Service Engine Soon light

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A little research goes a long way.  Would you believe there is actually a forum for OBD II codes?  From that source Driftless Shifter, you are right - check the wiring first.  Then, thankfully, the 8.1L engine is not one where Chevy put the sensors under the intake manifold.  Instead, a couple of GM mechanics have told me it is on the lower left side of the engine (verified by the 8th letter in the VIN being a G).  I am assuming  (hate that word) that the "left" side of the engine is as you face the front of the coach.  I have now gotten suspicious because the former owner told me he suspects it was a "Knox" sensor before I ever had it checked out with an OBD II.  This tells me he had the problem before and did nothing about it - Probably just cleared the fault.  Still - not bad if that is all that is wrong on a 12 year old coach.  He did confess it has sat for the last 2 years in covered storage and it is really peppy on the highway.  We test drove an old Pace Arrow with a 460 Ford and you needed ear plugs for that screamer.
 
You know old gas loses octane as it ages? Follow me here. What happens when you put regular gas in an engine that requires hi-test? It pings and knocks. Sounds like a bucket of marbles under load.
Your knock sensor senses it.
Tells the ECU.
ECU retards ignition spark timing to reduce knock.
Knock sensor still sending knock signal.
ECU has pulled out all the ignition timing it's allowed and throws a code, blaming the knock sensor.
If it was parked for 18 months, and rarely used, some gas from 3-4 years ago is in the mix. Either drain it or practice driving your new rig locally, on familiar roads. Get your co-pilot comfortable with the wheel too. Do it like I posted earlier, with top shelf fuel system cleaner.

Bill
 
Bill N said:
Well here is an update on my particular SES light.  I pulled the MH out of storage today and on the way home I stopped at an OReilly Auto Parts store and had them read out the Diagnostics on the SES fault.  In 5 seconds, the young man told me it was a code PO327 Knock Sensor Circuit 1, Low Input.
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Did he erase the code for you? That's the type of code I would want to erase and see if it ever comes back again before doing anything at all. To erase it, it only takes a press of a button from any OBD2 reader and then the MIL will go out and stay out until the problem is detected again.

-Don-  Reno, NV
 
Many things can cause a knock sensor code. That's why you need a scanner, not just a code reader. You also have to know what the scanner is telling you. Some scanners have graphs and record mode, so you can hook it up take it for a drive and either look at the graph or down load it to a pc. I would guess it's NOT a bad sensor, but something is causing it to throw the code. Poor or OLD gas, injector plugged up, plugged up fuel filter, vacuum leak, even a bad idler bearing could cause this. When the light is illuminated the timing is locked at 0 degrees advance, poor performance and terrible fuel mileage will result. It's already been mentioned, but I'd drain as much fuel as possible, and add some premium fuel and the correct amount of sea foam to the tank, and drive it. With a scanner hooked up you can see  how many knock counts the pcm is seeing, if it's got knock counts just sitting there idling, you need some one with a stethoscope to see where the vibration is coming from. Even an exhaust manifold leak could cause this.   
 
I should have had the auto parts store guy turn off the light but being a novice at this (a very old novice), I did not know he could do that.  I ordered my own OBD II but it will not be here for a while so when I took it in for an oil change today, I had them check the fault and do checks on the wiring and they found nothing and turned off the light to see if it would come back.  I finally have enough of the old gas burned off to add some premium in and will do that tomorrow on the way back to storage.  But with 41 mph winds forecast for the whole day, it may be a wild ride.  Got run off the road today by a wide load on a very narrow road.  First thing I saw was a large length of cement sitting crossways on a semi bed and into my lane about 4 feet.  The ditch was fairly steep but I squeezed as much of it over that I could and just barely missed being cut in half.  The SES is off for now and I am hoping it stays that way but if it comes back, the shop says bring it back and they will replace the sensor with no further diagnostic charge - Gee how kind.  I know this gas is old but the engine is not giving any clue that it is being affected.  In fact, it is running like a banshee - the wife followed me the other day and could not believe how fast the thing was going (she didn't notice the white knuckle driver) ;D
 
Bill N said:
I should have had the auto parts store guy turn off the light but being a novice at this (a very old novice), I did not know he could do that. 
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Even the cheapest readers can erase the MIL.  But it might take a while for it to come back, such as several says of normal driving. So don't get your hopes up that the problem is gone until you don't see the SES light up again for a couple of weeks.

BTW, check here for what to check with a PO327.

-Don-  Reno, NV
 
If a parts guy or girl  cannot erase your code: "store policy", ask them if you can follow the bouncing prompts. this will remove their
liability.... and ur code.  8)

Dan
 
I had a similar problem with my 8.1 liter engine in my 2003 GMC Sierra HD.  When the engine was worked very hard (pulling my 5er up hill) the check engine light would occasionally come on and stay on for a few hours to days - and then go out by itself.  The problem was traced to a defective airflow valve assembly located off of the air filter box.  The defective valve was changed and the problem disappeared.
 
