Emissions Codes

[Rory O'Brien]

So my Jeep has been throwing P0421 and P0431 since I bought it in July. I know they're pre cat issue codes but i used a MaxiDiag reader tool and from the info gathered on the scanner I can tell you this about it:

Catalyst 1/1 Switch Frequency Ratio
Test Value: 30.03%
Max Limit: 29.25%
Status: Fail

Can anyone tell me what this means?

Also

O2 Sensor 1/2 Lean (Low) Voltage
Test Value: .039V
Max Limit: .313V

O2 Sensor 1/2 Rich (High) Voltage
Test Value: .666V
Min Limit: .607V

I don't know too much about these scanners or what these values tell me.

Basically what I'm looking to find out is if it's worth the shot of changing the upstream O2 sensors before I drop serious money on replacement pre cats. O2 sensors don't come dirt cheap in Canada so if there's no chance it'll help I don't have the money to throw away at them. Any input is appreciated.

 

[Chris]

Those codes mean the O2 sensors are not functioning properly, the catalytic converter is not function properly, or both! So I would start with replacing the O2 sensors (make certain to use the correct NGK sensors, which you can read more about here: The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread), and if that doesn't do it, you need to replace your pre-cats. None of this is anything out of the ordinary, especially with vehicles this age.

 

[Rory O'Brien]

Those codes mean the O2 sensors are not functioning properly, the catalytic converter is not function properly, or both! So I would start with replacing the O2 sensors (make certain to use the correct NGK sensors, which you can read more about here: The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread), and if that doesn't do it, you need to replace your pre-cats. None of this is anything out of the ordinary, especially with vehicles this age.

I've heard the later TJ's with the California cats have been known to fail. Usually around 60-80k miles. I guess I'll start with the upstream sensors and see if it still throws codes. If it still does i'll weld a spaced out bung and see what that does.
Correct me if I'm wrong but from what I understand the upstream sensors effect performance and the downstream sensors give information on cat performance relative to data from upstream sensors.

 

[Chris]

Yes, the later TJs pre-cats tend to fail. It's happened to a lot of us, including myself.

You are right about the sensors. The upstream sensors affect engine performance, while the downstream sensors just provide information. If you had failed upstream sensors it will affect your engine performance, where as the downstream ones won't affect performance at all, but they will give you a pesky check engine light.

 

[Rory O'Brien]

Yes, the later TJs pre-cats tend to fail. It's happened to a lot of us, including myself.

You are right about the sensors. The upstream sensors affect engine performance, while the downstream sensors just provide information. If you had failed upstream sensors it will affect your engine performance, where as the downstream ones won't affect performance at all, but they will give you a pesky check engine light.

Right, and in reference to the O2 sensor post. The 1/1 and 2/1 sensors are actually different units? I figured they would be the same 'model'

 

[Chris]

Right, and in reference to the O2 sensor post. The 1/1 and 2/1 sensors are actually different units? I figured they would be the same 'model'

Nope, believe it or not, they're different models! That's why I compiled that thread, because there was a lot of confusion surrounding the matter. But they are indeed different for the 1/1 and the 2/1 sensors. No idea why that is, but it is what it is.

 

[ohiopatriot]

Nope, believe it or not, they're different models! That's why I compiled that thread, because there was a lot of confusion surrounding the matter. But they are indeed different for the 1/1 and the 2/1 sensors. No idea why that is, but it is what it is.

They are different numbers because the connectors are different so you can not plug B1S1 in B2S1 harness and vice versa, crazy drivability issues arise if that were to happen.

 

[Chris]

They are different numbers because the connectors are different so you can not plug B1S1 in B2S1 harness and vice versa, crazy drivability issues arise if that were to happen.

Ahhh, so the sensor is the same, it's the connector that's different? Makes sense.

 

[KCsTJ]

Just started getting code 31, twice. I know what 31means, I've just not seen a code listed two times .. My exact readout is: 12,31,31,55. Any significance to a code listed twice ??