John Deere 174.03 – Engine Control Unit (ECU): Fuel Temperature High Signal Voltage

The Engine Control Unit (ECU) has detected a voltage from the fuel temperature sensor that is higher than the normal operating range. This indicates an abnormal reading from the component responsible for monitoring fuel temperature, which can be caused by a faulty sensor, damaged wiring or connectors, or an internal ECU issue. The ECU relies on accurate fuel temperature data to make precise adjustments to fuel injection for optimal engine performance and efficiency.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5065M
• 5075M
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5095M
• 5095MH
• 5105M
• 5015ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5E Series
• 5M Series
• 6000-9000 Series
• 6120
• 6420
• 7230
• 8100-8530
• 9230-9630
• CTS
• 9650 STS
• S-Series
• S550-S770
• 310G/J
• 410G/J
• 444J
• 544J
• 624J
• 135D
• 250GR
• 450DLC
• 748H
• 250D
• 370E
• 460E

1. 1

   Inspect the wiring harness leading to the fuel temperature sensor for open circuits, shorts to power (e.g., 12-volt short), or physical damage.

2. 2

   Check the harness 'flex' point approximately 24 inches back from the sensor connector for broken wires inside the insulation or corroded pins caused by fan blast and engine heat.

3. 3

   Test the sensor output voltage using a multimeter or diagnostic tool to verify if it is exceeding the 4.9V threshold.

4. 4

   Check for related codes (such as 620.03) that might indicate a broader 5V reference or sensor supply voltage issue.

1. 1

   Locate the Sensor

   Find the fuel temperature sensor. On many John Deere engines, it is located on the injection pump (towards the rear, close to the last injection line barrel) and is often retained by a round silver nut. On common-rail engines, it may be located on the fuel rail or fuel filter housing.

2. 2

   Disconnect the Harness

   Carefully unplug the connector from the sensor.

3. 3

   Inspect and Clean

   Check the connector pins for corrosion or debris. Clean if necessary.

4. 4

   Repair Wiring (If Applicable)

   If you found a broken wire or short during diagnostics, splice and repair the wiring harness using heat-shrink connectors to protect against moisture.

5. 5

   Replace the Sensor (If Faulty)

   If the wiring is intact but the sensor is outputting out-of-range voltage, unscrew the sensor and replace it with a new OEM unit. Be careful not to overtighten, as it usually seals with an O-ring.

6. 6

   Clear Codes and Recalibrate

   Turn the key switch to the ON position, use a diagnostic tool (like John Deere Service ADVISOR) to clear the stored 174.03 code, and reset the ECU to ensure it accurately processes the new signals.