A 2018 Range Rover Sport was towed in completely dead on the A24 after the driver reported a burning smell and a sequence of escalating high voltage dashboard warnings. The vehicle, an L494 model in the UK market, had been in the shop just the week prior for a replacement auxiliary battery. When the customer picked it up on Wednesday, she noted it did not feel right, and the vehicle kept prompting her to change the key battery.
By Saturday, the situation escalated. The vehicle had not fully charged. While driving, a message appeared stating 'high voltage fault - safe to drive', accompanied by a distinct burning smell. Halfway home, this changed to 'high voltage fault - do not drive'. The vehicle eventually died on the A24, displaying multiple dashboard failure messages, and refused to move from a junction. The breakdown patrol suspected the power distribution unit, but the workshop had already checked that component during the previous visit and found it fully functional. Installing another new 12V auxiliary battery at the roadside did not resolve the non-start condition.
Decoding the Fault Cascade
The workshop pulled the diagnostic codes and found three critical faults logging across different modules. The Battery Charger Control Module 1 recorded U006487, indicating a missing message on Vehicle Communication Bus E. The Battery Energy Control Module 2 logged U300600 for Control Module Input Power A with no sub-type information, alongside P0A9513, indicating High Voltage Fuse A had an open circuit.
In our own data, seeing a primary high voltage fuse code mixed with communication errors usually points to a severe upstream failure. The combination of P0A9513 and the customer's report of a burning smell before the total loss of propulsion is a definitive indicator of a catastrophic failure within the high voltage system.
Pinpointing the Internal Short Circuit
The diagnostic engine ranked a High Voltage System Internal Short Circuit or Component Failure as the primary cause, assigning it a 95 percent probability with a high severity rating. An internal short circuit within a major high voltage component, such as the electric drive motor, the high voltage AC compressor, or the traction battery pack itself, would cause the main high voltage fuse to blow.
Once that fuse blows, it physically disconnects the high voltage system. This immediate loss of high voltage power results in the vehicle's non-start condition, the complete loss of propulsion, and the 'do not drive' warning. The recommended approach here begins with a strict High Voltage Isolation Procedure, followed by a direct HV Fuse Inspection. Technicians must then perform an Insulation Resistance Test of the high voltage components and a thorough visual inspection of the wiring to locate the exact source of the short.
Assessing the Junction Box and Contactors
A short circuit severe enough to blow the main fuse and create a burning smell often causes collateral damage. The system flagged a damaged High Voltage Junction Box or Traction Battery Contactor Assembly as the second most likely cause, at 85 percent probability.
These components are integral to power distribution and safety. A severe electrical event can cause significant thermal damage. Technicians need to inspect the junction box and contactors for melted plastic, scorched busbars, or carbon tracking. Such damage directly leads to the main fuse blowing. Repairing the primary fault will likely require replacing these components if the thermal event compromised their physical integrity. The required tests include the High Voltage Isolation Procedure, an HVJB Inspection, and a Traction Battery Contactor Inspection.
The Low Voltage Starvation Problem
The rapid depletion of the 12V system explains why the vehicle died completely and why throwing another new auxiliary battery at the problem did not help. The diagnostic ranked a Failed DC/DC Converter at 75 percent probability.
The DC/DC converter converts high voltage from the traction battery to low voltage to charge the auxiliary battery and power the standard electrical systems. When the main high voltage fuse blows, it starves the DC/DC converter. Without a functional converter, the 12V auxiliary battery depletes rapidly under the load of the vehicle's systems. This leads to a cascade of low voltage conditions and communication errors across virtually all control modules, resulting in a non-start condition regardless of the auxiliary battery's actual health. Technicians should verify this by performing a DC/DC Converter Power and Ground Check, along with an Output Voltage Test, after isolating the high voltage system.
Investigating the Battery Energy Control Module
Finally, the diagnostic highlighted a damaged Battery Energy Control Module or its power circuitry at a 65 percent probability. The U300600 code directly indicates an issue with the 12V power supply to this module.
The module is the central controller for the high voltage battery, managing health, state of charge, temperature, and the main high voltage contactors. The power supply issue could stem from physical damage caused by the thermal event, or a problem with the wiring harness such as high resistance or an open circuit. A malfunctioning control module cannot properly monitor the system or command the contactors to close, ensuring a permanent non-start condition even if the primary high voltage fuse is replaced. The required diagnostic steps include checking the module's power and ground, inspecting its connectors and wiring, and running a module self-test if communication is possible.
Do you regularly see cascading low voltage communication codes masking catastrophic high voltage failures in your own bays?
Reference pages for the codes in this article
- P0A95, what we measure for this code across real diagnostics