Even the best families sometimes have to face a dead battery and the likelihood gets stronger with every new model that appears on the market. Electricity is taking over. Power steering, handbrakes and rear-view cameras are the latest fittings that require a flow of electrons to start functioning.
In the old days, this was not a problem. Gather some family or friends, even bystanders, and ask them to push while you select second gear, switch the ignition on and release the clutch as soon as the speed was high enough. Alternatively, you could commandeer another motorist to help you with a jumpstart.
Coping with a dead battery has now become a more serious matter. Push-starting cannot be done with an automatic transmission. The torque converter will not transmit enough movement to the engine to get it to rotate fast enough to start. It is also not recommend for a manual-gearbox car with a catalytic converter. Unburned fuel may enter the converter in sufficient quantities to cause damage. Jump-starting carries a high risk for the computers onboard a modern car. The Robert Bosch company advises that this should be done only in a dire emergency.
The following occurrence illustrates the way some manufacturers protect their vehicles against such risks. David Nathaniel Adams, known far and wide as DNA, did the only thing he could possibly do with initials like that. He became a biology teacher.
We normally service his W123 Mercedes-Benz 230 and he recently brought it in. The car suddenly became difficult to start, did not like to idle when cold and idled fast when at normal temperature.
Hennie, who owns a similar model, poked around under the bonnet but could not find anything wrong without a step-by-step examination of the fuel injection system. He therefore asked me to get more information from DNA about the events leading up to the problem. I phoned the latter and he admitted that he had forgot to tell me that somebody in his family left the lights on in his car and he had to organise a jumpstart. The trouble began after that event.
This news cheered Hennie up because it solved the mystery. Mercedes-Benz fits an over-voltage protection relay to safeguard against voltage spikes during a jumpstart. On this model, it’s mounted at the back of a plastic cover behind the battery. Hennie went to the relay, saw the fuse was blown and fitted another one. The engine started easily and subsequent road testing showed that the fault was gone.
I explained to DNA that this relay controls the idle circuits. When it’s not working, the car won’t idle, will be difficult to start and run poorly.
I then explained the safe way to jumpstart a vehicle, which is as follows:
1. Connect the red positive cable to the positive terminals on both batteries;
2. Connect one end of the black negative cable to the negative terminal of the donor battery, and the other end to a metal part on the dead engine as far away as possible from the dead battery to prevent a spark from occurring near the battery;
3. Wait three minutes for the battery voltages to stabilise;
4. Start the donor engine and let it run for a minute;
5. Start the dead engine and let it run for a few minutes;
6. Switch off both engines and remove the cables in reverse order.
