Citroën DS4 Trunk Sensor Repair Guide: How to Fix False Messages

Introduction to the Trunk Sensor Problem in the DS4

The Citroën DS4 is known for its sophisticated design, but some owners face an annoying problem: the “open trunk” warning on the dashboard, even when the trunk lid is properly locked. This error is not just visual. It prevents the doors from being locked via the remote control and keeps the interior lights on, which can drain the battery if the car is left parked for a long time.

This symptom usually indicates a failure in presence sensorIn the DS4, this is integrated into the locking mechanism. Unlike older cars that used a visible push pin, modern models use an internal microswitch. When this component fails, the vehicle’s communication network receives incorrect information, generating false alerts.

Symptoms and Technical Diagnosis

Before disassembling any part, it’s important to identify whether the fault is actually in the sensor or if there’s a general electrical malfunction. The most common symptoms include:

• The message “Trunk open” flashes on the center display.
• Audible warning signal when passing over potholes or irregularities in the road.
• The alarm cannot be activated because the system interprets it as the car being vulnerable.
• The courtesy light in the luggage compartment remains on even when the car is locked.

For an accurate diagnosis, an automotive scanner is used to check the DTCs (Direct Trouble Codes)These are fault codes recorded by the onboard computer. In the case of the locking and body system, the codes usually begin with the letter B (Body/Carroceria). A common code is… B1713, which indicates a fault in the trunk locking contact signal.

Main Causes of Error

There are three main causes for this problem in the DS4:

1. Worn micro-switch: The small switch inside the lock suffers from mechanical wear or internal oxidation.
2. Broken wiring in the rubber accordion: With the opening and closing motion of the lid, the wires that pass through the upper fold (near the top) can break internally.
3. Poor connection at the connector: Water infiltration (common after pressure washing) can oxidize the lock pins.

Related Fuses

Before replacing expensive parts, check the integrity of the fuses. In the DS4, the main fuse box is located in the dashboard (driver’s side) and in the BSM (engine service box). Although there isn’t a dedicated fuse for the sensor, the central locking and lighting system depends on this fuse. F7 of approximately 20A in the BSI (intelligent service box inside the cockpit). If the side door locks also don’t work, the problem may be this fuse.

Step-by-Step Repair Guide

To resolve the problem, follow this verification and maintenance checklist:

Necessary Tools

• Torx T20 and T30 keys.
• Plastic spatula for removing finishes.
• Multimeter (for continuity testing).
• Electrical contact cleaner.

1. Wiring Inspection

Open the trunk and locate the rubber gasket in the upper left or right corner that connects the trunk lid to the roof. Gently pull the gasket to expose the wires. If you find any conductors with broken plastic insulation or a split wire, solder them and protect them with electrical tape or heat-shrink tubing (plastic tubing that shrinks with heat to seal connections).

2. Removing the Lock

To access the sensor, you will need to remove the inner plastic trim of the trunk lid. Use the plastic spatula to release the clips without breaking them. After removing the trim, loosen the Torx T30 screws that hold the metal lock. Disconnect the electrical plug by pressing the safety latch.

3. Sensor Testing and Cleaning

With the lock in hand, apply plenty of contact cleaner inside the mechanism and on the plastic connector. Often, the accumulation of dust and dried lubricant prevents the sensor from closing the circuit. Use a multimeter in continuity mode (the mode that beeps) and check if the signal changes when simulating closing the lock with a screwdriver. If the multimeter does not react, the internal microswitch is dead.

Parts and Reference Codes

If cleaning doesn’t solve the problem, replacing the entire lock assembly is necessary, as the sensor is shielded inside the part. The OEM (Original Equipment Manufacturer) reference code for the Citroën DS4 is usually… 8719F8 or variations depending on the year of manufacture.

There are alternative brands on the aftermarket that offer good value for money. Just make sure the part has the standard 4-pin connector for the PSA (Peugeot Société Anonyme) system.

Estimated Costs in Brazil

Prices may vary depending on the region and origin of the item.

When should you seek a specialist?

If the problem persists after replacing the lock, the issue may lie with… BSI (body control unit). The BSI is the brain that manages the electrical system. In these cases, it is necessary to take the vehicle to a workshop that has the original software. Diagbox to reset the parameters or check for any advanced grounding faults.

Conclusion

Repairing the DS4 trunk sensor is considered to be of low to medium complexity. Most of the time, a simple cleaning of the contacts or fixing broken wires in the trunk lid hinge resolves the issue. Keeping the mechanism lubricated with white lithium grease prevents the sensor from seizing and prolongs the lifespan of the electronic components in the trunk system.

Disclaimer

This article is for informational and reference purposes only. The content published here was compiled from publicly available technical information and general market references, and does not, under any circumstances, replace the diagnosis and intervention of a qualified mechanic or authorized dealership. The website is not responsible for any damages, losses, or consequences arising from the practical application of the guidelines described here. Always confirm part numbers, torque specifications, and procedures in the manufacturer’s official manual before any repairs.