Car starting problems: we often think of a dead battery, a faulty alternator, or a worn-out starter. But sometimes, the causes are much more obscure and technical, related to unexpected electronic or mechanical failures. It is essential to understand these car starting problems to avoid costly repairs.
A concrete case: the Audi A5 that refused to restart
Our workshop encountered an intriguing case: an immobilized Audi A5, displaying multiple error codes, including one related to the high-pressure injection pump and another to the crankshaft timing. Despite replacing these parts, the vehicle remained silent.
The real culprit? A short-circuited water pump sensor. On this engine, the crankshaft sensor, the camshaft sensor, and others operate with the same 5-volt reference. By disconnecting the water pump, which was starting to leak, the engine restarted instantly. Replacing it permanently solved the problem, a case so rare that our manager had never seen one in 20 years of his career.
Faulty sensors: the invisible culprits
Crankshaft and camshaft sensors are the most common causes of a no-start condition. The engine control unit uses them to synchronize ignition and injection. If it receives incorrect or missing information, it can block the starting process to prevent engine damage.
Problems with the tone ring
The tone ring is a toothed wheel read by sensors to determine the position and rotational speed. If it is misaligned, damaged, or if the tooth sequence is incorrect – for example, after an engine replacement – the data becomes inconsistent. The control unit, “confused,” then refuses to start.
Chewed cables: an unexpected scourge
Rodents appreciate the rubber insulation of electrical wiring harnesses. A car parked for a few days is enough for them to settle in the engine compartment, attracted by the heat, and gnaw on the cables. Several times a year, we discover nests responsible for phantom breakdowns, with no error codes, resolved simply by repairing the damaged cable.
How to diagnose a complex breakdown?
When faced with a no-start condition, start with the basics: test the battery and listen for a click when turning the key. If the problem persists, an electrical diagnosis and a scan with a professional tool are essential to read the error codes and trace the faulty circuit, especially in the absence of an obvious cause. In summary, car starting problems can be multiple and varied.