Thank you for clarifying that for me. And it's a single sensor system. Can you check fuel trim with a scanner by chance?? A friend of mine just bought one.

 

If the truck is 96 it's a minimum of dual o2 sensor system. It will have an o2 post cat, in fact I believe the port is on the end of the cat. Our 95 and older are single sensor.

 

There is one after the first cat. Nothing after the second one lol I think there is one on the front manifold but I didn't think that was relevant.

 

You need a scanner with live data. The first sensor reads the air fuel mixture the one after the cat monitors cat performance. The upstream sensor should always switch rich and lean. Down stream should always be in them middle not switching. You may have three on in each header and one after the cat. A scanner with live data can tell you what each sensor is reading.

 

How do I know which sensor is which?? And I don't believe there's one on the rear manifold but I could be wrong. And what should I be looking for?? A sensor not responding or with no data at all??

 

Your looking for one not responding or responding really slow since those are the codes you have.

 

OK in did a little more research. It looks like you were right with your first codes. The definitions I gave you were for OBDI and your 96 is OBDII. So not s lot of change but if this is correct you should have 3 sensors. One on the left header one on the right and one at the cat. Its the left and right ones we are concerned with. It is still important to verify the problem or we are just wasting time. The sensors should read lean or low voltage if the code is correct. The fuel trim should be high ( lots of fuel added). If trim isn't high you have a fuel problem. If it is high and both sensors are lean then you have an air leak. If the sensors are not moving there is a sensor problem. Being lean on both banks means you have excess air getting into both heads. That means air coming in last the butterfly, IAC, or a leak in the manifold or vacuum lines. It could also be a MAF issue but normally that would set its own code. You can check the MAF with the scanner. To check for sensor response, you can make the mix rich by running propane from a torch into the intake through a vacuum line. It should respond immediately. To make it lean just pull a vacuum line.

 

The MAF is good, I believe I may have vacuum leaks. I'll have to use that scanner to check for sure. And as far as fuel trim goes what is it listed as, and what SHOULD it read. Also you said the sensor readings should fluctuate correct?? I just want to make sure I'm looking for the right things. And thank you.

 

Yes the front 2 O2 sensors should switch between rich and lean. The rear sensor after the cat should stay steady in the middle unless you aired adding gas or air. The O2 sensors read from 0 to 5v. For the fuel trim there is no set number. Ideally it wants to be at zero. It can go from + 10 to -10 ( if I recall correctly). The higher the number the more fuel its adding to the base mixture in the memory. Negative numbers mean the computer is subtracting fuel. If the numbers are high it means the computer is running the injectors at full duty cycle and still can't reach a stable mixture. Usually you are positive 1 or 2 with it switching around a bit. If you clear the memory or pull the negative cable you can watch the fuel trim work to reset the baseline fuel trim starting from the factory default. Our shop cars in school were reset so often they hardly ever learned a good baseline.

 

Thank you. What are the o2 sensors listed as?? If I remember correctly it wasn't so simple as "o2 sensor 1" and "o2 sensor 2"