Undervoltage has been detected in the vehicle. This means the same as a flat battery. A flat battery can be caused by the customer or by a defect on the vehicle. The entry 'Undervoltage' does lead to the conclusion that there is a defect in the control unit itself.
The possible cause determined is that the sidelights or hazard warning lights were switched on for too long with the vehicle parked.
The possible cause determined is that terminal R or terminal 15 were switched on for too long with the engine off. The current consumption of the vehicle is then, depending on the equipment, 10-15 A. This discharges the battery very quickly. If possible, point out these facts to the customer.
The possible cause determined is that the vehicle was parked for a very long period. The vehicle has a standby current consumption of 20-80 mA, depending on the equipment. This leads to slow but continuous battery discharge. Depending on the state of charge of the battery when the vehicle is parked, the residual capacity necessary to start the vehicle is reached after an immobilisation period of approx. 4 - 12 weeks. If possible, point out these facts to the customer.
The possible cause determined is that the battery has been discharged due to unfavourable driving characteristics on the part of the customer. Unfavourable driving profiles can be:
- Short distance driving less than 8 km: In the case of extreme short-distance driving, it is possible that starting the engine takes more energy from the battery that is charged in the subsequent trip.
- Very few trips: If the vehicle is moved very infrequently and the individual trips are not sufficiently long, it is possible that during the immobilisation period more energy is taken from the battery by closed-circuit current than is charged while the vehicle is being driven.
If possible, point out these facts to the customer.
If there is a suspicion that the battery is defective, the battery must be checked using the battery tester.
The result ”Excessive closed-circuit current” means that the vehicle, occasionally at least, has had a closed-circuit current greater than 80 mA. Here, the vehicle was in the idle state, that is, the bus systems were inactive. A possible cause of this could be defective control units. For troubleshooting, run a standby current measurement.
If the vehicle does not reach the idle status (sleep), that is, the bus systems remain active, the control unit causing the fault is generally determined by the energy diagnosis. Troubleshooting must then be continued in the peripherals of each control unit. If no fault is determined, the control unit must be replaced.
If the vehicle keeps being woken up, the bus system causing the waking is determined by the energy diagnosis. In addition, it is determined whether the recurring wake operations occur with terminal 30g on or off. If the wake operations have taken place with terminal 30g switched off, the control units connected to terminal 30g can be excluded as possible causes.
Note: In exceptional cases, it is possible that the result ”Vehicle keeps being woken up” is generated by unfavourable customer behaviour. (E.g. frequently waking of the vehicle at terminal 0 by opening and closing the luggage compartment lid or doors.)