Get rid of the gas, before you let anybody go further than replacing knock sensor. I'd put money on bad gas.
Really, I would. :)

Bill
 
Well after accumulating mileage by bringing the coach from the seller to storage then to the house and around the area for oil changes and SES diagnoses, we got the light reset without replacing any knock sensors and added a large amount of stabil and 30 gallons of fresh gas and put it back in storage.  The light did not return in the past 50 miles.  Also, our own OBD II reader arrived in the mail so I should be able to do some diagnoses if the light comes back on.  This was a valuable exercise because I now know a lot more about the SES, Knock Sensors (including their exact locations on the 8.1L), OBD II readers and the possible causes of the fault.  My thanks to all who contributed to this thread.
 
This thread reminds me of an "Service engine" light experience I had on my 2005 Dodge Ram many years ago.  We pulled our TT to a campground near Ridgeway, CO and were making a day trip with just the truck to some high lake that I don't recall.  I pulled over at a nice overlook and when I restarted the truck, the service engine light came on.  I took the truck into Montrose to a Dodge dealer and they told me it was the oxygen sensor.  They didn't have one but they reset the light.  I owned the truck for two more years before it was stolen and the light never came back on,
 
Lowell said:
  I owned the truck for two more years before it was stolen and the light never came back on,
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Lowell, now you have some thief ticked off at you for allowing him to steal a truck with a known possible fault that may endanger his happiness while taking his joyrides. In this day and age, he may even sue you. ;D
 
It is useful to note that "Service Engine Soon" is never an emergency - "soon" can be days or weeks. In newer vehicles, it is often a problem with the emissions control stuff, maybe even just a  loose gas cap.  I'm not suggesting it be ignored, but don't lose your cool if the light comes on.
 
A little philosophy....  The " 'Check engine light" keeps the economy going. Why ?
1. Auto manufactures were forced to add pollution control systems to all autos and trucks.
2. All those gadgets had to be invented and produced..sensors galore; some important some stupid.
examples.. catalytic converters...oxygen sensors..and many more
3. Inventions like OBD1 and OBD2 test equipment.
4. Extra idiot light on the dash that doesn't tell you what is wrong, except to give you anxiety.
5. Extra trips to a mechanic that hopefully tells you what the problem is.
6. Provides a perfect opportunity to him him throw new parts into your auto/RV. How are you going
  to  prove that all were necessary ?
7.  and much more...see if you can add to the list.

  I have an annoying situation which only affects my low idle speed. Happens that the light will come on and disappear a few days later. Some solenoid that controls the air intake to the manifold only at idling.
  estimated repair cost about $300. I have put that out of my mind.
  I miss that little idle adjustment screw on my ancient cars.

As you can see I love to rant about "important stuff".



 
 
Carson: you can get an Idle air control solenoid valve for RockAuto.com for about 1/2 of the local parts stores..Just make sure it is the Original Equpment Manufacturers (OEM) item. usually they aren't hard to replace and the fuel milage improves also!
 
I am wondering how this came out. I would do no maintenance or change anything (except filters) until I had run the second tank with a double dose of seafoam or Brahmans B12 through it. When You get the second tank run the generator at at least 1/2 -3/4 load  for at least one hour to get fresh gas through the carb/fuel system on the generator.You can mark this down as your monthly run on the generator.
Bill
 
Guys, an 02 sensor depending on which one it is could cause severe engine damage, if ignored. A front 02 sensor tells the pcm how much fuel to inject into the engine. Too much and it will wash the cylinder walls and contaminate the oil, too little and it could burn holes in the pistons. I just had one fail on my pickup and it flooded the right side of the engine so bad it wouldn't hardly run. Most of the time a SES light isn't serious, but one never knows for sure.
 
92GA said:
Guys, an 02 sensor depending on which one it is could cause severe engine damage, if ignored. A front 02 sensor tells the pcm how much fuel to inject into the engine. Too much and it will wash the cylinder walls and contaminate the oil, too little and it could burn holes in the pistons. I just had one fail on my pickup and it flooded the right side of the engine so bad it wouldn't hardly run. Most of the time a SES light isn't serious, but one never knows for sure.
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Even if you remove the main 02 sensor, the vehicle should run fine, in most cases,  other than the MIL & poorer MPG. It's unlikely you would notice any other differences in performance. If the 02 sensor is bad, it should be able to use all the other sensors in open loop mode. At least if the O2 sensor problem is detected, and I don't see how it could not be in an OBD2 (after 1997) vehicle.

Was there more than one OBD2 code? What year was the vehicle?

-Don-  Reno, NV
 
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