JCB P0173 – ECU1: Steering Angle Sensor Over Range

The steering angle sensor signal is outside of its expected minimum or maximum values, making the reading implausible to the control module. This fault typically affects machines equipped with multi-mode steering systems (such as Quadtronic four-wheel steering), resulting in the machine being unable to change between steering modes or getting stuck in a single mode.

• 2000 Series
• 2155
• 2170
• 3000 Series
• 525
• 526-56
• 527
• 527-58
• 530
• 531-70
• 532
• 535
• 535-95
• 535-140
• 536-70
• 537
• 540
• 540-140
• 550
• 550-80

1. 1

   Visually inspect the steering angle sensors and their wiring harnesses on both the front and rear axles for physical damage, corrosion (especially from road salt or fertilizer), or loose connections.

2. 2

   Check that the sensor is securely mounted and has not been knocked out of position.

3. 3

   Verify power and sensor signal at the sensor's connector (typically a three-wire proximity switch). If equipped, check if the small LED indicator light on the back illuminates when activated (i.e., when metal is in front of it), which can confirm if the sensor is powered and detecting its target.

4. 4

   Check sensor alignment and air gap. Ensure the target, which is often a pin or plate on the steering linkage, is not bent or misaligned. For some black plastic sensors, the air gap should be approximately 1-2 mm.

5. 5

   Perform a basic hydraulic system check to ensure fluid levels are correct and fluid is clean, as hydraulic issues can sometimes present as control system faults.

6. 6

   Use a JCB-compatible diagnostic tool (like JCB Service Master) to read live data from the steering angle sensor as you turn the steering wheel. A smooth, progressive change in the reading indicates a functioning sensor, while spikes or drop-offs suggest a dead spot or failure.

1. 1

   Ensure machine safety

   Park the machine on firm, level ground, lower all attachments, and engage the parking brake before working on the steering system.

2. 2

   Clean and adjust sensor

   Clean any dirt or debris from the sensor and its target. If the sensor is adjustable, set the correct air gap. For some threaded metal sensors, screw the sensor in or out until the indicator LED lights up, then give it a final quarter-turn towards the target.

3. 3

   Test sensor function

   With the machine on, have an assistant slowly turn the steering wheel from lock to lock. Observe the sensor's LED (if equipped) to ensure it activates and deactivates as the target passes it. Alternatively, use a multimeter to check for a change in the signal wire's output.

4. 4

   Attempt recalibration

   On some machines, a steering sensor calibration or reset may be required after sensor replacement or adjustment. A generic procedure involves turning the ignition on (without starting the engine), slowly turning the steering wheel fully to the left, then fully to the right, and returning to center. However, many modern JCB machines require a diagnostic laptop with appropriate software to perform a proper calibration.

5. 5

   Replace the sensor

   If the sensor is confirmed to be faulty (no signal, erratic signal, or internal failure), disconnect the wiring harness, unbolt the sensor from its bracket, and install the new part.

6. 6

   Inspect wiring harness

   If a new sensor does not resolve the issue, check the wiring harness between the sensor and the control module for continuity and for shorts to power or ground on the signal, power, and ground wires. Pay close attention to areas where the harness may rub or bend.