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Old 07-19-2010, 12:24 AM   #1
tylerjoe500
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Default 2003 saturn L300 codes p0050 & p0300

car has 80000 miles on it and it will not go over 10mph. i replaced the corresponding 02 sensor for the p0050 code but code is still present. these are the only codes the car throws but it runs horrible. where do i start??? ive checked plugs and all look great. the boots on the coil packs looked great too. i suspect bad cat converter so i cut the pipe in front of cat to test and no difference. could that be because of lack of back pressure now? if cat is fine then what else? EGR valve maybe? any way to test or check them easily? any suggestions? thanks

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Old 07-19-2010, 03:40 AM   #2
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Default Re: 2003 saturn L300 codes p0050 & p0300

An open exhaust (no back pressure) won't affect engine running as severely as yours is doing. The heater code for the O2 sensor may be just loose connections. The P0300 means a general misfire condition that's pointing to all six cylinders. With electronics running the engine, its going to take some more time diagnosing your issues.

Isn't there a SES/engine and reduced power indicator lit up on the instrument panel displays? A severely restricted engine running 10mph seems to be in reduced power mode that should be generating error codes as well as lighting up one or more indicators. Please post more car info like mileage, last maintenance done. And where did the code reading come from? Generic code readers may not read special codes unique to GM/Saturn and require better readers.

Our engines use a mass air flow (MAF) sensor that sometimes fail and can cause similar symptoms. It sits between the air filter and throttle body and has a wiring harness. Removing it for disassembly and cleaning it with CRC MAF Sensor cleaner may restore full engine power as one way to test the maf sensor. Be sure to clamp the flex tubing carefully as any vacuum leak can cause major air flow issues that can cause severe engine running issues. Any maintenance done with removing the intake runners and creating a break in any flex coupling can cause vacuum issues altering the air fuel mixtures.

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Old 07-19-2010, 03:47 AM   #3
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Default Re: 2003 saturn L300 codes p0050 & p0300

80,000 miles. five thousand miles ago driving down road ready to pass a semi i stepped on it and reduced power light came on. had code read at autozone and said MAF sensor. i bought one and replaced and light went off for a week or so then back on. i stupidly put it off because its my in towner car. less than 5 miles a day for most of the year. but recently it would spit and sputter at startup then come out of it. now it dont go at all really. the SES light is on at start up caused by the p0050. then the SES light will blink when it misfires (p03000. then back on steady. it seems to me that maybe the MAF going bad screwed up my front precat converter maybe? the car goes faster (but still misfires) when i remove the O2 sensor above this cat.

also the boots on the intake are inexcellent condition and i did the (carb cleaner spray test) to check for vaccum leak.

another note i checked compression and all is good there as well as fuel pressure. but i dont know if fuel pressure is supposed to slowly drop after car is shut off? it stays constant running but slowly drops down after engine shutting off. i also replaced fuel filter.

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Old 07-19-2010, 04:07 AM   #4
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Default Re: 2003 saturn L300 codes p0050 & p0300

In-town driving and not having the engine heat up may cause sludging issues if water amd moisture isn't allowed to boil out of the oil. A plugged pre-cat can cause engine constipation resulting in false error codes. Try Cleaning the maf sensor as this is the only way for trial and error diagnosing maf sensor problems short of visiting Saturn/GM. If enough crud gets back to the throttle body, this may affect engine running too. Our throttle bodies aren't easy to remove for cleaning.

Try reading threads about other L300 members having similar issues especially with clogged cats.

I wouldn't be concerned about fuel pressure bleed-off. Steady fuel pressure with the engine running is more important since pressure beed off doen't affect a dead engine. It may hurt start-ups but allowing the fuel pump to run its primimg cycle during the 2-3 second cycling at ignition ON time before cranking the engine is all that's needed to ensure fuel pressure is available to the injectors.

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Old 07-20-2010, 02:43 AM   #5
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Default Re: 2003 saturn L300 codes p0050 & p0300

ok ive pretty much ruled out the cats. car runs the same with or without the O2 sensors in before the cats. my next question is how do i rule out timing chain? is there certain signs that it is slipped a tooth?

also at idle the car seems and sounds fine. it idles real smooth and doesnt miss a beat. its only when i start excelerating that the misfire code pops up.

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Old 07-20-2010, 03:48 AM   #6
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Default Re: 2003 saturn L300 codes p0050 & p0300

A good compression test tends to rule out timing issues and since you're close to 100k, the timing belt will need to be replaced. Something to think about and covered in past threads with pictures and procedures. With average mileage use and normal maintenance the issues seem to about the engine sensors that plays a large role in engine running. Without a scanner to monitor live data and understanding how to interpret them, you're left to guess which ones are faulty.

The major sensors are; maf, map, tac, app, and a few others. Each one has a specific purpose and may not generate error codes when they deteriorate. Failing outright is one thing but a sensor deteriorating may not cause error codes to light up the SES indicator. You're left to either invest in a good reader/scanner and learn about troubleshooting OBD II codes, observe live data streams for erratic sensor behavior or have Saturn diagnose this issue as they will use their equipment to isolate a problem.

