Learn a few simple tips and mechanic terminology that may help when you are stranded to get back on the road faster.

While German cars are renowned for being well engineered and reliable, they are certainly not exempt from faults. Having your car not start is one of the most painful experiences a driver may face, either leaving you stranded somewhere or making you late while you arrange another means of getting around.

While there are many obscure causes for a car not starting, 90% of occurrences are attributed to only a handful of issues. Before we look at some of the causes, we first need to identify if the engine ‘cranks’ or ‘does not crank’.

What is cranking?

Crank, cranking or turning over

Cshaft_18_frameAnimation showing piston and crankshaft motion in an internal combustion engine such as an automobile engine.

Source: https://en.wikipedia.org/wiki/Crank_(mechanism)

, refers to the engine rotating. If an attempt to start the car is made and the engine does not start, the first piece of information a roadside technician will want to know is whether or not the engine is rotating. If you turn the key to attempt a start and hear a repetitive noise from the engine, this is one indication that the engine is cranking. If no repetitive noise is heard or there is just a few clicking noises, the engine is not cranking.

The clicking noise heard is in most cases the sound of the
starter motor
Starter Motor
The starter motor is a powerful electric motor that provides the initial impulse to turn over the engine to start it. It requires a very high current to crank the engine, which is why it is attached to the battery with large cables.
attempting to start the engine.

Now we have identified the difference between cranking and not cranking, let’s look at the common issues.

Engine does not crank

Battery related issue

How to identify

  • Absence of dash warning lights such as battery light and engine light
  • Headlights or other electrics in vehicle not operating or dim
  • Last few start attempts have been slow cranking

The most common cause of the car that won’t start is of course the battery. It takes a huge amount of battery power to start the engine far more than any other electrical item. If a battery has gone completely flat the engine will not even attempt to crank, and none of the vehicle electrics will work. If the battery is only partially flat, electrical items of the car may still work, and the starter will attempt and you may hear a clicking noise.

How to fix it

If you know where your battery is located, checking to see if the battery terminals are tight is a good place to start. Many cars have the battery located in a spot that is not easily accessible such as under the seat or behind coverings or ducts. A roadside assistant mechanic may be able to perform a jump start or replace the battery on the spot.

After the repair

An important question at this point would be to ask why the battery went flat in the first place! If it is more than three years old it may just be due to age, or perhaps there was something left on in the car causing the battery to drain. Your local specialist workshop like Ammstar Autohaus will be able to check the vehicle’s electrical system to ensure the battery charges at the correct rate, and there isn’t something secretly staying on in the background causing the battery to drain.

Starter motor failure

How to identify

  • Electrical items in car working
  • Last few starts may not have worked on first few attempts
  • No click heard when start attempt made

The starter motor is an electric motor that gets the engine cranking. Sometimes a starter motor will fail and give no warning or indication at all. Starter motors have an engaging gear that is operated by an electrical solenoid. On older model cars a roadside mechanic’s could often give the starter a gentle tap with a hammer to make the starter operate! While this trick can still work on modern German vehicles, the starter motor isn’t always that accessible, this is the case on many BMW engines where the starter is located under the intake manifold!

How to fix it

If the ‘tap with a hammer’, or other tricks attempted by your roadside mechanic’s didn’t get the car started it is unfortunately time for a tow. Most starter motors are readily available and you can be back up and on the road within a day or two. It is always good policy to replace the starter motor relay, a specialist repairer would advise you of this.

Immobiliser / key failure

How to identify

  • Start error / immobilizer fault warning on dashboard
  • No response from ignition
  • Headlights or some electronics may still work

To prevent vehicle theft, vehicle makers now have very elaborate systems to ensure only the correct key can start the car. The Mercedes-Benz system for vehicle drive authorisation uses not only an immobiliser, but integrates several electronic control units such as the ignition switch, steering lock, engine and transmission control units. A common issue with the C Class Mercedes-Benz between 2007 and 2012 is the steering lock failure, which prevents the car from being enabled.

How to fix it

Try your spare key if you have one. If you know your key has been water affected (like you had it in your pocket when you went surfing or dropped it in the sink washing dishes…) then your key has no doubt failed. You may be able to order one directly from the vehicle dealership with some security documentation to prove you are the owner of the vehicle.

If it is not just the key, unfortunately there is no much that can be done on the side of the road. Only specialist repairers car fix or replace components in these complex systems.

Engine cranks, (and cranks and cranks and cranks)

Fuel pump

Most modern petrol (gasoline) powered vehicles have a fuel pump located inside the fuel tank itself. If you have ever heard a ‘buzz’ from the rear of the vehicle when you first turn your ignition on, that is the sound of the fuel system being pressurised by the fuel pump.

What to check

It may seem obvious, but the car may be out of fuel. Fuel gauges can be less accurate when reading below one quarter of a tank, so have a think about how many kms you have travelled since you last filled up.

If you are quite certain the fuel level is ok, it is likely the fuel pump has failed. Your roadside mechanic may again use his skills to give a ‘gentle tap’ to the fuel tank to jolt the fuel pump, the car may even start after this! While it may be ok to drive away, the likelihood of the failure occurring again is high. Most fuel pumps are readily available, and are replaced as part of a fuel delivery system which incorporates the in tank level sensor or ‘sender unit’. Your specialist should be able to provide you with a full accurate quote on the cost of this repair.

Crank position sensor

crank sensor
Crank Sensor
An electronic device used in an internal combustion engine, to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control the fuel injection or the ignition system timing and other engine parameters.

detects the speed at which the engine rotates. Electronic fuel injection systems rely on this sensor for just about everything. With no crank speed signal, the engine will not start.

How to identify

  • Hot summer day
  • Will not start after having driven some distance
  • Starts again when left to cool down

Crank sensors have been failing for as long as electronic fuel injection systems have been in production! These sensors sensitive to temperature, and the vehicle will often start again once it has had time to cool down.

Diagnosing this fault and replacing the sensor is a relatively simple job for a skilled technician, which means your car won’t be off the road for long at all. Rather than taking the risk and breaking down again, it is safer to arrange a tow.

The other 10%

There are many other edge cases that can cause your car to not start, from random electrical wiring issues to a seized engine. A skilled technician or brand specialist will work through a systematic process to identify faults. The hardest faults to diagnose are ones that are intermittent and occur infrequently. To help in diagnosis of this fault, take note of as much information as possible, how long the car had been operational, ambient temperature and if there is anything else that happened at the same time. It may just help your repaired get your car on the road faster for less!

Experienced a start issue on you BMW, Audi, Volkswagen or Mercedes-Benz? Ammstar Autohaus are brand specialists, and offer a true dealer alternative in Melbourne. Call today on 9585 1676.