Engine-CodesMercury – B2871 Mercury

B2871 Mercury Code - Left Rear Tire Pressure Sensor Fault

Quick Answer

The B2871 diagnostic trouble code (DTC) for Mercury vehicles specifically refers to a fault detected in the left rear tire pressure sensor. Common causes include Failed left rear tire pressure sensor, Malfunctioning TPMS module, Damaged wiring harness connecting the sensor to the module. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
B2871 Mercury indicates Left Rear Tire Pressure Sensor Fault.
Common causes
Common causes include Failed left rear tire pressure sensor, Malfunctioning TPMS module, Damaged wiring harness connecting the sensor to the module.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Table of contents Created and updated by William Orellana on Sep 12, 2024
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Code B2871 Mercury Description

The B2871 diagnostic trouble code (DTC) for Mercury vehicles specifically refers to a fault detected in the left rear tire pressure sensor. This sensor is a crucial component of the tire pressure monitoring system (TPMS), which is designed to alert the driver when tire pressure is significantly low. When this code is triggered, it indicates that there is an issue with the left rear tire pressure sensor, potentially leading to inaccurate tire pressure readings or a complete failure of the sensor.

OBDII Code B2871 Mercury - Left Rear Tire Pressure Sensor Fault
B2871 Mercury Code - Left Rear Tire Pressure Sensor Fault

Common Causes of B2871 Mercury

  1. Failed left rear tire pressure sensor
  2. Malfunctioning TPMS module
  3. Damaged wiring harness connecting the sensor to the module
  4. Improperly mounted or damaged left rear tire

Symptoms of B2871 Mercury

  1. TPMS warning light illuminated on the dashboard
  2. Inaccurate tire pressure readings displayed on the instrument cluster
  3. Loss of communication with the left rear tire pressure sensor
  4. Increased tire wear on the left rear tire

How to Fix B2871 Mercury

  1. Use a TPMS tool to diagnose the specific issue with the left rear tire pressure sensor.
  2. Replace the faulty sensor with a new one that is compatible with the vehicle.
  3. Check and repair any damaged wiring harnesses or connections.
  4. Reset the TPMS system to clear the fault code and recalibrate the sensors.
  5. Perform a manual inspection of the left rear tire to ensure proper mounting and condition.

Cost to Fix B2871 Mercury

The typical repair costs for addressing a left rear tire pressure sensor fault can vary depending on the specific cause of the issue and the parts and labor required for the repair. In general, replacing a tire pressure sensor can cost between $50 and $200 per sensor, not including labor costs which can range from $50 to $100 per hour. Additional costs may apply if wiring harness repairs or TPMS module replacement are necessary. It is advisable to consult with a trusted auto repair shop for a more accurate estimate based on your vehicle's make and model, as well as the local labor rates in your area.

Tech Notes for B2871 Mercury

When the tire pressure warning light comes on solid and message center displays LOW TIRE PRESSURE, check the air pressure of all tires and adjust to the specified cold pressure listed on vehicle certification label (found on drivers door or door pillar). Drive the vehicle at 20 mph (32 km/h) for at least 2 minutes. If the vehicle has been stationary for more than 30 minutes, a TPM sensor Activation procedure may be needed. When the tire pressure warning light flashes for 70 seconds and then remains illuminated, after bulb-check has been performed and message center displays warning messages, there is a malfunction in the TPM system.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about B2871 Mercury Code

1. What does the OBDII code B2871 mean for a Mercury vehicle?

The code B2871 indicates a fault with the left rear tire pressure sensor, meaning it’s not transmitting data correctly or is malfunctioning.

2. What are common symptoms of the B2871 code in a Mercury?

Symptoms may include a tire pressure warning light on the dashboard, inaccurate tire pressure readings, or no reading for the left rear tire.

3. What causes the B2871 code to appear?

Causes can include a dead sensor battery, a damaged tire pressure sensor, interference with the signal, or a problem with the vehicle's TPMS module.

4. Can I drive my Mercury with the B2871 code?

Yes, but it’s not recommended to ignore it since you won’t receive accurate tire pressure readings, which could lead to unsafe driving conditions.

5. How do I fix the B2871 code on a Mercury?

The most common fix is to replace the left rear tire pressure sensor. Make sure the new sensor is properly programmed and calibrated.

6. How is the B2871 code diagnosed?

A mechanic will use a TPMS scan tool to check the functionality of the left rear sensor and verify if it's transmitting data correctly.

7. How much does it cost to repair the B2871 code?

Replacing a tire pressure sensor typically costs between $50 and $200, depending on the sensor and labor charges.

8. Can a dead sensor battery cause the B2871 code?

Yes, a dead battery inside the tire pressure sensor is a common cause of this code.

9. Do I need to replace all four sensors if one has failed?

Not necessarily. However, if the other sensors are old, it might be a good idea to replace them to avoid future issues.

10. Will resetting the TPMS clear the B2871 code?

Resetting the TPMS may temporarily clear the fault, but if the left rear sensor is defective, the code will likely return.

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