2004 s40 code p0300 need help
 

I need help couple weeks ago my stepson found a 2004 Volvo S40 2.4I and we test drove it and it was fine got go and it had a code of P0300 come on and I've changed the coil packs check the O2 sensors they look good after I reset the code to the first two times then I get a P0 303 and then it went back to a p0300 so I don't know what that is about and I feel bad for him cuz it's his first car any help somebody can give me I would greatly appreciate it me being a Chevy person I'm like stuck

The 5-cylinder engine in that vehicle has been in production since 1992 in various forms. It is a very reliable and easy to service vehicle.

I've seen people plug the coil packs into the wrong harness. You need to make sure that you have each coil plugged in at the plug that is facing the coil. The wiring takes a set over time.

You didn't mention changing the spark plugs. Install a basic set of resistor plugs (nothing fancy) and use a little bit of anti-seize on the threads. Also make sure that the coil packs that you bought don't have a free-floating piece in the center between the coil and spring that touches the plug. I've seen those fall apart and fail.

PM me if you have more issues. BTW I use Denso plugs on these cars.

While the generic misfire codes typically point to spark issues (coil, plug), they can also be caused by fuel trim issues. Do you have any other symptoms other than the check engine code? To note, for my Gen 1 S40, when my fuel pressure regulator started acting up, it had long cold started and would occassionally throw a P030X code - which disappeared once I put the new FPR in. It can't hurt to throw in new plugs (OEM or basic plugs work best) but you may need to also look for vacuum leaks, measure up the fuel pressure for any oddities, inspect the coil packs etc. BTW, I am using basic Autolite plugs on my S40 and on my 850T had good results with Bosch copper cores.

Vilvo ok when I pulled the plugs there denso sk 20hr11 now I've been reading that this car is very sensitive with spark plugs I don't know if those ones work good for it or not they look like they're in really good shape when I pulled him out so I didn't think to change those I pulled the front O2 sensor that look good I cleaned the mass air flow sensor and did a self check on it with voltmeter I'm just trying to figure out what I'm missing and what is doing is is not only has the codes but it's has a real rough idle when you accelerate and stumbles a little

Also I did do a fuel pressure check and it was around 50psi at idle is there a way to check the fuel pressure sensor with a voltmeter

note your model may only have a fuel pressure sensor not a regulator like on the Gen1s...

Also be aware that with the coils sitting over the spark plugs you can get these hairline cracks in the plastic part that sits down on the spark plug. When they develop these tiny cracks the spark can jump to the head and cause a misfire and you cannot see it or hear the pop-pop-pop due to the hidden location. The test is to coat the plastic part in high temp RTV to see if it cures the misfire.

Vacuum leak? There are a lot of hoses (don't forget the one under the throttle body that comes off when you're pulling the plastic intake assembly - easy to miss it).

Still guessing
 

Ok I changed the plugs and cleared the code it ran good for about 15 mins and started rough idle and while using code reader I did Im readiness test andnow I have a code that hasn't triggered all the way yet but it gave me a p0303 so I don't know and I did make sure coils packs were good even though they were new now can anyone tell me during a live data review I noticed the 2nd O2 sensor was jumping around alot is that normal does anyone know what all the numbers should be in live data on everything

FWIW, I'd never change all the coil packs - even if you used new Volvo-blessed packs, the odds of a new one dying are higher than one that's been in there happily sparking away for the last 100,000 miles. This is due to what engineering types call the "bathtub curve" (failure rates start out higher as manufacturing defects take effect, and then the parts get really reliable for a long, long time until they eventually wear out - the other upslope of the "bathtub curve").


That said, the way to make sure it's NOT just a bad (new) coil is to swap out the offending coil for another one. Normally this means swapping the suspect coil with its neighbor, and seeing if the code follows the coil to the coil's new location, or stays in place (absolving the suspect coil of any hint of error).


There could be a problem with one of the injectors, too - it's easy enough for one to get clogged up, and not difficult to do the same technique (swapping a suspect injector with a neighbor) to see if the problem follows.

The O2 readings are a little bit of a mystery - they normally jump around quite a bit, depending on the type. If you can read fuel trim on your scan tool, it might give you a hint as well (won't go into all that yet).

I've tried switching the coils around and it's still saying p0303 and no I just got a generic scanner so it doesn't do fuel trim I'm just new to this whole Volvo thing and I tell you they're different I really like the car my but I'm about at my wits end and later today when I get home I'm switch the injectors and see if that changes anything I do appreciate all your help

It can also be hairline cracks in the spark plug leads on the other two cylinders that don't have a coil.

??? Leads? Cylinders without a coil?

Do what I'm confused

I was just wondering what Hudini was referring to - there are obviously coil packs on all six cylinders, and no spark plug "leads"... maybe he has another old Volvo that he was thinking about when he wrote what he did.

Did you try the injector swap yet?

Yes I swapped the injectors and the coil packs and plugs from 3 to 1 on all three and I'm still getting p0303 now it's only showing up in a pending code does that make a difference and when I first started it and let it run alittle bit it first was a p0300 and then after like 5 mins running it went to p0303 can it be the wiring to the coil packs maybe do u know a way to test them or what the voltages r supposed to be so I can check with a voltmeter meter and I wanna say thank u again for trying to help

A pending code just means that the condition hasn't been seen by the ECM for long enough to light the "check engine" light, but it is coming.

Ok do u know if there's a way to check the wiring to the coil packs or do u have a clue what I can look at next

inspect the connectors to the coils for cracks - you may want to try removing the cover and run the engine in a dark garage (say in the evening) to see if you can see any voltage arcs. Did you also check your plugs for correct fit and gap? If all looks good, I'd probably go back to looking for an intake or vacuum leak (smoke test or spraying around with some carb cleaner may be in order)

Well I can't run it with out the cover since it's the 2.4 the 5 cylinder and the coil packs r under the intake and I'm figuring since it's only the number 3 cylinder showing up misfire and I've switched the three to the one to the 5 and it's still showing only number 3 misfire I'm thinking it's the wiring and Ive checked for vacuum leaks