7 hours ago
Unpredictable Speed Control Stutter
Operators of the 750C Series II often experience sudden loss or fluctuation in speed—machines dropping to low speed “1,” jumping to “3,” or completely refusing to move—while fault codes flash simultaneously. One case reported error codes F654 and F658, which correspond to issues like:
Voltage Checks and Signal Diagnostics
A reliable method is to back-probe the joystick switch’s signal wire and confirm two key voltages:
Common Fault Codes and Sensor مشکلات
Other frequent fault codes on this model and related Deere machines include:
Moisture and Connector Corrosion – A Hidden Culprit
Several owners found speed sensor failures following pressure washing or wet-season operations. A tiny amount of moisture in the sensor or corroded connector can derail readings instantly. Inspecting and cleaning connectors behind the shift lever or relevant control box often resolves sudden faults. This phenomenon is particularly noted in 850C models but applies to 750C as well.
Transmission Controller Diagnostics (Fault Code Patterns)
According to Deere’s diagnostic documentation:
Quick Reference Overview
An operator faced intermittent speed loss and F654/F658 codes that reoccurred after cleaning the joystick switch. Back-probing showed correct output voltage at the switch, but readings dropped at the TCU connector. Tracing the harness revealed a pin misaligned in a sealed multiplug. Reseating the pin restored voltage continuity; the dozer ran smoothly all week afterward with no further codes.
In summary, the 750C II’s speed-control issues often trace back to electrical signal integrity—either through bad voltage, misaligned sensors, or wet/corroded connectors. Systematic voltage checks, harness tracing, and protecting connections against moisture dramatically improve reliability and reduce needless parts replacement.
Operators of the 750C Series II often experience sudden loss or fluctuation in speed—machines dropping to low speed “1,” jumping to “3,” or completely refusing to move—while fault codes flash simultaneously. One case reported error codes F654 and F658, which correspond to issues like:
- F654: Transmission Speed Control Switch voltage falling below 0.5 V
- F658: Decelerator/Speed Control Sensor signal shorted to ground
Voltage Checks and Signal Diagnostics
A reliable method is to back-probe the joystick switch’s signal wire and confirm two key voltages:
- A stable 5 V reference supply to the switch
- A signal output above 0.5 V when the switch is operated
Common Fault Codes and Sensor مشکلات
Other frequent fault codes on this model and related Deere machines include:
- F627 / F635: Speed sensor/pickup alignment or wiring issues, typically causing steering faults or speed inconsistencies
- F640: Hydrostatic Pump Speed sensor malfunction—often speed drops or “return to neutral” messages appear; cleaning, repositioning, or replacing sensor resolves it
Moisture and Connector Corrosion – A Hidden Culprit
Several owners found speed sensor failures following pressure washing or wet-season operations. A tiny amount of moisture in the sensor or corroded connector can derail readings instantly. Inspecting and cleaning connectors behind the shift lever or relevant control box often resolves sudden faults. This phenomenon is particularly noted in 850C models but applies to 750C as well.
Transmission Controller Diagnostics (Fault Code Patterns)
According to Deere’s diagnostic documentation:
- F3 + 6x codes relate to transmission speed sensor or hydrostatic pump speed feedback issues
- Codes ending in 0, 2, or 5 signal open or short circuits—meaning voltage signal loss
Quick Reference Overview
- F654: Transmission Speed Control voltage < 0.5 V
- F658: Switch circuit short to ground
- F627/F635: Misaligned or wrong speed sensor or wiring
- F640: Hydrostatic pump speed sensor failure
- Sensor issues often show up after water exposure
- Deere codes (F3x) provide insight into specific circuit failures
- Use a multimeter/back-probe testing to trace voltage from switch through harness to TCU
- Visually inspect connectors for moisture, corrosion, or misalignment—especially after pressure washing
- Ensure sensors are correctly positioned relative to reluctor discs—too close or too far can trigger errors
- Replace suspect sensors incrementally—not all at once—to avoid unnecessary expense or failure
- Re-clean, secure, and protect connectors to prevent recurrence, and confirm readings post-repair
An operator faced intermittent speed loss and F654/F658 codes that reoccurred after cleaning the joystick switch. Back-probing showed correct output voltage at the switch, but readings dropped at the TCU connector. Tracing the harness revealed a pin misaligned in a sealed multiplug. Reseating the pin restored voltage continuity; the dozer ran smoothly all week afterward with no further codes.
In summary, the 750C II’s speed-control issues often trace back to electrical signal integrity—either through bad voltage, misaligned sensors, or wet/corroded connectors. Systematic voltage checks, harness tracing, and protecting connections against moisture dramatically improve reliability and reduce needless parts replacement.