P0871 Fault Code in Land Rover: Causes, Symptoms, and Fixes

This code indicates that the Transmission Control Module (TCM) has detected that the Transmission Fluid Pressure Sensor B is reading a lower-than-expected hydraulic pressure. Essentially, the transmission fluid pressure in that circuit is insufficient, which can lead to improper gear engagement or slipping.

Common Causes:

1. Low or dirty transmission fluid
2. Faulty Transmission Fluid Pressure Sensor B
3. Damaged wiring or connectors in the sensor circuit
4. Internal transmission issues, such as solenoid or clutch wear

Symptoms:

1. Delayed or harsh shifting
2. Transmission slipping
3. Check Engine Light (CEL) or Transmission Warning Light
4. Erratic gear engagement

Diagnostic Steps:

1. Check transmission fluid level and condition; refill or replace if necessary.
2. Inspect wiring and connectors for the TFP Sensor B.
3. Test the sensor using a multimeter or scan tool per manufacturer specs.
4. Monitor live transmission data with a scan tool to confirm low pressure readings.
5. If fluid and sensor are fine, inspect internal transmission components.

Repair:

1. Replace Transmission Fluid Pressure Sensor B if faulty.
2. Repair or replace damaged wiring/connectors.
3. Flush or replace transmission fluid if contaminated or low.
4. Address any internal transmission problems if detected.