This LRO reader emailed LRO.email@example.com seeking help for his P38 Range Rover and its ECU sleeping issue.
The battery on my P38 Range Rover 4.6 HSE goes flat after just three days if the vehicle isn’t driven. The battery and alternator have both been replaced and the ECU has been serviced. A full diagnostic check showed no problems. This is a long-standing problem, so I’d be grateful for any suggestions.
Dennis Room, Birmingham
Your problem could be related to your ECU not sleeping properly. The ECU draws about five amps when active but, after the vehicle is locked, it sleeps and current consumption drops to about a tenth of an amp. Unfortunately, spurious signals picked up by the door remote control receiver can re-active the ECU, increasing load on the battery and giving the symptoms you have.
To check, remove the earth lead and put in an ammeter (set to the 0-10 amp range) between the lead and the terminal. Wait for the ECU to go to sleep and then keep an eye on it to see if it re-activates. There is a cure: replacement units can be found on a different frequency that aren't prone to this problem.
This workshop advice appeared in the October 2007 issue of LRO. Back issues are available to download on digital devices here.