Saturn 2005 Ion chronic check engine light problem

We’ve had the Check Engine Light go on and off every few days for a YEAR now. Mechanic can’t diagnose or fix. Code always returns as Random Misfire. Have tried reprogramming computer twice, flushed the engine once. Notice that it goes away with lots of highway driving but always comes back when we are in town which is most of the time. Rarely get on the highway. Commute is 5-7 miles. Manual transmission. Our repair guys are stumped. Any advice? Other than new repair guys? They have consulted with local Seattle GM dealership who have done the reprogramming. Car runs just fine! No problems apparent other than the light. They say the next thing we should try is replacing the ignition coil. Nothing has yet worked and this sounds expensive… Could the Check Engine Light itself be faulty?

2005 Saturn
Manual Transmission
Ion , Ion-1, Ion-2, Ion-3, L300, Relay-2, Relay-3, Or Vue ?
Approximate Number Of Miles On Vehicle ?
When Discussing The Engine It’s Helpful To Know Which Engine Is In The Vehicle.

What esle has been done besides reprogramming and an “engine flush,” whatever that is ?
Recent OEM spark plugs and plug wire set ?


56,188 miles. Manual transmission. 2.2 L engine.
Yesterday, 3/28/13, engine flush per invoice is "motorvac injection decarbon service"
April 2012, per invoice reprogrammed power train management computer
March 2012, per invoice, engine diagnostic pinpoint testing, removed and inspected spark plugs, replaced spark plugs, reprogrammed computer

We sort of gave up for a year and lived with the CE light after a couple more checkins where they couldnt get a code other than random misfire. Yesterday’s service made no difference. Sorry am not car savvy enough to know what else I should share! Thanks for any advice or more questions!

The CEL is controlled by the ECM, the engine computer. If there is no actual misfire, then it’s a good bet the ECM is generating the false trouble code…When was the last time the spark plugs and wires were changed? Is passing an emissions test an issue here?

Spark plugs replaced when issue first surfaced, a year ago. Not sure about wires , is that normally also replaced when spark pugs are? We passed emissions about 9 mo ago, happened to be a few days when CEL was off and our fingers were crossed. So we are good for another year or so there.

@Kables please post the exact fault codes.

If that misfire is legit, the catalyst may suffer in the long run.

Just so you know, some misfires are fuel related. A partially plugged injector could cause this. An electrically open injector could cause this. I’ve seen both.

Perhaps it’s time for another shop.

Sometimes a new set of eyes sees something that the other guys missed. Or perhaps somebody will analyze the data differently . . .

Thanks db4690. The code that keeps coming up is PO300. They tell me this is just a “random misfire” code and can’t provide any other info about what it means. But they also say when they pull this code they check and can’t detect any misfire problems in person (I’m not sure what they check, though).

The very first time this problem surfaced a year ago, they pulled the PO300 code as well as a PO171 - “fuel system too lean” code. Research on that code led them to recommend reprogramming the ECM. I don’t believe this code has come up again.

I agree it’s time for another shop. We really like these guys but they seem to be at a dead end. I’m wondering if it would be worthwhile to go to a GM dealership rather than a local shop, which is what we usually prefer…

Thanks for any additional thoughts you or others may have!

@Kables I believe I found a factory fix for your car.

That shop might be able to perform this procedure. But I’m not sure how they’ll react if you present them with the “solution” . . . it’s supposed to be the other way around.

No guarantees this is the silver bullet, either. But both of your fault codes are included in this TSB.

Don’t let anyone talk you into adding fuel cleaner to the tank instead. Hooking up fuel cleaner directly to the fuel rail is much more efficient and direct.

First off, you need to use a shop which has a factory scan tool for your car. And a lab-scope. Possible causes of misfires are

  • Spark plug
  • Fuel injector
  • Ignition coil
  • HV ignition wires
  • Compression problem
  • Air/fuel mixture (esp if it is lean)
  • EGR or PCV problem
  • Cooling system problem
  • ECM

Make sure all the routine maintenance suggested in the owners manual is up to date. Esp the spark plugs, the engine air filter, and the fuel filter. For spark plugs and injectors, sometime even the coils, your mechanic can move them around and see if the problem tracks the move. If you haven’t had a compression test done, that would be in order. Test the PCV and EGR at the same time, both are inexpensive tests. A rail fuel pressure test is a good idea also. If testing shows no other problems with the above, probably a course of diagnostic parts replacement is in order. The coils and HV ignition wires would be a good start. Be aware that this may prove difficult and expensive to solve. Comes with the territory when a lot of hi-tech is designed into modern cars.