Hey,
My CEL is on - pulling a P0138. What are the chances that it is a short and not the sensor? Is there anyway to test the sensor? Truck seems to run fine... starts hard when cold but once its been ran for a while, it starts right up - related?
Thanks!

 

P0138 1/2 O2S Shorted To Voltage

yes you can test the sensor. The steps are in a search, i think

 

Hard starting cold won't be the O2 sensor. Being that it's a downstrream O2 code makes it more likely there is some damage and/or corrosion on the wires. You definately want to scoot under there and take a look.

Is your hard start when cold a long crank time, a rough idle or a sputter and shut off?

 

Thanks for the replies. A mechanic friend told me that the hard start (long crank time) sounds like a check valve. As for the wires on the O2 sensor, I had a quick look this am and the wires on the sensor seem ok - I didnt try to follow them up the harness... just figured it is a bum sensor. There is one pre-cat and one post-cat.

I filled up Thursday though and every now and then, there is a strong gas smell in and around the truck. The ground is dry underneath it and also I am getting really bad mileage.
Any ideas?

 

bumped

 

If you are getting bad gas mileage then it would have to be bad o2 sensor your computer wouldnt know if it needs to lean out or be rich and when you have a bad sensor they run rich so get new o2's

 

If you were running really rich, that would explain your gas smell and your poor gas mileage. An o2 sensor should be able to tell when you're running rich and should send a signal to correct the pcm. However if that isn't happening, the sensor and/or wiring for it is malfunctioning. Because your trouble code is referring to the post cat sensor on the drivers side, it doesn't really have anything to do with your fuel mixture. My understanding is that it just tells the PCM whether your cat is working appropriately. I am surprised that you're not getting another code indicating running rich.

It is possible that this isn't the case and they are unrelated. If you have a gas leak, it would explain your poor mileage. Gas evaporates after a while so that may be why you aren't noticing it.

 

The truck is new to me (about a month) so still learning. The gas smell is only present every now and then - not consistent. Is 450km consideredbad mpg for my 4.7 quad? It is not giving any other code - and I just have the one sensor post cat. Another issue i noticed... front main seal is leaking - what kind of project is that? I am not afraid to tackle things but when one needs specialty tools and messing with timing... I get nervous. I may need to spend about $1000.00 to clean some of this stuff up... Truck has 182,000km should be still lots of life. Needs a new A/C Compressor - bad clutch. I am beginning to realize why I got it so cheap. Still really like the truck though, just needs some lovin.
Any advice is greatly appreciated.

 

basically, your bad O2 sensor is making your truck run rich. Here is why...

Think about it for a second. It is an O2 sensor. It detects O2. Right? Specifically, it is detecting unburned Oxygen in the exhaust...

The O2 sensor generates a voltage based on the amount of O2 it is sensing. It is comparing your exhaust to the outside air (where there is obviously a whole ton of unburned O2). Now, if your O2 sensor cannot tell the difference between the outside O2 level and the O2 level in the exhaust (because it is bad), the difference between the two readings is 0, which makes the O2 sensor send the lowest voltage to the computer, indicating lean (you have as much O2 in your exhaust as there is in the air basically).

As a result, your computer thinks to itself "Gee, we might want to add a bit more fuel to prevent from burning holes in the pistons." So, more fuel is added to compensate for the lean condition.

Problem is, the O2 sensor was bad, and no matter how much fuel is dumped in, it still reads lean. Obviously, if this process kept up, your injectors would eventually just be squirting gas out the exhaust. The thing would flood and be undriveable. And we don't want that.

So, at some point the computer says "Look, I know that eventually the amount of fuel added will result in all of that Oxygen in the intake being burned. Yet, you, Mr. O2 sensor, insist on telling me there is still no difference between the air outside and the air inside the exhaust. Well, I am not buying it."

So, the computer decides to ignore the O2 sensor. It defaults to some kind of pre-set condition. You get a CEL and the engine runs rich (by design, since rich is better than lean - gas is cheaper than an engine).

Start with the O2 sensor...