What is Komatsu D85PX-15 Fault Code E-22?

Fault Code E-22 on the Komatsu D85PX-15 bulldozer indicates a transmission oil temperature sensor circuit malfunction or abnormally high transmission oil temperature. This code is triggered when the Electronic Control Module (ECM) detects either an out-of-range signal from the transmission temperature sensor or when actual transmission fluid temperatures exceed safe operating thresholds (typically above 120-130°C or 248-266°F).

This fault is critical for the D85PX-15 because excessive transmission heat can cause premature clutch pack failure, seal degradation, and reduced hydraulic oil viscosity. The transmission system relies on precise temperature monitoring to protect the torque converter and planetary gear sets from thermal damage. Ignoring this code on used machines can lead to catastrophic transmission failure requiring complete rebuilds costing $15,000-$25,000.

Common Symptoms

• Transmission temperature warning light illuminated on the instrument panel (red or amber indicator)
• Reduced power output or machine entering derate mode, limiting engine RPM to 1,200-1,500 to protect drivetrain components
• Sluggish shifting between gears or delayed engagement when changing direction
• Audible warning alarm sounding intermittently or continuously during operation
• Visible steam or burnt oil smell emanating from the transmission housing area

Potential Causes

The most common technical causes for E-22 on used D85PX-15 machines include:

• Failed transmission temperature sensor (thermistor-type sensor located in the transmission case) due to internal element degradation
• Damaged or corroded wiring harness at the sensor connector—particularly at the harness routing point near the left track frame where vibration causes wire chafing
• Low transmission oil level causing inadequate cooling and actual overheating conditions
• Clogged transmission oil cooler with debris, mud, or deteriorated cooling fins reducing heat dissipation efficiency
• Faulty ECM ground connections creating erratic voltage readings that trigger false codes
• Worn torque converter or slipping clutches generating excessive heat beyond sensor fault issues

How to Troubleshoot and Fix Code E-22

Step 1: Verify Actual Transmission Temperature Start the machine and allow it to reach operating temperature. Using an infrared temperature gun, measure the actual transmission case temperature near the dipstick. Compare this to the displayed temperature on the monitor. If readings differ by more than 10°C, suspect a sensor or wiring issue rather than actual overheating.

Step 2: Inspect the Temperature Sensor and Harness Locate the transmission temperature sensor on the left side of the transmission case (typically a two-wire sensor with a gray connector). Disconnect the harness and inspect for:

• Corrosion on connector pins (common on used machines operating in wet conditions)
• Oil contamination inside the connector indicating a leaking sensor seal
• Damaged wiring insulation at the frame routing point approximately 8 inches from the sensor

Step 3: Test Sensor Resistance Using a digital multimeter, measure the sensor's resistance. At 20°C (68°F), resistance should read approximately 2,200-2,800 ohms. At 80°C (176°F), it should drop to 280-320 ohms. Values outside this range confirm sensor failure. For used excavators, always check the harness continuity back to the ECM connector C42 (pins 18 and 32) for opens or shorts to ground.

Step 4: Check Transmission Oil Level and Cooler Verify transmission oil is at the proper level on the dipstick (check with machine level and oil at operating temperature). Inspect the transmission oil cooler (located behind the hydraulic oil cooler) for blockages. On high-hour used machines, remove and reverse-flush the cooler with solvent to restore flow.

Step 5: Clear Code and Monitor After repairs, use Komatsu diagnostic software (KOMTRAX or dealer-level tools) to clear the fault code. Operate the machine under load for 30 minutes while monitoring transmission temperature. If E-22 returns immediately, suspect ECM calibration issues requiring dealer-level software updates.

Disclaimer: This guide provides general troubleshooting information. Always consult the Komatsu D85PX-15 service manual and consider professional diagnostic assistance for complex electrical issues or transmission repairs. Improper diagnosis can lead to unnecessary component replacement or further machine damage.