Strain Gauge Fault

[MikePhua]

It all began when the strain gauge on a Manitou 1840 telehandler began showing erratic readings, eventually resisting calibration altogether. The operator observed error codes tied to the machine’s control modules—signals that something deeper was amiss. At the heart of it lies a deceptively simple yet critical component: the strain gauge, positioned on the rear axle, designed to detect the bending of the axle under load. When rust forms beneath its contact surface—despite supposed sealing—it distorts readings by applying uneven pressure, suggesting a heavy load even when there is none.
Machine Origins and Brand Legacy
Manitou’s story starts in 1958 in Ancenis, France, with Marcel Braud’s ingenious idea: invert a tractor’s layout, add a lifting mast and hydraulic steering, and you have a rough-terrain forklift. The name “Manitou”—easy to say in any language—literally means “handles everything” . This innovation laid the groundwork for a global presence that spans over 60 years, 140 countries, 10 manufacturing facilities, and multiple logistics centers .
The telehandler line emerged in 1981 with the “Maniscopic” series. By the early 1990s, rotating telehandlers, aerial work platforms, and truck-mounted forklifts diversified their offering. Strategic acquisitions—Gehl in 2008 and Terex’s Indian operations in 2017—bolstered global reach and product range .
Model Overview Specs
The Manitou MT-1840 stands as a robust mid-range telehandler with these specifications:

• Maximum lift capacity: 4,000 kg
  
• Maximum boom height: 17.55 m
  
• Maximum outreach: 13.08 m
  

Additional performance data includes:

• Break-out force: 7,900 daN
  
• Cycle times (lifting ≈ 17.3 s, lowering ≈ 12.7 s, extending ≈ 16.1 s, retracting ≈ 15.6 s)
  

Its modern “Easy” variant offers similar capacities with a slightly smaller engine, plus enhanced attachment flexibility via the Easy Connect System .
Glossary of Key Terms

• Strain Gauge: A sensor that measures deformation (in this case, axle bending under load).
  
• Calibration: Re-establishing baseline sensor readings to ensure accuracy.
  
• Error Codes (DTCs): Diagnostic codes stored by onboard computers alerting to inconsistencies or faults—for example, strain gauge inconsistency flags the sensor or its reading.
  
• Control Modules (MMI, MP1, MP2): Electronic units overseeing interface, machine operations, or hydraulics.
  
• Break-out Force: Resistance the attachment can overcome when prying or digging.
  

Real-World Anecdote
Consider a site operator named Rachel who noticed her MT-1840’s display showing odd axle-load values. After rinsing and wiping sensors during a rainy shift, the readings fluctuated wildly. She paused operations, disassembled the strain gauge housing, and unearthed surface rust at the contact point. Once cleaned and properly resealed, the gauge returned to normal, restoring accurate load readings—and with it, operator confidence.
Solutions and Recommendations

1. Clean the strain gauge:
   • Remove the sensor, thoroughly clean its contact surface and the mating area.
     
   • After cleaning, apply RTV sealant or thread-lock to prevent moisture intrusion—Moisture under that tiny metal slice can skew results dramatically .
     
2. Recalibrate properly:
   • Enter “reset strain gauge” via the machine’s service menu.
     
   • Follow sequential steps: fully extend stabilizers, raise and retract the boom, fully lower the boom, then lift stabilizers again with a load attached (minimum half-rated capacity) .
     
   • Only perform this procedure on flat ground, ideally at cool axle temperature (< 50 °C). The display will confirm each stage—failure at any stage aborts the process .
     
3. Monitor error codes:
   • Inspect codes like “A20000” (strain gauge inconsistency) or “820002–005” variations, which indicate ongoing issues with the strain circuitry .
     
4. Adhere to safety protocols:
   • Only trained technicians should disassemble or calibrate these sensors—errors may trigger warnings or lockouts .
     
   • Always park on level ground, shut down power, and follow lockout procedures.
     
5. Prevent recurrence:
   • Include sensor inspection in regular maintenance (e.g. every 50 hours or at service intervals).
     
   • Document cleaning dates and calibration completions in the service log.
     

Additional Technical Advice

• Ensuring stabilizer movement is fully detected—partial contact may prevent calibration from completing.
  
• Use accurate weights for calibration (half-load is a common requirement).
  
• Replace sensors if cleaning fails to restore normal readings—contact experienced hydraulic/electrical service providers.
  
• Keep firmware/software of control modules up to date to enhance sensor communication reliability.
  

Conclusion
A malfunctioning strain gauge on the Manitou MT-1840 often boils down to deceptively simple causes—like rust under a poorly sealed contact point—but clarity comes through methodical cleaning, careful calibration, and attention to detail. By understanding the machine’s history, sensor functions, and how calibration sequences unfold, operators and maintenance crews can restore precise load detection. The result is safer, smoother operations and a machine that truly “handles everything,” just as its name promises.