2008 Silverado - alcohol/methanol % sensor

Mossyoakglock · September 2, 2014

Can somebody tell me if my truck has the alcohol/ethanol % sensor?

Truck is a 2008 Silverado 5.3L w/ AFM and NON-FlexFuel. It is the LH6 motor.

newdude · September 2, 2014

Non flex fuel shouldn't have the sensor.

00Silverado4x4 · September 2, 2014

If I recall correctly GM doesn't use a sensor at all anymore. Even in the e85 engines.

Mossyoakglock · September 2, 2014

What does it use to measure ethanol content/octane rating? The O2 sensors?

I'm having a rough start issue in the mornings and we are not sure what it is. No codes and all tests at the dealer are coming back perfect. I was thinking the alcohol sensor might be reading a higher contect that it should be. They did a relearn but it didn't help. They think there is an update for my truck but they can't tell until they get it connected to the system (the tech that is trained to do that was no there on Saturday).

If if is the O2 sensors that detect ethanol/octane contect then should I replace them? I can get all 4 for around $120 (AC Delcos from Rockauto). Could they be going bad but not throwing a code yet?

00Silverado4x4 · September 2, 2014

Yes the computer monitors the air/fuel mixture and if it's calling for a certain amount of fuel above normal it'll flip over to the ethanol charts. So in a sense it's more of a monitoring of the system rather than a sensor.

To answer your question, until you have a code or something more definitive to go by I wouldn't be replacing parts to hopefully fix your truck. Now having said that, if you are higher mileage (100k+) then it probably wouldn't hurt to at least take a look, if not replace, your O2 sensors.

txab · September 2, 2014

http://www.gm-trucks.com/forums/topic/78169-e-85-refueling-events/

Mossyoakglock · September 2, 2014

I've read about the refueling event. Most of it has been about E85 and FlexFuel vehicles but mine is not a flexfuel. Even if it is not a flexfuel vehicle would it still do the fuel relearn procedure since I'm not sure not all gas blends are exactly 10% ethanol?

I will admit that the past few tanks I have filled up and only driven maybe 3-5 miles before shutting it off at home for the night (10+ hours). This past tank (Saturday) I made sure I was as low as possible and filled up with non-ethanol fuel and drove about 10-12 miles after filling up.

Would it be a good idea to run the truck down as low as I can and run another tank of non-ethanol fuel through it to see if it resets itself? Can I disconnect the battery for 10-15 minutes tonight and do a relearn with a fresh, full tank?

It sucks because I've got an intune sitting at the house but I don't want to load anything until I get this issue fixed. If there is a computer update I want to do that before I load the tune and copy the stock tune file.

Mossyoakglock · September 2, 2014

Yes the computer monitors the air/fuel mixture and if it's calling for a certain amount of fuel above normal it'll flip over to the ethanol charts. So in a sense it's more of a monitoring of the system rather than a sensor.

To answer your question, until you have a code or something more definitive to go by I wouldn't be replacing parts to hopefully fix your truck. Now having said that, if you are higher mileage (100k+) then it probably wouldn't hurt to at least take a look, if not replace, your O2 sensors.

I'm almost at 80,000 miles. The problem is that the truck is thrown no codes or anything. All computer tests and fuel pressure test check out good.

The tech at the second dealer did say he can see/feel what I'm talking about (first dealer said they couldn't duplicate the problem) but since there are no codes he's not sure. They were going to do a computer update but the tech hasn't been trained on that yet. He can only do relearns which he did on Saturday.

sdeeter19555 · September 2, 2014

If I recall correctly GM doesn't use a sensor at all anymore. Even in the e85 engines.

Mine appears to...at least I can read it with an Edge Insight.

Mossyoakglock · September 3, 2014

Mine appears to...at least I can read it with an Edge Insight.

Is your truck a flex fuel or not?

sdeeter19555 · September 3, 2014

Flex...that wasn't the question.

Mossyoakglock · September 3, 2014

It must be a Flex-fuel only thing for sure. Everybody that says they have it has a Flex Fuel truck (including everything I could find online).

00Silverado4x4 · September 3, 2014

Mine appears to...at least I can read it with an Edge Insight.

Again, I could be wrong, but there is not a sensor, the reading you're are getting is what the computer is "estimating" your ethanol % to be. To get a better idea read the thread posted above from txab (post #6)

sdeeter19555 · September 3, 2014

Then it does a fairly decent job "estimating" as it fluctuates as you're driving and after fueling.

Mossyoakglock · September 3, 2014

If it uses the O2 sensors to estimate then I wonder if one or more are going bad and giving a false reading but not enough to throw a code. Either way I'm sure they can check the ethanol/alcohol % reading with the Tech II and see how off it is.