2008 Buick Lacrosse CXL

My son said the Oil pressure low light came on when he tried to start the car. It didn’t want to start.

When I got there two hours later, it started but had a check engine light. But no low oil pressure light.

Sounded like it was missing.

Code from computer came back P0300 “Random/Multiple Cylinder Misfire Detected”

I cleared the code. Reved the engine to about 2000 RPM’s and the CEL came back on.

Same code. When idling it feels like it’s missing.

The plugs look good, I am going to replace the ICM.


Thank you!
Will let you know how that ends up tomorrow.

Though a plug looks good, it could still send a fault code. For the price, I’d change them out to eliminate this.


It’s such a pain to get to the back ones.

Am I wrong on that?

Hell I can barely see them, let alone take them out.

It’s not the spark plugs.

Random multiple misfires detected means there’s misfires occurring in more than one cylinder. And what are the chances those spark plugs all took a crap all at one time?

You want look for a common problem that can cause those cylinders to misfire. Something like is the fuel pump providing enough fuel pressure to the injectors?

It’s not the ignition module either. The ignition module either works or it doesn’t.

But here’s another common thing that could cause the misfire. The ignition module receives a signal from the camshaft position sensor. The ignition module takes this signal and then determines what coil should fire and when.


I read somewhere online that some one had the same problem.

"Thanks- I just found some other information. I checked the spark and there is no spark on wires 1 and 4(lower coil). I switched the coil pack and the problem is still on 1&4, so It points to a bad Ignition Control Module. I get 12V on the lower pin of the primary, but most likely no switching on the other pin(didnt check that, but the known good coil worked so it must be bad. Is there any other reason that would cause this? I’m thinking it has to be the ICM?
Thanks Again

jerryls09-13-2012, 01:46 PM
It was the Ignition Control Module. I swapped it out and everything is fine. Simple job, 3/16" socket to remove the coils and a 1/4" socket to remove the connector. I bought a used one on ebay for $36.00. GM uses that same module since 1994, so there are a lot around.
Thanks for everyone’s help."

Glad you found it. On some of those tight fits in the back, I end up taking the coil off to get better access. Even with skinny arms I have a problem.

Replaced the ICM (140 bucks) and the baby is running smooth.


No CEL and a nice smooth idle.

Tester said;
It’s not the ignition module either. The ignition module either works or it doesn’t.”

You are wrong sir.

Have a great day everyone.

And thanks for the feed back.

Right or wrong the rates are pretty reasonable.

Yes they are. :slight_smile:

But he almost convinced me.

I still went with my first impression. And I am so glad it worked.

Not that it always does :frowning:

But that is the nice thing about forums, you can get all kinds of advice.

More than I could when I was in my teens… and there was no such thing as the internet.

Thank you all again.

No gloating Ramsforever, you may have just gotten lucky and next week the problem will be back, and you’ll be asking the same questions.

@Tester; Is normally pretty accurate and reliable.


I’m going to agree with Yosemite and Tester on this one. I think you will be seeing this come back on you as the camshaft position sensor and crankshaft position sensors tend to be very intermittent when they first start to fail.

I’m going to lean toward the camshaft position sensor based on your mention of the 1/4 coil. There is a plate under the 1/4 coil that senses the differences in the voltage level between the 1 and 4 side of the coil to determine which cylinder was under compression at the time the coil discharged, at least that is the scheme that GM uses on some of its vehicles with the lost spark ignition system.

That plate is pretty reliable and almost fool proof, but an intermittent spark from one of the spark plugs or a defective wire, or even a slight crack in one of the coil towers will throw off the signal. If you hadn’t mentioned the coil pack, I would have jumped on the CPK (crankshaft position sensor) because of problems that Buick has had with them in the past, although it was the distant past when they used to locate the CPK behind the crankshaft pulley. They moved it to a more protected location and I don’t think they have has as much trouble with them since.


I will keep an eye on it and let you know.