Roof Sensor Fault on an Audi R8 Convertible
- Ryan Brown
- Jul 22, 2025
- 5 min read
Today at REWIRED C&C, we investigate a faulty convertible roof on an Audi R8.
The Issue
This car came to us because its convertible roof would not close properly. The roof moved smoothly, unfolding and tucking away in the back effortlessly. However, when it came to closing, the felt "bat ear" sections, besides the rear screen, that lock over the rear lid would not go into position.
These rear sections of the roof raise out of the way to allow the rear hood to close. Once that stage is completed, these rear felt sections then lock on top. Without this working correctly, the rest of the closing sequence was hindered.
The Investigation
With the actuators moving correctly and no visible loss of hydraulic pressure, it became apparent that a sensor was likely not functioning properly. With no fault codes registered on the car, we had to carefully walk through the closing sequence, monitor which switches are triggered when, and rule out possible suspects. Clearances between sensors and their mating surfaces were also compared on each side of the roof, ensuring that a working sensor was not misreading due to a loose mechanism.
We noticed that the rear lid didn't seem to lock into place once it was closed. With no obvious way to watch the mechanism from within once the lid is down (no viable access panels reveal this area), we carefully placed a phone inside to record the mechanism from a safe location. And as we expected, the lid was not latching - The hooks that engage with the lid did not move.
We now needed to work out why this was occurring. This is a crucial step in the closing sequence, and something was obviously stopping it. Using a careful ear, we noticed that we could still hear the rear lid hydraulics trying to move. This suggested that it was not so much that the latch was not energising, but rather that the car was still "lowering" the rear lid, as far as the car was concerned.
This revealed that the car was stuck in the lid-closing stage, constantly trying to lower the lid hydraulically. This made sense as if the car believes the rear panel is still up, it won't stop trying to close, latch, or lower the "bat ears" until it thinks it has reached the required closed position. There were sensors on the latch itself, but these seemed more related to the latching position, not whether the lid had gone fully down.
The next step included investigating the rear lid mechanism, more specifically, the sensors at each end of the hydraulic ram. These sensors monitor the position of the lid through the hydraulic ram, registering if the upper and lower limits have been met. Fortunately, there are only sensors on the passenger side ram, reducing the number of sensors to test.
Investigating the wires, there were no visible breaks. This is a crucial step as we generally find more broken wires to sensors than actual broken sensors when working on most convertible cars. The reason for this is that cables consistently bending at tight radii can begin to strain and weaken their insulators and conductors, producing weak points in the wires and raising the risk of breaking. This problem is also extremely common on most boot hinge and door wiring too.
With the sensors being found tightly in place, with no signs of wear or play, we deduced that the sensors themselves were the most likely culprit. After further testing and experimentation, and everything else appearing to work as expected, we concluded that the right course of action was to acquire and replace the sensor.
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The Repair
The repair was a little tricky, but nothing compared to some issues we've faced with convertibles in the past.
Available as a pair, the customer agreed that it would be best to change both sensors, ensuring that both are new and in working order. Unfortunately, there were some complications.
The new sensors came with a plug. The plan was to connect a new sensor in place of the original, and definitively verify that the sensor was the cause before proceeding further. However, the original wiring on the car did not include a plug, with the original wiring permanently attached using a crimped joiner. This meant that we had to cut off the new plug and solder the wires in place.
The other annoyance was due to the wiring colours. Each sensor had a brown wire, then a yellow wire on the other side. The way the wire colours matched the car was not intuitive, as the brown wire of the car did not join with the brown wire of the switch.
Even though the car side of the connection still had a brown wire, the secondary colour was different depending on which side of the mechanism the wires connected to. Additionally, the other coloured wires on the switches did not match the wire on the car either. As shown in the picture below, a brown wire is joined to a white wire, while the other brown wire is connected to a yellow.
Fortunately, the colours on the new sensors matched their respective counterparts. This allowed us to place the new sensor into the mechanism and make the new connections one at a time. Yellow to brown, and brown to white, etc. This would ensure that the wires are cut to the right length, with enough slack, and that there is no accidental mix-up of the sensor's polarities or which set of wires a particular replacement connects to.
The wires were soldered together with black heatshrink tubing insulating the connections. This black insulation also contained a glue to further reinforce the connections, but also to make it waterproof, preventing moisture or water running off the roof from affecting the connections over time. The result was a clean, strong join, much thinner than with the original clear/white insulation. As these connections are made along a straight, static section of the wiring harness, there was no concern about the heatshrink or solder having to move or bend.
A clean, white towel was placed over the boot interior to protect it from solder, heat, glue, tools, or any other possible risk of damage. A folded section of tinfoil was used as a heat deflector to aid in heat shrinking the sleeving to size and to protect the towel from burns. This method is also very beneficial when heat gunning in tight areas, as it protects the work area while also reflecting the heat towards the heat shrink where the gun cannot reach. However, be warned that the foil can heat up quickly, potentially reaching a temperature high enough to melt into a wire or plastic if it were to accidentally touch.
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The Result
The original wiring was held in place by cable ties, which had to be cut to expose the connections and fit the new sensors. Due to the risk of loose wires getting caught in the mechanism, the new wiring was temporarily taped into place to verify its fit and to test the movement of the mechanism. Once ready, the roof was tested and it closed perfectly first time. Once tested a few times, fully open and then fully closed, we replaced the cut cable ties and put the rear back together before final testing.
