Hey everyone!
I'm new on here and was wondering if anyone could give me an idea on what the problem could be.
I'm getting 3 codes, p0300,P0171 and p0174.
I'm currently living in Sweden and on my journey over here from Spain I had some trouble with my car. I have a magnuson supercharger fitted and the coolant reservoir that cools the supercharger cracked open while I was driving (I haven't got a clue how). This resulted in the car over heating and warping the cylinder head. At this point I was in Germany so I had the choice to call my Insurance company and get it taken back to Spain, or carry on driving. I carried on for another 15 hours until I reached Kalmar in Sweden. I took my car to get it repaired. They skimmed the heads and changes all gaskets and ofcourse new plugs.
They don't seem to know what the problem is. I now have the car back and would really like to get this problem sorted.
Any ideas?

 

Does it run okay now? If so, have you tried clearing the codes to see if they come back? Quick search says P0300 is a random misfire; the other two say fuel system too lean. Look at this:P0171 and P0174 - OBD-II Trouble Codes

 

I've been looking into superchargers for my 08 but posts like this scare the heck out of me.

I wish you luck, but you might want to start over with a new engine. I had a guy w/ 200k on his escalade and needed a new engine and the dealership only charged $5000.

 

Hey. Thank you for your replies. I've done loads of research online and I'm being told it's most likely a vacuum leak but like I said, the gaskets have all been replaced and I can't see any broken pipes anywhere. Being In Sweden, there are no parts available. I need to order everything from the US which is a bit of a pain as it takes a couple of weeks to get here. I don't think I need a new engine. I was told that the bottom end was in perfect condition and only one head was damaged. I got the mechanics to remove both heads and get them both rebuilt with all new parts so the engine should be perfect now. I'm guessing it's a sensor, something electrical or fuel. The car is an 04 with only 20,000 miles. I spoke with magnuson and they sent me the updated reservoir with all the connections which is now on the vehicle. Surprisingly the supercharger wasn't damaged from the overheating.
Don't let this put you off getting a supercharger. A standard hummer is so sluggish, a supercharger really brings it to life with the power always there when you need it. When I was living in Spain, two of my friends also had h2's that were supercharged and after all this time, this is the only problem we've had. I hope I can get her fixed before the Swedish winter hits me. I've just ordered the 4 oxygen sensors as I've also red that this could be the problem. I can't see how it can be but there not expensive and I can change them myself so I thought it would be a good place to start. I have tried erasing the codes and only the p0300 comes back. It's missfiring like crazy when It idles, but while I'm driving it seems fine although now and again the engine light will begin to flash.

 

Take a look at this experience regarding CATs the clue may be in p0174 "bank 2" i.e. only one bank is affected. Any coolant or oil that got into the CATs could create this issue.

It may be unrelated to your problem but the multiple P codes is kind of similar. In my case it was bank 1.

Perhaps someone in the forum could advise a way to tell if a CAT is plugged ... without tapping it that is!

Good luck!

If your CATs have been removed then ignore this suggestion

 

Thanks fo your message oceanbrave.
Around 5000 miles ago I changed the drivers side cat and I've just changed the passenger side cat but never the sensors as I was told it wasn't necessary. Identify think the cats will be plugged in such a short period of time which leads me to believe it could be the 02 sensors. I should have them next week so fingers crossed they fix my problem. Thanks again for your advice. If.he sensors dont change anything,then il have to take a look at the drivers side cat. It might of gotten damaged when I warped the cylinder head as oil,coolant was was pouring down my exhaust.

 

Here is a good video on which may help with diagnostics if only to rule out a cat problem. Eastern Catalytic (EC) is a good source of info.

On one hand I hope it isn't a cat problem, on the other its not a big problem.

Regarding the O2 sensors, following EC's videos I changed all mine. As for brand some folk said use the same the ones fitted but it proved difficult to read the P/Nos in place. Anyway I used Bosch which were fine (RockAuto) and not too expensive. I also bought the special wrench and thread chaser which proved invaluable, again cheap.

Note your error code is Bank 2, is this not the passenger i.e. RH side?

 

The codes I'm getting are both bank 1 and bank 2. I also used RockAuto and I bought the bosch ones along with that special 02 sensor socket. I'm really hoping that these sensors do the trick. Il watch that video once I get home. Thanks again for your help!

 

Does seem fault codes suggest a common cause and so maybe not CATs.

Keep us posted..

 

I received the sensors on friday so I went down to a friend's garage yesterday and began fitment which wasn't as easy as I thought. All 4 sensors were basically welded on so we had to remove both converters and heat them up to remove them.
Once all this was done, I deleted the codes and started her up. It ran like a bag of **** even worse thanbefore. I really gave up and began my journey home with the engine light flashing. After about 5 miles down the road, the car coughed out a big cloud of smoke and all of a sudden the engine light went out and started to run better. By the time I got home the engine light was completely out. I will run her today and hope for the best. Maybe I just need the sensors to start reading correctly. I thought it would be pretty instant but obviously not.
Il let you know what happens today!
Thanks again for your help and opinions