I have a 2008 Volvo S80. Check engine light came on recently.

Plugged in my OBD II scanner...and got the following codes:

P0303
P0306

When I looked up the definition for these codes...it says the following:

* Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable)
* Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure
* Improperly functioning EGR system, Defective Mass Air Flow Sensor
* Defective Crankshaft and/or Camshaft Sensor, Defective Throttle Position Sensor
* Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems)

Obviously this is a "basket full of possibilities"...not very specific at all.

Going to look at the easy stuff first...spark plugs...as well as a visual inspection of everything.

Question is...anyone know or have experience if there is a "most common" source/cause of the P0303/P0306 codes?

Thanks Much.

 

P0303 and P0306 are cylinder specific misfire codes. Misfires can point to general maintenance issues (worn spark plugs, failing coil packs), fuel trim issues (vacuum leaks, engine sensors etc), poor quality fuel (do you regularly run a name brand premium 91+ octane (US)?

If you don't know the full service history, you may want to start with a baseline tune up - oil change, 93 octane gas, fresh OEM plugs with the correct gap. Then I'd consider swapping coils - ie swap #2 and #3, #5 and #6 to see if the faults move to P0302 (mistire on #2) or a P0305 (misfire on #5). Next is to do a visual inspection of vacuum lines etc. You can also consider popping off the intake hose by the MAF and giving it a look to see if there's any dirt/oil in the tubing. This may point to a failed oil separator in the PCV. If you decide to clean the MAF, don't use carb cleaner, use a product like CRC MAF cleaner so as to not damage the wire grid. Check to make sure there are no loose air hoses/cracks etc. You can also try spraying around with some flamable carb cleaner etc to see if any gets sucked into a crack or seal.

 

Thanks for the reply mt6127.

I started with the easy stuff. Got some new spark plugs yesterday & installed them today. Cleared the OBD II codes...and took it for a short drive. The "Check Engine" light has not come back on yet...will have to use the car for at least 2-3 days to get some regular driving on it...and see if the check engine light comes back on.

Hopefully the check engine light does not come on. If it does...I did consider replacing all the coil packs as a next step.

By the way...in your reply you mentioned codes P0302 (misfire on #2) or a P0305 (misfire on #5). Does the last digit of this code refer to the engine cylinder with the issue?

If so...the codes I got when I scanned were P0303 and P0306...does this mean that the issue was with cylinder's #3 and #6?

Thanks

 

One other thought I had. It seems unusual to me that 2 of the cylinder's threw these codes at the same time.

Logically to me...2 cylinders throwing a code at the same time would seem to point to an issue that's not individual cylinder related (not individual spark plugs or individual coil packs)....I would think it would have to do with something that would effect all cylinders.

But if this were the case...then why would only 2 cylinders be effected (#3 and #6)...and not all 6 cylinders?

I'm just thinking out loud...any ideas anyone has...or experiences anyone has had are welcome.

Thanks

 

Yes the last digit in the 030X codes are specific to the cylinder (with #1 being closest to the timing cover). My general sense is if you get a single code, first thing to do is to swap coils to see if the fault moves to a new cylinder (if it does, replace that coil, not the whole set). If you get multiple codes or a generic 0300, then I'd look for fuel trim issues - ie intake air leaks, dirty MAF etc. Also as you've already done, its helpful to clear codes to see what returns. You may also want to drive it a bit hard or take up to highway speeds, particularly if you suspect a coil (a weak coil will have trouble keeping up but can be quiet when puttering around town. So it seems you're on the right path. Post up how you make out.

 

All great ideas & suggestions (thanks).

Just scratching my head why 2 codes for different cylinders came up at the same time.

* Hard to believe 2 spark plugs or 2 coil packs could have gone bad at the same time.
* And if it is an issue that would effect all 6 cylinders...why I didn't get 6 codes (1 for each cylinder).

 

exactly! If you get one code, you can suspect a coil or plug. Two codes suggest something that may impact all cylinders like bad fuel or an intake air leak - its just those two that are most sensitive and tripped. Airflow is not identical to all cylinders and engine temps can vary as well. The misfires are detected by the knock sensors - which are really strategically placed microphones that listen for pinking or similar noises so that's how the ECU knows 1 to 6. So one more suggestion - try running a brand name 93 octane (US) gas or throw in a can of Techron injector cleaner to see if that may help. Usually running one or two tanks of 93 has enough detergents to clean up any injectors (assuming they are not damaged).

 

Just swapped out all 6 coils...no luck...check engine light returned (after clearing it). Given the 2 codes...pretty much figured it wouldn't be as easy as new plugs & new coils...but it was an easy thing to try.

Just did a fuel fill up (have always used brand name fuel & always use 93 octane)...probably good time to try the fuel injector cleaner idea.

Will give the other ideas a try as well.

Thanks

p.s. By the way...something else I should mention. Car seems to run rougher than normal during startup (first start after sitting overnight). Also seems to have the occasional hesitation when driving after fully warmed up (thus not a cold-only or warmed up-only condition). But an occasional "engine roughness" is there while driving (maybe happens 2% of the time while driving)...definitely not a continuous 100% of the time roughness issue.

 

Not surprised that the coil packs were not the solution. I hope you didn't drop $200 to find that out. How does the wiring harness to the coilpacks look?? This really sounds like a fuel trim issue to me - possibly due to a vacuum or intake air leak, issue with fuel pressure, a specific sensor (coolant sensor is on my suspect list - any odd behavior with the temperature gauge?) Hard cold starts suggest low fuel pressure - pump, pressure sensor etc. Next is the electronic throttle (ETM) - which was a common fault in the early 2000s but I dont know if that's common to a 2008. Any rate check out Xemodex's web site for ETM faults and diagnostics. Last thing is compression. this could be a stretch but any signs of oil consumption or coolant loss or cross contamination that would suggest a head gasket issue or piston rings? Again not a likely scenario.

 

Thanks much for all the possible ideas.

Regarding the coils. Have 30-day no questions asked return for them...I made sure of this before purchasing...thus no $$$ lost giving new coils a try.

* Wiring harness to coils looks fine. All insulation in place...nothing melted, burned, cracked, or frayed. All connectors in good shape.
* No problems with temperature/temp gauge.
* No hard starting issue (engine does run more rough than usual until warmed up).
* No coolant loss issue...no oil consumption issue...no oil/coolant cross-contamination issue.

Going to try the fuel injector/fuel system cleaner next. Purchased a 6-pack of the Chevron Techron. Of course this solution may take a while to show any results until a bunch of fuel has run thru the system.

Thanks again for all the details & ideas.

p.s. Do you have a link to Xemodex's website in case I have trouble finding it (don't think I've been there previously)? Thanks

p.p.s. In case it helps...2008 Volvo S80 has about 110-112k miles on it (not too bad for a 15 year-old car). I see lots of used cars on my local Craig's List that have 150+k miles...and only 5-7 years old.