What is Kobelco SK200-8 Fault Code B073?

Fault Code B073 on the Kobelco SK200-8 excavator indicates a malfunction in the air conditioning (A/C) evaporator temperature sensor circuit. This code is triggered when the Electronic Control Unit (ECU) detects an abnormal voltage signal from the evaporator temperature sensor, which monitors the cooling coil temperature inside the cabin's HVAC system. While this fault doesn't directly affect engine or hydraulic performance, it compromises operator comfort and can indicate broader electrical issues in used machines. The sensor's primary function is to prevent evaporator icing and maintain optimal cabin climate control—critical for operator productivity during long shifts in extreme conditions.

Common Symptoms

• A/C system failure: The air conditioning compressor may cycle erratically or fail to engage completely, resulting in no cooling.
• Warning light activation: The machine's diagnostic warning lamp illuminates on the instrument panel, indicating a system fault.
• Intermittent cooling: The A/C may work sporadically, particularly when the machine vibrates or operates on uneven terrain.
• No temperature regulation: Cabin temperature becomes difficult to control, with the system blowing only ambient-temperature air.
• ECU fault storage: The code remains stored in memory even if symptoms are intermittent, requiring diagnostic tool access for confirmation.

Potential Causes

The most common technical reasons for Code B073 on used SK200-8 excavators include:

• Sensor failure: The evaporator temperature sensor itself has degraded due to age, moisture exposure, or thermal cycling.
• Wiring harness damage: Chafing or rubbing of the sensor harness against metal surfaces near the evaporator housing—a known wear point in older Kobelco machines.
• Connector corrosion: Water intrusion into the sensor connector terminals, causing increased resistance or open circuits.
• Poor ground connections: Corroded or loose ground points in the cabin electrical system affecting sensor voltage reference.
• ECU communication issues: Rarely, internal ECU faults or software glitches may misinterpret sensor signals.

How to Troubleshoot and Fix Code B073

Step 1: Connect Diagnostic Software Use Kobelco-compatible diagnostic software (or a universal OBD diagnostic tool) to confirm Code B073 is active. Check for additional codes that might indicate related electrical problems. Clear the code and attempt to reproduce the fault during A/C operation.

Step 2: Inspect the Evaporator Temperature Sensor Locate the sensor on the evaporator core inside the cabin HVAC unit (typically behind the dashboard). Visually inspect the sensor wiring harness for obvious damage, particularly where it routes near sharp edges or moving components. Check the connector for corrosion, pushed-back pins, or moisture. Clean terminals with electrical contact cleaner if needed.

Step 3: Test Sensor Resistance and Voltage Disconnect the sensor connector and measure resistance across the sensor terminals using a digital multimeter. Compare readings to Kobelco specifications (typically 2-3 kΩ at room temperature for NTC thermistors). Check for voltage supply at the harness connector—should read approximately 5 volts with ignition on. If voltage is absent, trace wiring back to the ECU for breaks or shorts.

Step 4: Verify Ground Circuits Test continuity between the sensor ground wire and chassis ground. High resistance (above 1 Ω) indicates corrosion or loose connections. On used excavators, ground points often corrode under floor mats or near battery terminals—clean and tighten all related grounds.

Step 5: Replace Components as Needed If the sensor tests faulty, replace it with a genuine Kobelco or OEM-equivalent part. For harness damage common in high-hour machines, repair wiring using heat-shrink solder connectors and reroute away from abrasion points. After repairs, clear codes and run the A/C system through multiple cycles to confirm the fix.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number and seek professional assistance for complex electrical diagnostics or if unfamiliar with excavator systems.