Got PO300 code

[latvius]

Was driving home on the highway and horsepower started going downhill. Had to pull over, it will idle fine no problem the moment I try to give it gas it starts to stall. I previously had the o2 sensor error code but haven't changed them yet. I had it towed home last night and I'm going to try and start it up again today to see how it acts.

 

[Tonyrodz]

How's your fuel mileage been? How many miles on it? Could possibly be catalytic converter related.

 

[OR VietVet]

So many things that it could be. So, you had/have oxygen sensor codes but did not address that and now, like @Tonyrodz said, you may have catalytic converter problems along with it. Did you feel a loss of power or a misfire or both? You said you had P0300 code.

 

[latvius]

205000 miles or so. It starts up fine and revs fine this morning, I did some research and yeah one thing was catalytic converters clogged.
Haven't noticed gas mileage problems. To the other question about loss of power, yes that what was started it. I had horsepower loss which led me to pull over. I got the PO300 code when I started reving the engine where it would start to stall out.

 

[latvius]

I ordered a new CAI filter and catalytic converters. The filter is pretty old so why not and after 200k I am sure the converters are due. Will also install all new o2 sensors

 

[nonickatall]

Just measure your O2 Sensor. Its easy.

There are normally two white cables, between them you need to measure the resistance. It should be 5-7 Ohm.
And there should be a grey and a black wire. This are the sensor wires. If your engine is running and warm, you should measure between these lines 1-1.5 Volt.

I'm not sure if your car already has 2 o2 Sensor before cat and behind cat. If, than this two oxygen Sensors check the system. Then you should have in your error code a cat error, if your cat is clocked or not working good, but not an O2 sensor error.

It is very likely that you o2 sensor is the problem, but as I wrote, it's very easy to measure.

 

[Tonyrodz]

Just measure your O2 Sensor. Its easy.

There are normally two white cables, between them you need to measure the resistance. It should be five 6-7 KOhm.
And there should be a grey and a black wire. Tis are the sensor wires. If your engine is running and warm, you should measure between these lines 1-1.5 Volt.

I'm not sure if your car already has 2 o2 Sensor before cat and behind cat. If, than this two oxygen Sensors check the system. Then you should have in your error code a cat error, if your cut is clocked or not working good, not an O2 sensor error.

It is very likely that you o2 sensor is the problem, but as I wrote, it's very easy to measure.

Wouldn't he get an o2 sensor code?

 

[nonickatall]

Wouldn't he get an o2 sensor code?

I don't know how GM that made that on the gmt800but I know from several German car brands, when they have to o2 Sensors, one before the cat and the other behind, the reason is, to measure the difference between this two sensors, to detect, if the cat element is working. So if there is a specific difference between these sensors, you receive no error.

If both o2 Sensors are working and the difference is equal, means the cat element don't change the exhaust gas at all, than you receive a explicit "cat error". That should as well be when the cat clogged and combustion is not that good because of the left exhaust Gas... That should also make and explizit "cat error" or no error.

But if one o2 sensor is electrically defekt, like the heating line has a shortcut, than you receive an explizit o2 sensor error.

I recall that I said, that I don't know how GM that made, but when they have two oxygen sensors, than they do that for the same reason and should handel it in the same way.

 

[rockola1971]

I don't know how GM that made that on the gmt800but I know from several German car brands, when they have to o2 Sensors, one before the cat and the other behind, the reason is, to measure the difference between this two sensors, to detect, if the cat element is working. So if there is a specific difference between these sensors, you receive no error.

If both o2 Sensors are working and the difference is equal, means the cat element don't change the exhaust gas at all, than you receive a explicit "cat error". That should as well be when the cat clogged and combustion is not that good because of the left exhaust Gas... That should also make and explizit "cat error" or no error.

But if one o2 sensor is electrically defekt, like the heating line has a shortcut, than you receive an explizit o2 sensor error.

I recall that I said, that I don't know how GM that made, but when they have two oxygen sensors, than they do that for the same reason and should handel it in the same way.

They do have 4 O2 sensors. 2 post and 2 Pre cat. There are multiple codes with different P numbers for 02 related problems and problems that cause sensor to hi/low limits of rich and lean. Ill concentrate on the codes that relate directly to 02 sensor defects. no sensor output or heating element open on sensor and/or no voltage to heater element. 02 sensor has to be real hot to give valid readings and that is what its internal heating element is for. If the cat(s) were bad I would expect to see a code for a bad cat and that code is generated by using the values of the pre and post cat oxygen sensor readings. There will be a substantial difference in readings between the 2 with a bad cat this in between them. Ive got 2 K chassis (Denali and Tahoe) very close to 300k miles and original cats. Sounds like OP jumped the gun buying cats and that was an expensive mistake.

 

[nonickatall]

Ive got 2 K chassis (Denali and Tahoe) very close to 300k miles and original cats. Sounds like OP jumped the gun buying cats and that was an expensive mistake.

My english is not so good, but as I understand, you think that i'm right.

We in Germany would say:
"Er schoss mit Kanonen auf Spatzen"
What means free translated:
"He shot sparrows with cannons"

 

[Mudsport96]

They do have 4 O2 sensors. 2 post and 2 Pre cat. There are multiple codes with different P numbers for 02 related problems and problems that cause sensor to hi/low limits of rich and lean. Ill concentrate on the codes that relate directly to 02 sensor defects. no sensor output or heating element open on sensor and/or no voltage to heater element. 02 sensor has to be real hot to give valid readings and that is what its internal heating element is for. If the cat(s) were bad I would expect to see a code for a bad cat and that code is generated by using the values of the pre and post cat oxygen sensor readings. There will be a substantial difference in readings between the 2 with a bad cat this in between them. Ive got 2 K chassis (Denali and Tahoe) very close to 300k miles and original cats. Sounds like OP jumped the gun buying cats and that was an expensive mistake.

Over 400k on the original cats here. But always maintained so they are good. Perhaps the OP had another issue that killed cats and may happen again. Or, his crank sensor is flaky and is okay at idle but bad above that. Hopefully, he gets back to us after the parts replacement.

 

[Mudsport96]

My english is not so good, but as I understand, you think that i'm right.

We in Germany would say:
"Er schoss mit Kanonen auf Spatzen"
What means free translated:
"He shot sparrows with cannons"

I love this saying.

 

[latvius]

Replaced converters, sensors and CAI filter, runs fine.

 

[03yukXL]

For what it’s with my 2003 had the same code and issue. Ended up being a failed intake gasket. They get old and harden, then lean air causing a leak condition

 

[latvius]

For what it’s with my 2003 had the same code and issue. Ended up being a failed intake gasket. They get old and harden, then lean air causing a leak condition

So one day you lost power driving then the next day it worked fine?

 

[03yukXL]

Not entirely sure because when it happened I limped it to a safe spot and got it fixed. Didn’t wait for it to come back