2004 S40 98K miles with intermittent no start. Dealer could not diagnose or replicate. No codes, alternator good, battery good. When it happens waiting 5 to 10 minutes will usually get it started. When turning key to start when this happens, no noise from starter or its solenoid; simply normal dash lights and the whirring from the electric engine fans under the hood. I was going to have the starter replaced (over $900) but dealer would not guarantee anything since they could not replicate the condition.

Any advise........other than taking it to the junk yard?

 

My 02 S40 had a similar issue. No start, no crank, no click.

It was the neutral starting switch (ie pnp switch) sitting on top of the transmission as the gear change selector. The contacts inside wear and the car doesn't know you are in park so won't start. Try cycling the gears from park to 2nd a number of times then back to park and try starting.

Switch is a 20 min replacement job, about $100 from Rockwauto.
AIRTEX / WELLS 1S6932 {#30896813, RB4011} Neutral Safety Switch

 

a few thoughts - could be the starter, the cable to the starter, the ignition switch or the immobilizer (not sure if your model has the battery in the immobilizer) or the PNP switch.

So starting with the easy, next time it won't start, try the ol' shifter row. If that doesn't work, try wiggling the key when trying to start. Next try locking/unlocking the doors 5 times with the key fob (this is supposed to reset the immobilizer). When you try to start and fail, see if you can see the headlights dim (ie that says power is getting to the starter). If nothing yet, its time to check the battery cable to the starter - clean surfaces, look for cracks in insulation etc. Doesn't seem like a typical starter problem to me. Usually the symptom is a solenoid click but no spin. I'd also do some research on the immobilizer system - on some Volvo models there's a rechargeable battery to power the security alarm even if the main battery is dead. If that battery dies, then it can set the immobilizer off. Not sure if the 04 S40s share this design.

 

Thanks. To reset the immobilizer, locking/unlocking the doors 5 times, do I HAVE to use the key fob? Can the same be accomplished using the power door lock button on the front doors? Does it matter if we are using the valet key exclusively?

 

If there is an issue with immo you would see message on the dash.
So look at the hood where distribution box is located.
Get ear closely and have someone engage ignition.
If you can hear small relay clicks that means you have starter issue or faulty this small relay or power to the starter is intermittent.
If relay is good (you can swap with some other relay) don't hear clicks that mean it can be neutral issue as somebody else said.

 

Just an update....replaced PnP Switch (neutral safety switch) on gear selector. Seems to have solved the issue....for now, at least!

Thanks to all that responded!

 

Thanks for sharing the outcome. Good to know!