I'm not sure which years of XC90's or models of volvo's that have this issue but there seems to be a lot from what I have read. The symptom is the car will turn over but doesn't want to start. You will get various trouble codes and warnings on the dash. It will eventually start and seams to be worst in hot weather or when the car is hot. Once it starts it runs as if nothing is wrong until it is time to start it again.

I have a 2004 XC90 T6 that has done this for 3 years. The dealership could not figure out what the issue was so after reading all the post here and all over the web for 3 year, replacing Crankshaft sensors, starts, camshaft sensors, battery, checking all grounds to the engine and coils, with only changing out the starter that helped a little, I finally figured out what was causing the problem. It's not the grounding between the transmission and the engine as there are two grounds, one on the front of the transmission and one on the back of the engine. it's not the flywheel pickup either.

The cause is the Power cable that runs from the jumper terminal under the hood to the starter. This cable runs directly over the crankshaft sensor (4-5 inches above) and next to the camshaft sensor. As your starter gets older and / or the temp of engine or outsides is hot, the starter motor will pull more current & AMP's to turn over the car. This additional current causes a larger magnetic field that interferes with the signal from one or both sensors. (Crankshaft and Camshaft sensors) (I think the Crankshaft sensor is affected most). Which in turn confuses the ECM and the car will backfire or not even try to start. The car will turn over but won't get the signal to fire the plugs at the right time or not at all. Eventually, the ECM will get a correct signal and fire, but this might be after 3 to 20 plus start attempts or not even start at all. The reason a new starter helped was a new motor will draw less current therefore not create a large magnetic field.

The fix is simple: Disconnect this power line at the jumper terminal (under the hood) and at the starter and replace it with a new line that runs around the air filter box away from the sensors. The car will start every time.

Parts needed:
6 feet #2 starter cable
(2) copper #2 terminal leads

Process:
1. disconnect positive terminal from battery
2. under the hood, open jumper terminal compartment and remove the cable from the terminal block that goes to the starter. (on my XC90 it was the one that went towards the passenger side)
3. remove the power lines to the starter. There are two lines. One goes to that Terminal you just disconnected and the other to the alternator. ( if you take off the air intake on the front (2 #10mm socket bolts) and remove it this makes it easy)
4. test out which line run to the terminal and move it out of the way. Mark the alternator line as this will go back on the starter terminal.
5. Place the new cable on the starter connection. (I put a 90 Deg bend in mine about 2 inches past the connector to make it easy).
6. Put the Alternator cable on the starter and bolt both the new cable and alternator cable to the starter.
7. Rout the new cable around the air filter box and back to the jump start terminal. Bolt it back in.
8. Reconnect positive battery terminal
9. Start the car.

I hope this helps all of you that have had this issue and have scratched your head. Someone tell Volvo that running a high current / AMP line near a signal type sensor is not a good idea. Don't let Volvo charge you $$$$ to trouble shoot or replace sensors or starters or a battery. This fix cost less than $25.

Good luck

JB

 

That is very interesting.

 

Yep, and hope that if you get in a collision and that heavy gauge hot wire gets shorted to ground, there isn't any fuel to cause an instant fire. The cable is routed where it is for a reason.

 

ES6T,
The same can be said for where it is routed by the factory. It runs Straight across the front of the engine so a head on collision could cause a ground short. But if I didn't re-rout it, you are right, I wouldn't have to worry about a fire because the car would never start! I guess it could be a nice piece of yard art. Lol but I prefer to get use out of the car.

 

The difference is it has to be routed across the starter, for obvious reasons. It does not have to be routed along the fender.

You could also just replace the starter, since that is the root cause and will likely be failing soon anyway. I prefer to fix things the right way.

 

I have replaced the starter (4 times) with a factory Bosch both new and referbished. It only masks the issue for a short period of time or not at all. So I will stick with a true fix vs a screwed up factory design.

 

You are a damn life saver!!
2 starters 3 crank sensors new sensor connector new sensor bracket i was pulling my hair out.
Car runs amazing and starts like a 400k diesel..

 

This is the most foolish thing ive heard..
theres a reason volvo changed it as well although they'll never admit it.
my p80 is routed entirely different and never had this issue.
must only be trunk mounted batteries that used this cable routing.
Some jeeps had similar issue where ppl removed starter power from harness as it reeked havoc on sensors.
Ive been pulling my hair out for a month trying everything under the sun.
i knew it was an interference issue just wasnt sure if was from wiring or starter itself no way to attach the starter differently lol.

 

I just have this issue. Will try your fix. Thank you so much for sharing.