Why Land Rovers Are Prone to This
A modern Land Rover or Range Rover communicates via a CAN bus network that connects 40+ individual ECUs. When you turn the key off, these modules are supposed to complete their shutdown sequences and go to sleep, leaving only the bare minimum (clock, alarm, remote entry) drawing power. The problem is that JLR's CAN bus architecture means that one module that doesn't sleep properly can keep others awake — because they're waiting for it to complete its communication handshake. The result is a chain of modules drawing current that should be at zero. Normal quiescent current (resting draw) on a Land Rover after full sleep should be under 50mA. A vehicle with a parasitic draw problem may be drawing 500mA–2A continuously, which depletes even a healthy battery within 48–72 hours.
Most Common Culprits by Model
L322 Range Rover
LR4 / Discovery 4
Discovery 5 / L462
The Discovery 5 runs an even more complex electrical architecture. Battery drain issues on these vehicles are typically traced to the TCU (telematics control unit), the InControl Touch Pro infotainment module, or the body control module. The key difference with newer platforms is that the modules communicate over a more complex network topology — isolating the offending module requires reading the CAN bus traffic during the sleep sequence, not just current-clamping individual circuits. This is a task that genuinely requires JLR SDD and a trained technician who knows what the sleep sequence should look like.
The Right Diagnostic Approach
Proper parasitic draw diagnosis follows a specific sequence. First, a current clamp is placed on the negative battery cable to measure total quiescent current after the vehicle completes its full sleep cycle (typically 20–30 minutes after door closing on Land Rovers). If total draw is above 50mA, individual fuse circuits are isolated one at a time — by pulling fuses — to identify which circuit is the source. Once the circuit is identified, the specific module on that circuit is isolated. The process takes 45–90 minutes minimum and cannot be rushed. A technician who does the test over 5 minutes is not doing it correctly — the vehicle needs time to cycle through its sleep sequence between fuse pulls or you get misleading readings.
What Doesn't Work
A battery voltage test tells you the battery is dead or weak — not what killed it. A battery replacement without finding the parasitic draw source just means you'll be calling for a jump in two weeks with a new battery. Fault code reads don't reliably identify sleep-mode failures because the module that's draining the battery often logs no fault codes. You need a current clamp, a fuse chart, and time. Our trained technicians have the process down to a reliable sequence that typically identifies the culprit on the first appointment.