OBD data - interpretation needed

[Radarnyc]

Hi again - my CEL does come on after about 20 minutes. It seems to come one after I go into VTEC range. Can someone take a look at my data and offer some opinions to what they see and what they think the problem is?

DataLog-Jun_01_2024_12-25-29-PM

DataLog-Jun_01_2024_12-25-29-PM Time(s),O2 Bank 2 - Sensor 1 Oxygen Sensor Voltage (V),O2 Bank 2 - Sensor 1 Short Term Fuel Trim (%),Engine Coolant Temperature (°F),Calculated Engine Load Value (%),O2 Bank 2 - Sensor 2 Short Term Fuel Trim (%),O2 Bank 2 - Sensor 2 Oxygen Sensor Voltage (V),Intak...

docs.google.com

Thanks much!

 

[Old Guy]

The log does not make much sense to me. It is reporting a trim for each O2 sensor. The ECU only has a bank 1 and bank 2 fuel trim which does actual fuel control and that is always derived from sensor 1. Sensor 2 is only along for the ride to determine whether the catalytic converter has died. Once the engine is up to temperature, both sensor 1 voltages are swinging from bottom of range to top of range which is normal so the cat inlet sensors appear to be working. Beyond that I find the log kind of useless to look at without having any idea what I am looking for. Kind of like asking a doctor what is wrong; but, unwilling to reveal any symptoms.

I am a metric guy and I have no sense for inHg. Its gotta be kPa or not at all, so in the absence of throttle position and engine RPM I have no real sense for what the engine is doing during the log. This would be a lot easier if you told us what the DTCs were then we would have an idea what we should be looking for. Once you know what the DTC is then you can make a more informed selection about the OBDIII PDI values are that you should log.

 

[Radarnyc]

Thanks for the reply. The code thrown is PO430. I can certainly log other things and take her out again

 

[Old Guy]

P 0430 is a front cylinder bank catalyst failure. This is most likely caused by failure of the front catalytic converter or failure of the secondary O2 sensor (outlet) on the front catalytic converter. The ECU goes into a test routine called an emission monitor to check the operation of the catalytic converter and it is probably after the completion of the test routine (which may take several minutes after start up) that determines the cat failed the test that the CEL comes on. It likely has nothing to do with VTEC operation.

If you have an OBDII scanner that displays data in a real time graphical form there is a test that you can do that involves spraying a short dose of propane into the intake manifold while the engine is running and watching the secondary O2 sensor voltage. The propane gags the engine causing a momentary running rich condition that overloads closed loop control and the cat and should cause the secondary O2 sensor to swing rich. That tells you whether the sensor is / is not dead. If the sensor is not dead then the assumption is that the cat is dead / dying. If you do a Google search you can find videos showing the use of the test to evaluate the condition of the cat and sensors. There are other clues to look for in the O2 sensor voltages that can help you with the diagnosis.

If you don't want to test and diagnose, you can do the Hale Mary and just replace the secondary O2 sensor. If that fixes the problem, great. If it does not fix the problem you probably want to carry out more tests because replacing a catalytic converter is more money and effort that an O2 sensor replacement.

If this is just a catalytic converter / secondary O2 sensor problem, you should not be having any driveability problems. The secondary O2 sensor is just there to monitor the operation of the catalytic converter. It has no engine control function.

Supplying details such as the model year and mileage on the vehicle can be useful details that may help with the diagnosis.