Volvo s40 1.6 diesel lost power and cut out no warning lights

The usual cause of this is a bad PNP switch or gear position sensor.
The "W" is flashing because the transmission control module is stuck in the Winter mode. If you are not familiar with sensor, I suggest you go and have the transmission codes read and reset to begin with and then post back the results.

Check fuel filters.

Dirty connection on a main fuse or a possibly even a simple thing like a high resistance on a battery terminal caused by corrosion ,the alternator is charging but when the battery connection plays up then the alternator can only produce a certain amount of power ,use a bit more and it stops like you describe ,start by cleaning the battery terminals with a bit of emery paper and greasing them then refitting the terminals

Hi R, As the vehicle started after replacing the oxygen sensor I don't believe the two problems are linked. Have your mechanic carry out a diagnostic scan and we'll go on from there. As a matter of interest, why did you replace the oxygen sensor? Regards John

Try changing the fuel filter. If that does not help, have someone test the injector pump for pressure. Last would be a compression test on the cylinders. Drain oil and replace oil filter very soon.

What has happened is the diesel fuel is a lubricant and gasoline is a solvent. As gasoline is much thinner, it could wash down the cylinders and get into the oil pan thinning the oil and ruining the bearings. This would be the reason to test the pressure in the cylinders to find out if you lost compression with the rings in the cylinders.

Next, the injector pump for the diesel has seals and tolerances for inside components. Again, since gasoline is a solvent and not a lubricant, the internal parts could be worn out by not having diesel fuel to lubricate the injector pump parts.

If someone working at the fuel station made this mistake, all the costs should be paid by the station. This is something which could be taken to court if the station does not pay.

Sounds like your ful pump is on its way out

can be anything,gas pump, crank sensor, if your check engine light is on you need to pull the trouble code or codes the will tell you what is wrong.

According to what you describe, it is possible that the valve cover on the cylinder head and the oil pan are dirty ,It is prudent to uncover and check

Have the fuel injectors cleaned out possibly they have a blockage causing both the lose in power and warning light

it could be your oil pump. they are relatively cheap and fairly easy to replace. replace this first and check again. its a type of engine insurance.