Will not start

Hello,

It sounds like the crankshaft angle sensor has gone bad and the computer is not turning the fuel pump on becasue it does not see the engine turning over.

Here is a guide that will show you what you are in for when doing the job:

https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

and

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

and

https://www.2carpros.com/articles/car-cranks-but-wont-start

Here are some diagrams to show you how it is done on your car.

At left front of transmission housing.

Please let us know what happens.

Cheers, Ken

Is it cranking over and will not start or just will not crank over at all/nothing when key at starting position?

You are describing the classic symptom of a failing crankshaft position sensor or camshaft position sensor. They commonly fail by becoming heat-sensitive, then they will work again after cooling down for about an hour. While driving, natural air flow keeps them cool. When a hot engine is stopped, the heat migrates up to those sensors and can cause them to fail until they cool down. This can happen on any brand of engine and is easily overlooked at a used-car dealership because they do not drive the cars long enough for the problem to become apparent.

There will usually be a diagnostic fault code set to indicate when a sensor circuit's signal is missing. The place to start is by having the fault codes read and recorded. The people at many auto parts stores will read them for you for free.

Sorry, I would like to, but there are way too many variables. The additional point of value is diagnostic fault codes never say to replace parts or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is actually the cause of that code about half of the time. First we rule out wiring and connector terminal problems associated with the sensor or part, before we order the part. Electrical parts can rarely be returned because so many are damaged upon incorrect installation, and the parts store does not want to risk selling you a defective part that someone else returned. For that reason, the mechanic has to be pretty sure that part is really needed.

The next problem is some sensors are really easy to replace. Many can be replaced on Chrysler and Ford products in two or three minutes. On some engines a lot of disassembly is required, and they can take well over an hour. Add the additional time to get to a sensor to take some voltage readings, and you might add another hour diagnostic time to the part replacement time. I am not familiar with Audi engines but I did find your crankshaft position sensor is listed in the "flat rate" guide as taking 1.1 hours for just the replacement. That tells me it is a pretty involved job.

Remember, nothing has been diagnosed yet either. There are a number of computers and electronic modules that can cause a crank/no-start. I only jumped on the sensors because the failure only when hot is such a common symptom with them. No conscientious mechanic would waste an hour of your dollars based solely on the symptoms. If he is wrong, how are you going to feel when he tells you your money was wasted on his guess? Worse yet, how is he going to feel when you call the shop and tell him the problem occurred again when you are twenty miles from the shop?

Hi HUGODB,

While you are waiting for one our experts to answer your question here is a link to an informative article from this site with step by step instructions and pictures and a video on what to check for when your vehicle cranks, but will not start.

https://www.2carpros.com/articles/car-cranks-but-wont-start

If you need any further help please come back to the site as we are always happy to help.

Thank you for visiting 2CarPros.

Kindest regards,

Renee
Admin

Maybe starter drive has failed (slipping).

Starter fault. The whine is motor turning but pinion gear not engaging flywheel.

Go to Auto Zone have alternator checked then you will know. Also if alternator good may have drain caused by a circuit staying on when key off. Like trunk light, glove box etc.

Fuel and Spark:
Get a helper disconnect a spark plug wire or two and ground it to the engine at least 3/16 away from ground -have helper crank engine over do you have a snapping blue spark? If so you have a fuel related problem, check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs, coil's resistances, distributor pick-up coil, ignition control module, cam and crank sensors and computer.

First check fuel pressure with mechanical gauge. Some engines have a "cold start valve" which only works when cranking adding addition gas to engine when cold.

Newer engines simply increase injector pulse time, which is controlled by PCM.

But, I would start with fuel pressure check.