Humming is the vacuum pump. If you push the brakes it should kick on too.

 

So I'm new to these cars, so my advice is more "conventional wisdom" than Volvo S40 specific.

What you are describing sounds like something wrong with the starter or the starter solenoid. Typically if it is a bad starter when you try to start you can hear a clicking noise from the solenoid. Sometimes it is just the one click, sometimes it will be rapid clicks (rapid clicks normally mean the battery is too weak to crank the engine). If you hear a single click then you can be assured the car is trying to start, the solenoid is working, and the starter is probably shot or shorting out somewhere.

If it you can't hear a click it either means the solenoid is bad or perhaps the car has sensed something wrong and won't try to start the car. Again, I don't know enough about these cars to tell you if that is a possibility or not, I'm more familiar with "dumb" cars. I also don't know if the click of the solenoid can be heard on these cars, but every other car I've worked on it is pretty easy to hear when the car won't crank.

 

Is it possible to pull the endcap off ours and push the starter in with a screwdriver? I've had to do that before and even put a button on my harley so I don't have to waste the amperage on the solenoid doing it's job. High voltage and amperage though, so don't kill yourself. See if it will turn over or if the solenoid isn't pushing it far enough in. Some people smack their hammer with a starter to see if it's bad and then try to start it again, if it works you know it was bad.

I personally bought an upgraded 0000 or 4/0 AWG gauge cable premade with silicone insulation that now sits between the starter and the battery for like $25 off ebay. The OEM one is like 1 or 0 AWG, can't remember, not great for passing through so many amps (150% on start and then 100% at about what 1.6 or 1.8kW). starter performance increased immensly.

In terms of starting the car, I know the ring sensor in the key slot can go bad, starter can go bad, and a few other things, but start simple and work your way out from there.

 

I bit the bullet and took the starter out. The short cable between the solenoid and the starter motor corroded away so there was no connection. It looks like the power is routed through the solenoid to the starter motor so I don't think the motor was turning when I tried to start the car. I'm not sure about the sounds I was hearing when I tried to start it - there was a humming that I believe is a vacuum pump as Jirv0id mentioned but there was also a whirring that sounded like it was coming from the passenger side of the engine. At any rate, I'm debating whether I should get a rebuilt starter or find a suitable cable to connect the solenoid to the starter and try to solder it to the nub that remains on the motor. The car has 217k miles so maybe it's time to replace the starter?

 

I know I am resurrecting an old thread but It was helpful in diagnosing my No Crank / No Start problem. My V50 T5 M66 suddenly wouldn't crank. VIDA/DICE showed no codes and there were no other symptoms. When I turned the key to III there was just a single click of a relay. I checked and charged the battery. Initially I thought it might be related to the clutch switch since I had the clutch master cylinder replaced and was having issues with a leaky line. That checked out OK. I disconnected the battery and reseated all the CEM and ECU connectors and tried again but still no joy.

After reading this thread ... could it simply be the starter? I checked battery voltages at the starter. Then I checked the voltage of the solenoid control wire while I durned the key. The voltage went to 12V when the key was in position III. Bingo! The starter was the fault with out prior warning. I then did the old mechanic's trick of tapping the solenoid with a hammer, turned the key... it cranked and started.

Now I am waiting for my replacement starter to arrive from FCP Euro. It seems that these starters are getting harder to find.

 

It must be P1 starter season. My starter died last week while I was on a road trip three hundred miles from home. Had to have it towed; thankfully, there was a Volvo specialist five miles away from where it broke.

 

I got my replacement starter today and installed it. All is good. I had to laugh at the sticker on the new starter since that is how I got the old one to work.

 

I replaced my starter 2008 s40 correctly and when I went into the car to start the car electric smoke started coming from the starter. Help what is the issue