Engine Management Light on a Range Rover Sport: How We Traced It to an Intermittent AdBlue Sensor Fault (Colchester Case Study)
A 2018 Range Rover Sport arrived at our Colchester workshop with the engine management light illuminated. An initial diagnostic scan identified an AdBlue level fault stored within the engine control module. Interestingly, there was no AdBlue countdown displayed on the dashboard, and the customer confirmed that the vehicle was still showing over 2,000 miles of remaining range.
Live Data Reveals the Real Problem
Using our dealer-level diagnostic equipment, we accessed the live data from the engine control module and found something unexpected. While the dashboard indicated the AdBlue tank contained sufficient fluid, the engine control module believed the tank was completely empty. This discrepancy immediately suggested that the issue was not simply low AdBlue, but a fault within the level monitoring system.
To investigate further, we added approximately three litres of AdBlue. The live data changed, but only to indicate around eight litres in the tank, while the dashboard display remained unchanged. This inconsistent behaviour reinforced our suspicion of an intermittent fault rather than a straightforward fluid level issue.
Oscilloscope Testing Confirms a Sensor Fault
Electrical testing was then carried out, including power supply and earth checks, followed by oscilloscope testing of the AdBlue level sensor signal. The wiring diagram identified the circuit as a pulse-width modulation (PWM) signal. After confirming the expected waveform characteristics, we monitored the signal while refilling the AdBlue tank. During this process, the oscilloscope captured intermittent signal corruption, clearly indicating an internal failure of the tank level sensor.
The Repair: AdBlue Tank Assembly Replacement
The AdBlue tank assembly was replaced, as the level sensor is integrated into the unit. Following installation, we repeated the oscilloscope tests while filling the new tank and confirmed a clean, consistent waveform with the expected signal changes. Diagnostic data and vehicle operation were then verified, confirming the fault had been successfully rectified.
Why This Case Matters: Diagnostics Over Guesswork
This job is a good illustration of why proper diagnostic procedure matters when an engine management light comes on in a modern vehicle like the Range Rover Sport. The stored fault code pointed to AdBlue, but the dashboard told a different story — good range, no countdown warning. Only live data analysis and oscilloscope testing uncovered the real issue: an intermittent AdBlue tank sensor fault.
Simply clearing the code, topping up the AdBlue, or replacing parts based on the fault code alone wouldn’t have fixed this vehicle. It’s exactly this kind of methodical, equipment-led diagnosis that separates a proper repair from a guess.