P0305 code with stabilitrac light

maxfli11 · March 19, 2023

I've read several posts on different forums about this issue, but my sons 2014 sierra 1500, 5.3 is giving that code, and the Stabilitrac light comes on with it. Now get this. We took the air plenum off so we could inspect the throttle body, and when we cranked it up, with the plenum off, the code is gone and the miss is either gone or not nearly as noticeable. Can't smell raw gas anymore. Got mass air flow codes and several others but not the misfire code. Stabilitrac light is gone. Drove it a couple miles and it never threw that misfire code again. Put the plenum back on and it's back to P0305 and stabilitrac light. There are a lot of threads on this and most have resulted in replacing the throttle body, some times the TPS. What in the world is going on to make just #5 misfire? We replaced all the plug wires and the plugs, so that is ruled out. It needed it anyway. At idle the TPS is reading about 20%. Is that what it should be?

silveradosid · March 19, 2023

the ecm detects a miss fire in various ways. one is it gets a signal maf sensor to know how much air is going into the engine and the O2 sensors detect how much is going out . the ecm detected that cyl 5 was below its efficiency. when you took the air plenum off the ecm didnt know what the air volume was

CamGTP · March 20, 2023

I am confused a bit here.

The Plenum is the intake manifold, intake manifolds are plenums. So how did it run with it off?

You must be talking about the intake tubing itself and not the actual intake plenum. Running without the tubing attached would put it into speed density because it can't read the airflow across the MAF sensor. Possible you have a bad MAF sensor.

And yes 20% throttle at idle is normal, it's drive by wire and the throttle blade controls idle.

Edited March 20, 2023 by CamGTP

Homewrecker007 · March 20, 2023

20 hours ago, maxfli11 said:

There are a lot of threads on this and most have resulted in replacing the throttle body

If you do go this route I recommend getting your throttle body rebuilt buy these guys. Pretty much life changing.

https://www.solerengineering.com/generalmotors

maxfli11 · April 3, 2023

On 3/19/2023 at 10:53 PM, CamGTP said:

I am confused a bit here.

The Plenum is the intake manifold, intake manifolds are plenums. So how did it run with it off?

You must be talking about the intake tubing itself and not the actual intake plenum. Running without the tubing attached would put it into speed density because it can't read the airflow across the MAF sensor. Possible you have a bad MAF sensor.

And yes 20% throttle at idle is normal, it's drive by wire and the throttle blade controls idle.

I'm calling it the plenum. It's the large plastic piece that clamps directly to the throttle body. It's between the throttle body and the and the breather and hose. Found out it was the coil pack on #5. Did get MAF sensor faults along with half dozen others but it did run.