service engine soon light

**Big D Squared** · 07-07-2012, 04:26 PM

My service engine soon light just came on today and I can't figure out why what is usually the problem when that light comes on?

**nathanWS6** · 07-07-2012, 04:57 PM

more than likely it's an O2 sensor malfunction if it's still running ok... go to local auto parts store and they will scan your car for free

**pajeff02** · 07-07-2012, 05:38 PM

Actually, it could be lots of things. As posted, run it down to the parts store and let them scan it for you. Be sure to write down the code (or codes) that come up and then post them up on here. The code will start with the letter "P" followed by 4 digits -- ie. "P0101". If your check engine light is flashing, rather than steady, do not drive the car!

**Guerrillakilla13** · 07-07-2012, 06:28 PM

like Jeff said, it could mean a lot of things. But yes most likely, if you haven't modded anything, chances are its most likely gonna be the cats. Tell us what code the guys at the auto store give you when you run it.

**Big D Squared** · 07-08-2012, 05:11 AM

Got the code from AutoZone this morning it is p0420 the guy said it was common on these cars but what do I do to fix it ?

**nathanWS6** · 07-08-2012, 05:30 AM

converter on driver side not working efficently or rear 02 sensor bad.. cheapest is O2 sensor replace but don't know till replacing it.
also have them clear code. sometimes with that one it won't comeback when cleared out..

**Big D Squared** · 07-08-2012, 05:38 AM

How much does it usually run to fix the o2s and how much does the catalytic converter cost and could it be my maf

**pajeff02** · 07-08-2012, 06:32 AM

P0420 is a catalytic converter efficiency code for Bank 1 (driver's side). Essentially, the rear O2 sender is looking at the level of oxides in the exhaust stream and what it is reporting back to the PCM is out of spec. Possibilities are a bad converter, a defective sender or a wiring issue. There is no harm in driving your car with this light on as the rear O2 senders do not impact fueling. You could swap the rear O2 senders from left to right, reset the light, and see if the code comes back on the driver side, or if it moves to the passenger side. That will tell you what is actually the problem in most cases.

**nathanWS6** · 07-08-2012, 06:34 AM

no it's not the maf.. 02 sensor is about 65 if you do it yourself.. cats are around 150-200 just for one side if your leaving it stock..

**pajeff02** · 07-08-2012, 08:51 AM

OP - if it turns out to be the cat, I have GM replacements from my car with around 20,000 miles on them. The factory cats were subject to an extended warranty program under which mine were replaced according to the GM service records tied to my VIN.

**JayTA98** · 07-08-2012, 02:50 PM

OP like jeff mentioned don't go buy a converter yet until you figure out if it is the sensor or the converter. The easiest way is to swap the sensors as suggested. Just unplug the rear sensors(the ones closest to the rear of the car)grab a wrench or o2 sensor socket and swap them. reset the codes and it will come up eventually again if not instant. get it scanned and if it is the same code then the problem could be the converter among other things. If the code now is for the other side then you know is the o2 sensor because it followed it. Then you will only need to buy an o2 sensor. Is fairly easy to do.

**Smittro** · 07-08-2012, 03:02 PM

I agree with the guys about swaping the 02's around to see if the issue follows.

To add,, from my own research when my cat died the common mileage seems to be 80-100K+ to lean towards it being your cat/s.

If your mileage is low then it could simply be a bad rear 02 sensor like Jeff and Jay stated.

Something simple like a stray rock or road debris could have struck the sensor and damaged it.

Simple to check and easy to correct. Good luck let us know what you find.

**Big D Squared** · 07-08-2012, 05:50 PM

Yeah I'm going to swap the sensors probably Thursday maybe earlier but I'll let everyone know as soon as I change them

***SMWS6TA*** · 07-09-2012, 12:32 PM

Bad CAT = time for LT headers and ORY

**Big D Squared** · 07-13-2012, 02:35 PM

So I took the drivers side o2s off and tried to take the passenger side off but couldn't so just bought a new one from the drivers side light went off everything was good thanks for all the help

**SuperSSguy** · 07-13-2012, 05:01 PM

^^ Just a bit of friendly and been there done that advice, get yourself a code scanner..They are not that much and come in a variety of models and prices! They are invaluable when it comes to our LS`s...That way you can get your own codes and clear them whenever you want! and in the futeure when you mod up youll be set!!!

**pajeff02** · 07-13-2012, 07:13 PM

^^ Agree.

**SuperSSguy** · 07-13-2012, 10:13 PM

Just curious to know if 02 sensors can be ''cleaned''?

**Big D Squared** · 07-14-2012, 06:59 AM

Ok so I changed the o2s and ran fine for two days now this morning the service engine soon light comes back on fml now I'll have to change the catalytic converter not cheap this sucks just bought the car and having this much trouble and I'm getting a buck when pushing down on the clutch in first idk what to do I guess it's time for a mechanic to just do a full inspection

**nathanWS6** · 07-14-2012, 12:53 PM

if it were me (and i had the same issue with mine) leave the converter on till you can get some LT's and ORY.. will solve the problem and give ya some more getty up!!