Our Diagnostic Process
When a Land Rover arrives with a battery drain complaint, we start with a JLR SDD scan for stored fault codes — some draw issues log as module communication faults before they fully manifest. We also review the battery management system's charge history if the vehicle has one (available on L405, L462, and late L494 models). Then we begin the actual parasitic draw test. A current clamp is placed around the negative battery cable, measuring total quiescent current flow from the vehicle. We wait 20–30 minutes for the vehicle to complete its full CAN bus sleep cycle — Land Rovers take longer than most vehicles because of the number of modules involved. Once the vehicle is fully asleep, we record total draw. Normal quiescent current should be under 50mA. If it's higher, we begin isolation.
Fuse Isolation
Isolation involves pulling individual fuses one at a time while watching the current clamp reading. When a fuse pull drops the draw significantly, we've identified the circuit. We then use the wiring schematic and JLR SDD module map to identify which ECU or component is on that circuit and why it might be staying active. Common culprits on Land Rovers include the EAS ECU (L322), the infotainment module (LR4 2012+, Discovery 5), the telematics control unit, and the transfer case module (L322, LR3). Between each fuse pull, we wait for the vehicle to complete a partial sleep cycle reset — this can't be rushed or the readings are misleading.
After We Find It
Battery Replacement
Battery Registration (L405, L462, L494)
Late-model Land Rovers with a Battery Management System require battery registration after replacement — a procedure performed with JLR SDD that tells the BMS the new battery's specifications and resets its charge algorithm. Skipping battery registration on an L405 or L462 results in the BMS using incorrect charge parameters, which either shortens the new battery's life or triggers false low-charge warnings. We include battery registration with every battery replacement on applicable models. There's no extra charge for this step.