This is what happened, My wife was out in the car and parked it to do some stuff. When she went to leave it wouldn't start so she called me and by the time I got there the battery was low from trying to start it. I jumped the car and it started right up but the check engine light was on. I checked the OBDII reading and got PO120 (throttle pedal position sensor A). I reset and all was good. I then wanted to test the battery voltage so I shut off the car and got my VOM meter and went to start the car but it won't start.
Anyone have any ideas of what is happening?

 

Oh, I forgot to ask, where is the throttle position sensor located?

 

I owned a 850 for many years and had the same problem, you should check for fuel pressure when it won't start, easily done on the fuel rail however if its ramdom my best bet is that the fuel pressure relay is bad (sometimes works sometimes doesn't) that controls the fuel pump and its usually when you try to restart it again, its very easy to replace just remove the relay cover on the drivers side next to firewall and replace the #103 red relay, cost is about $50 from dealer and $30 online reccommed that you get a new one because used is questionable due the the high failure rate, its a good bet thats it and well worth $50 and 10 minutes work. Good Luck...

 

The thing is that the main and fuel pump relays were just replace a few weeks ago. I let the car sit for about an hour and it started and pulled the same code so am I right in thinking the throttle position sensor is bad?

 

The code that I got on this says "throttle pedal position sensor", is that the sensor by the end of the throttle cable in the engine compartment or is there a second sensor by the pedal it self?

 

I believe that's the sensor at the bottom side of the throttle body. It has a wire plug harness going to it. Unplug it and plug it back in. Also, if you move the throttle at the throttle body you should hear that sensor "click" as soon as you come off of the full closed throttle position.

Hope this helps.

 

How can I tell if it is this sensor or if it is the fuel pump? I have heard that if the car runs fine for a while and then you shut it off and it won't restart that that points to the fuel pump. It was in the shop because it wouldn't start and they jumped out the fuel pump and it work fine at that time but it wasn't getting power so they put in the main and fuel pump relays and then it was fine for about a week, until yesterday.

 

https://volvoforums.com/forum/volvo-...p-relay-64044/

 

Embarrassing moment of the day. Just after I asked I looked at the top of the page and saw that.

 

When I do this do I need the ignition on or will it still click when it is off?

 

Ok I tried this with nothing turned on, with the ignition on but the engine not running and with the engine running and could never hear anything click under any of these conditions.

 

In the picture it's the black box on the right side of the throttle body.

 

I took the sensor off and putting it back on was a real pain. The lower screw was almost imposable to get started, big hands.
I replaced the fuel pump but I can not find any reference in anything that shows which wire is + and which is -. I am guessing that they would not make the red wire a ground.