09 January 2023
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D4 parking sensors: When one fails, they all stop working
: credit: © Dave Barker
Changing the outer rear park sensors is a simple job, if you have slim hands and can work blind
Need to know:
Time: 1 hour (bumper on).
Difficulty: 1 out of 5: bumper on; 2 out of 5: removing bumper
Models: Discovery 3 and 4.
Tools needed: General workshop tools including long nose pliers (an assistant with a slim hand and long fingers is helpful).
Parts & costs: Parking Aid Sensor rear, LR038533, from £38 to £127 for a Genuine Land Rover part.
Work safely:
• Wear protective gloves or barrier cream to protect the hands and skin from fluids, oils and sharp edges of components.
• Ensure the vehicle is on level firm ground and prevented from rolling by applying the park brake and selecting a gear while working underneath.
• Place axle stands under the rear of the chassis in case of unexpected lowering of the air suspension.
Contact: Maddison 4x4, Water House Farm, Station Road, Topcliffe near Thirsk, YO7 3SG. 01845 587407, maddison4x4.com.
The Discovery 4 is a long vehicle and when reversing into a parking space or even up to a wall you are thankful for the rear parking aids/sensors telling you just how close to an object you are. When they stop working you quickly discover just how reliant you have become on them, and so there’s a need to get them working again as soon as possible.
Discovery 4s have four rear parking sensors located in the rear bumper, two towards the centre of the bumper and two towards the outside edges. Each sensor is held by two clips into a housing which sits in the rear bumper. They are a simple push-in fit.
Replacing a parking sensor should be a simple job, however, the sensor has to be removed and fitted from inside the bumper. To do this, you really need to remove the complete rear bumper, which requires removing the rear side lights, mudflaps, rear quarter panels, then at least four screws, 12 clips and two bolts – it’s a job that no one likes doing. If you do need to remove the bumper, see our feature on how to do this here.
The 2012 Model Year Discovery 4 seen here was brought into the workshop with the owner complaining that the rear parking sensors had stopped working. Unfortunately, when a single sensor fails, all the other rear park sensors stop working. To discover if it was just a single faulty sensor or more than one, or whether it was a wiring fault, the Discovery needed to be plugged into the diagnostic testing equipment. This showed just one of the four sensors had failed and it was an outside left-hand sensor – oddly, it’s usually this one that seems to fail; maybe it’s more exposed to water from road spray than the rest. The outside sensors can be replaced without removing the bumper, with a bit of twisting of the hand to reach up inside it, saving a lot of time. Once the replacement sensor had been fitted, all the rear parking sensors started working again, and the owner was once again able to reverse confidently.
Diagnosing the problem: A diagnostic tool (or decent code reader) confirms if a single sensor had failed, or if all the sensors had stopped working, meaning a possible electrical fault.
A faulty sensor: The diagnostics confirms the problem is just a single reversing sensor that had stopped working, and that it is the outside left-hand side sensor.
Hidden away: The outer reversing sensors are just accessible without removing the rear bumper assembly, but they are still difficult to reach. Arrow shows approximate position.
It’s difficult to see: Looking up into the bumper it’s possible to see the sensor and how it clips into the housing; also why it can fail because of dirt and water ingress.
Twist and pull: With a lot of twisting and feeling, and a good long reach, the reversing sensor can just be reached and unclipped, releasing it from its bumper housing.
Push out: Now that the sensor is unclipped, it is easily pushed out of its housing from the outside of the bumper.
Disconnect: Here, the sensor is gently teased down, carefully gripping its cable with pliers, until the multi-plug can be disconnected and the sensor removed.
New sensor: After cleaning the wiring harness multi-plug, this new sensor is plugged in, fed back in behind the bumper, aligned with its housing and pushed to clip in.
Working again: The fault code from the failed sensor is cleared and the complete rear system is working again, leaving just this cleaning oil to be wiped from the bumper.
Completely removing the bumper: As you've seen here, the outer rear sensors can be replaced by reaching up with the rear bumper in place. For the inboard sensors it’s necessary to remove the rear bumper. See our feature on how to remove a Discovery 3 bumper here – the principle is similar for Discovery 4.
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