century as a plow maker and through steady innovation grew into a leader in agricultural and construction equipment. The 750J reflects that heritage: rugged engineering paired with advanced electronics and hydraulics.
Glossary of Key Terms
- TCU (Transmission Control Unit): The electronic module that governs gear changes and controls auxiliary hydraulic functions, including the fan drive.
- Proportional Solenoid: An electrically actuated valve that modulates flow based on input current, used here to control fan speed.
- Ground (Electrical): The return path for current; must be secure to complete the circuit.
- Fan Reverse Function: A feature that enables the cooling fan to switch rotation direction, helping clear debris from the radiator.
- Engine: John Deere PowerTech 6.8 L diesel
- Hydraulic system capacity: ~106 L (28 gal)
- Hydraulic oil filter change interval: ~2,000 operating hours
- Hydrostatic transmission oil: similar capacity
- Diagnostic code 1701-5: open circuit to fan drive solenoid
• Ground Verification: Check the starter ground point where the black G11 wire is grounded. Ensure clean, tight, corrosion-free contact.
• Wire Integrity: Visually inspect H02 (green) and G11 (black) wiring for abrasion, breaks, or loose connectors—especially at the TCU connector X2.
• Connector Cleaning: Use approved electrical contact cleaner, then apply dielectric grease to prevent future corrosion.
• Functional Test: With a multimeter, monitor for proper voltage at H02 during engine operation or fan-reverse commands. Confirm continuity on G11 to chassis or starter.
• Diagnostic Scan: Use John Deere’s Service ADVISOR or similar diagnostic tool to monitor the TCU’s state and see if commands are reaching the solenoid.
• Complete Troubleshooting Flow:
- Inspect ground – tighten or repair as needed
- Inspect wiring from TCU to solenoid – repair any damage
- Confirm signal pulses from TCU during fan reverse operation
- If wiring and signal are good, check the solenoid’s internal coil resistance and operation
- As last resort, replace the fan drive solenoid if it fails electrical or functional tests
According to maintenance documentation for the 750J (circa April 2022), hydraulic system oil and filters—including those serving the fan return—and hydrostatic transmission oil should be serviced roughly every 2,000 hours. These intervals ensure optimal hydraulic flow and cooling system performance and can influence behavior of components including the fan drive system.
Final Takeaway
A fault like 1701-5 in the JD 750J often stems from an interrupted electrical circuit—typically involving a missing ground or wiring issue—rather than a full component failure. Because the fan reverse function shares that ground path, both systems going dark suggest a shared root cause. A focused check of the ground at the starter, along with signal verification from the TCU, usually resolves the issue. Regular maintenance and attention to electrical connections can prevent recurrence.