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Old 07-20-2010, 09:46 AM   #7
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Default Re: 2003 saturn L300 codes p0050 & p0300

wow, everywhere else in this forum i see that people ask questions and they get pretty good answers. not me, i ask questions and the only one that answers me pawns me off on a saturn dealer and just blows off that im reaching for help here so i dont have to spend 5000 to fix this stupid ****ing car.

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Old 07-20-2010, 10:53 AM   #8
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Default Re: 2003 saturn L300 codes p0050 & p0300

Not sure about trying to blow you off as I'm not one to suggest a dealer unless its appropriate as I've suggested some things to you that are going ignored. Those suggestions deal with sensors that are part of engine operations otherwise it would be be easier to troubleshoot. I don't think you'd like me to suggest replacing the sensors I posted about previously as they are the ones I would look into without more error codes. I'm merely pointing out what I consider the parts that may be causing the reduced power issue. I cannot tell you to start throwing parts at your car nor does anyone else here.

And if you noticed, I too have the same year and model as you have but if you think I'm pawning you off to a dealer, that's strictly your opinion as it was not my intent.

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Old 07-20-2010, 12:10 PM   #9
tylerjoe500
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Default Re: 2003 saturn L300 codes p0050 & p0300

i told you initially i had reduced power light months ago, car has been normal after that light cleared. a reduced power light is no longer an issue. just misfire if you could possibly give me a few reasons as to why a motor randomly misfires, that would help. im touchy about dealers expecially since the closest one is 90 miles away. there is no one in this town who will touch my car mechanically. wees a buch of hicks here. sorry about the attitude but ive been trying non stop for 4 weeks straight trying to eliminate things to figure this out. im just a little peturbed.

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Old 07-20-2010, 01:33 PM   #10
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Default Re: 2003 saturn L300 codes p0050 & p0300

Here in the Big Apple we have dealers to the left and dealers to the right but no Saturn dealer near me. I never trusted a dealer after buying my first new car back in '77. My Saturn dealer closed about a year after I bought my '03 L300 in '05. I learned more about Saturns here than from my FSM's.

It wasn't clear when you last had reduced power mode so I presumed this was still part of the misfiring issues. The throttle actuator control (TAC) module and accelerator pedal position (APP) module has a direct effect on turning on reduced power mode as well as the maf sensor.

Misfiring can be from;
a)The maf sensor since it measures air volume for the ecm to determine air/fuel mixtures. An air leak occurring behind the maf sensor can cause lean air mixtures.
b)The map sensor since this measures relative intake manifold pressures for the ecm to determine a/f ratios. A clogged sensor will cause strange engine running that isn't clearly defined.
c)Worn out spark plugs even though they're not due for replacement until 100k miles. Bad gas causing premature wear/deposits?
d)Clogged catcon/pre-cat.
e)Loose electrical harness connections.
f)Loose ground connections.
g)Worn out/cracked flex couplers to each intake manifold and main manifold allowing in extra air to lean out a/f mixtures.
h)Faulty coolant sensor. This one's rare but not impossible.
i)Intake air temperature sensor. (built in to the TAC).
j)Clogged fuel filter; lowering pressure or restricting flow to lean out mixtures.
k)Faulty fuel pressure regulator by lowering pressure to lean out fuel mixtures.

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Old 07-21-2010, 02:47 AM   #11
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Default Re: 2003 saturn L300 codes p0050 & p0300

ok so i decide to start from scratch and go down your list you have made for me. i start with the MAF sensor. i disconnected the intake tube to the throttle body and watched the self check it performes with key on and that looked normal. so i started the vehicle with this tube off. It sounded great. i could rap it up and everything. so i take it for a spin. the vehicle runs like a raped ape, until you slow down then the engine dies, probably due to wrong readings from the MAF sensor, so i unplug the sensor and it quits dieing. sounds and performes like new!!! i put the intake tube back on and no change (which rules out obstruction in the intake tube/airbox/ ect.

so i look back on where i got the maf sensor from that i replaced a while ago. i got a used one from a saturn wagon that was totaled out. this sensor was same part number and everything.

my next question is can this sensor being from a different "computer system" be programmed different than what mine would be? or did i just get a bad maf sensor? i havent bought a new one just yet i have to wait til payday.

But for right now the problem seems to be having that MAF sensor plugged in.

I should also add that with the sensor unplugged i still get the p0050 code. the misfire code is GONE! and i do get the code for low current in the MAF sensor.

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Old 07-21-2010, 06:07 AM   #12
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Default Re: 2003 saturn L300 codes p0050 & p0300

Well, I did mention cleaning the maf sensor back in post #2 as maf sensors measure air flow volume that has a direct influence on the air/fuel mixtures. Since carburetors went the way of dinosaurs, every electronic sensor now takes the place of any mechanical hardware that used to be connected to the engine block. The only sensor never changed is the oil pressure sending unit.
Maf sensors doesn't have any computer in it for programming and is basically plug n' play. The best you can do is try cleaning it to see if it improves engine running before replacing it. Some sensors use Torx theft deterrent screws that can be vise gripped off - there's a little shoulder to grab on to with sharp jaws.

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