Quote:
Originally Posted by Clodfobble
It's not the gas cap, man. The code that came up today is the same one as before, failing catalytic converter.
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Now that you have a reader, view the oxygen sensor voltage yourself. As posted long ago, if the O2 sensor is defective, it is reporting a voltage reading that is off on the edge. Intermittent. Therefore the engine computer is intermittently dumping wrong amounts of fuel into the engine. Different gas even from the same station will push that marginal voltage over and back behind a failure line. Obvious when the diagnostic port provides an actual volt number.
Still never answered were answers to tests that would have said so much more. For example, floor it after each restart. Because (and again) some defects are only reported when the accelerator is moved the exact same way after every consecutive restart.
Eventually that defect will become so bad that any mechanic can find it. But this you know because my post was based in provided and known facts. No reasons existed to suspect catalytic converters as defective. Your emission tester only confirmed what was obvious because reasons for that conclusion were also posted.
Engine light and code does not say what is wrong (as others have mistakenly assumed). It only says where to start looking. “Looking”: as in CSI's, "Follow the evidence." Viewing actual numbers - ie voltage from that oxygen sensor. Which is read from the computer by an OBD2 reader (ie Car Chip) attached to the diagnostic port.
What should be obvious to all and is obvious to you - a gas cap has zero relationship to what comes out the exhaust.
Now, did the $2+K mechanic explain the whys as I have done? Welcome to everything in the world. Without reasons why AND numbers, then the guy (any guy) is probably lying. Welcome to history taught by Saddam's WMDs.
Better dealers have a big computer that both reads those numbers AND does the voltage analysis for them (and you). Did the garage that did emission tests use that computer? Or just test emissions with a wand inside the exhaust pipe? Did he provide actual numbers for CO, CO2, NOx etc? Nobody cares if those numbers are good or bad. Only relevant is the actual value and what the manufacturer limits for each were supposed to be.
Whereas the problem could be with other system parts, one likely suspect was one particular oxygen sensor that was not the O2 sensors others were only assuming. Reread those posts to see what your emission test station may have also confirmed.
A diagnostic port is only reporting on what sees symptoms. It does not report what is wrong - as your $2+K mechanic probably has done. Due to marginal operation of a first oxygen sensor, then other following oxygen sensors (after the cat converter) may be reporting symptoms of that defect.
This is only hard if others assume a diagnostic message actually reports a problem. Diagnostic message about the cat converters never said those are defective. Only said what is coming out is incorrect - only reported a symptom. Use the OBD2 to read voltages from that O2 sensor - which is not the one reporting an error. And answer all previous questions including those from last month.