CAR CLINIC | Making sense of car electrical problems

Mechanical problems are in general relatively easy to pinpoint, but it may take days to do the repairs.

With electrical problems the situation is often reversed: they might take days to diagnose accurately, but once they have been identified, repairs (or, more often, replacements) can usually be done within hours. 

In a conversation I had with an experienced auto-electrician, he raised the interesting point that the electrics on modern cars are on the whole very reliable, certainly more so than on cars of 40 years ago when a certain manufacturer of generators and headlights earned itself the title of “Prince of Darkness” because its products were notorious for leaving you without lights at night.

Today's alternators will routinely last 200,000km with nary a hiccup.

But there is a flipside to this coin. Modern electrical systems, incorporating sensors, microprocessors and electronic control units, are vastly more complex than those of the past. Amateurs should never be allowed to tamper with them, no matter how clued-up they may purport to be. Home mechanics, in particular, should leave the electrical system on a modern vehicle alone, painful as it is for an ardent proponent of DIY maintenance like me to say so. On older cars it is a completely different story, fortunately!

The auto-electrician I spoke to said the majority of problems ending up in his workshop originated with unqualified technicians attempting auto-electrical work on late-model cars.

As typical examples he mentioned taking power for aftermarket spotlights from unsuitable points on ill-chosen circuits, or pinching wires when installing bull bars. Jump starts, both giving and receiving, is another thing that is best avoided altogether on modern cars.

I would prefer to take any electrical problem on a modern car directly to a reputable, qualified auto-electrician, rather than leave it to a general workshop for them to decide whether to call in an auto-electrician.

The owner of an independent car workshop to whom I chatted recently regarded hard starting from cold, and a failing starter battery as two of the most common problems encountered at the onset of winter. The two things may, or may not be linked. Lead-acid batteries which are still the type of starter battery found in the great majority of internal combustion engines, are known to have less “staying power” at lower temperatures.

The amp-hour capacity at 0°C may be 20% lower than at 25°C. Thus a battery which is on its last legs may still soldier on in hot weather, but will most likely fail when the first icy mornings arrive. For this reason the workshop owner recommended that if your starter battery is more than four years old, you should have a load test done on it in autumn to determine its state of health. At the same time the performance of the alternator should be checked.

Ongoing research & development is taking place in the field of starter batteries. Improved wet-cell batteries, gel batteries, absorbent glass mat (AGM) batteries, lithium ion batteries, and sodium ion batteries are all being developed. Some cars are notoriously fussy when it comes to replacement batteries — the new battery has to conform very closely to the factory-fitted one, otherwise mysterious warning lights begin to flash on the dashboard. Again, a consultation with an auto-electrician will be a good idea.

The hard-starting-from-cold syndrome, now far less common than in the days of carburettors and chokes, presents a conundrum of its own. It is always a highly irritating experience, and it's tempting to blame the battery immediately, especially if the poor thing is long in the tooth.

But hard starting can have a host of other causes: loose or corroded connections somewhere in the starting circuit, a defective starter solenoid, wear in the starter motor, defective glow plugs (on diesels still using glow plugs), worn fuel injectors, problems in the fuel pump circuit, loss of compression, a clogged air filter, malfunctioning temperature sensors preventing fuel enrichment, a bad idle air control valve, worn spark plugs or failing plug wires, a bad crankshaft position sensor ... to name just a few.

If the starter cranks the engine enthusiastically (at least initially — it will inevitably grow tired) but the engine refuses to start, the problem is unlikely to be in the battery or the starter circuit.

Most of these gremlins, whether in the battery, the starter circuit, or elsewhere, will give you some prior warning before leaving you stranded. The signs may be subtle and intermittent at first, but if you are attuned to your car, you will pick them up. Have them traced as soon as possible. They will not go away by themselves. The world's first self-curing car is yet to be produced.

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