D5H Dash Lights Problems

[MikePhua]

Machine Overview and History
The Caterpillar D5H is part of Caterpillar’s elevated-sprocket “H-Series” of medium bulldozers, with production roughly between 1985 and 1996. It uses a 7.0 L, 4-cylinder diesel engine producing about 129–132 gross horsepower (≈96–100 kW), and roughly 120 net HP (≈90 kW) depending on year and condition.  The D5H was designed with improved durability via the elevated drive sprocket design, better undercarriage life, and improved operator comfort.
The D5H features a hydraulic system with about 18.5 gallons (≈70 L) of hydraulic oil, pump flow around 28.7 gallons per minute (≈108.6 L/min), and hydraulic pressures up to ~3,000 psi (≈207 bar).  It also has a 12-volt electrical system with a 50-amp alternator in many models.
What the Dash Lights Mean (Terminology & Functions)
The dash—specifically the EMS (Engine Monitoring System) or instrument panel—uses a set of indicator lights (warning or alert lamps). Understanding each light helps diagnose issues. Terms to know:

• EMS Panel: Engine Monitoring System; panel with lamps for various engine, transmission, hydraulic and electrical conditions.
  
• Bake-off test / Panel Test Switch: a switch that checks whether all dash lights are functional by lighting them momentarily.
  
• Sending units / sensors: devices that send electrical signals based on engine temp, oil pressure, etc.
  
• Ground / power circuits: electrical wiring that supplies power (positive) and ground (negative) to lamps and sensors.
  

On the D5H:

• The EMS panel has two vertical columns, each with five lights. However, only certain lights are active or meaningful during normal operation.
  
• On the Left-Hand (LH) column, the functional/important lights are:
  • Top: Coolant temperature warning
  • Center: Engine oil pressure warning
  • Bottom: Hydraulic oil temperature warning
  
• On the Right-Hand (RH) column, the key ones are:
  • Top: Power train oil temperature warning
  • Center: Alternator charge warning
  • Bottom: Power train oil filter warning
  

There are also “dummy” or non-active / “unused” lamp positions that light up only during the panel-test but might not correspond to actual functions.
Common Problems with Dash Lights
Users report several recurring issues:

• Some warning lights stay lit even when conditions are nominal (e.g. hydraulic oil temp high when engine is cold). This suggests either faulty sensors, incorrect wiring, or bad ground.
  
• Lights like the “check alternator” remain on despite having replaced or repaired the alternator, pointing to wiring, fuse or grounding issues.
  
• Broken wires, blown fuses, or corroded connectors are frequent culprits.
  

Diagnostic Procedure
Below is a structured checklist to diagnose dash light problems on a D5H:

1. Battery & Charging System Check
   • Verify battery voltage with engine off and with engine running.
     
   • Inspect alternator output; ensure proper belt tension.
     
2. Fuse / Relay Inspection
   • Find all relevant fuses for EMS, dash lights, sensors. Replace any blown ones.
     
3. Wiring and Connections
   • Inspect wiring harnesses behind dash for breaks, chafing, corrosion.
     
   • Check connector pins; clean contacts.
     
4. Grounding Points
   • Locate known ground points for dash and sensor circuits; clean and ensure tight connections.
     
5. Sensor / Sending Unit Testing
   • For any warning that seems erroneous (engine oil pressure, coolant temp, etc.), test the corresponding sensor: remove it, inspect, measure resistance / output.
     
6. Panel Test Switch
   • Use the “panel test / lamp test” switch (if equipped) to light all lamps. If some lamps do not light during test, likely they are burnt out, lack proper power or have broken wiring.
     
7. Swap Known Good Parts
   • If possible, swap a sensor, lamp, or ground wire with a known good one to see if the issue follows the wiring or stays.
     
8. Check for Fault Codes
   • Though older D5H models may not have modern ECUs, check whether there are any legacy systems (or manual codes) indicating sensor faults.
     

Solutions and Repairs
Based on diagnostics, likely solutions include:

• Replacing faulty sensors (oil pressure, coolant temperature, alternator output).
  
• Repairing or replacing wiring harness sections found damaged.
  
• Ensuring all ground connections are clean, tight, and free of corrosion.
  
• Replacing burned-out or non-functioning light bulbs / bulbs in lamp assemblies.
  
• Replacing fuses, or fuse holders if connections are loose or corroded.
  
• If power source to dash is weak (due to battery or alternator), resolve charging or supply issues.
  

Case Story
A machine operator in Northern Europe had a D5H whose alternator light stayed on despite installing a new alternator. After replacing the alternator, the light still glowed. Following troubleshooting, the cause was a fusible link that had degraded, giving enough voltage to start engine but not enough clean signal to satisfy the alternator charging circuit. Fixing the link and securing the ground connections solved the issue.
Data and Specs Useful for Testing
Below are useful specifications when diagnosing or comparing performance:

• Hydraulic system pressure: ~3,000 psi (≈206.8 bar)
  
• Hydraulic pump flow: ~28.7 gpm (≈108.6 L/min)
  
• Electrical system: 12 V battery, 50 A alternator
  
• Operating weight: between ~21,900 lb to ~27,500 lb depending on version and attachments (≈9,900 kg to 12,500 kg)
  

Preventive Measures
To reduce future dash-light problems:

• Schedule clean-ups of electrical connectors, especially in cab and around engine.
  
• Use dielectric grease on connectors after cleaning to prevent corrosion.
  
• Check fuses regularly, especially after hard use, vibration, or moisture exposure.
  
• Include ground connections in routine inspection.
  
• Use the panel test switch periodically to ensure lights and lamps are functional.
  

Conclusion
Dash lights on the Caterpillar D5H are critical for safe and reliable operation, warning of overheating, low oil pressure, charging, and other systems. Many dash-light issues stem from wiring, ground faults, sensors, or weak power rather than actual system failures. A methodical diagnostic approach, paired with preventive maintenance, often isolates and resolves the problem without major component replacement.