P0420 on 2003 Targa

Hey everybody, I was hoping to get some help with this CEL and trouble code that popped up recently on my 2003 Targa - P0420: Catalyst system efficiency below threshold (Bank 1). I've gathered data using a Bluetooth OBDII adapter and Torque software, and posted it below. It seems TID:$01 CID:$05 is failing (Rich to Lean sensor threshold voltage(constant); Max: 115; Test result value: 131; FAIL), but does anyone know which sensor TID:$01 CID:$05 is referring to? I tend to believe it's the post-cat sensor on bank 1. There's also a rattle coming from the rear of the car, leading me to believe the cats may have some loose honeycomb inside them (at least the cat on bank 1), but I'm hoping the noise is coming from just a loose heat shield or something, and that the P0420 fault is caused by just the oxygen sensor. I've tried to attach screenshots of the test data and the sensor logs in addition to the Mode $06 report below, but encountered an error stating that the images were not actually images, and the Excel file containing the sensor logs was not a valid file. Any help would be greatly appreciated. Thanks, Lorin Mode $06 report generated by Torque for Android ================================================ Vehicle VIN: WP0BA29983S635320 Vehicle Manufacturer: Unknown Vehicle Calibration ID: 0000099661866017 Unit and scaling information are not supplied with the data from the ECU for this type of vehicle. Consulting the manufacturers service book for this information is recommended. Test report: ------------------ TID:$01 CID:$05 - Rich to Lean sensor threshold voltage(constant) Max: 115 Test result value: 131 FAIL ---- TID:$01 CID:$06 - Rich to Lean sensor threshold voltage(constant) Max: 115 Test result value: 52 PASS ---- TID:$03 CID:$01 - Low sensor Voltage for switch time calculation Min: 32 Test result value: 128 PASS ---- TID:$03 CID:$04 - Low sensor Voltage for switch time calculation Min: 32 Test result value: 128 PASS ---- TID:$05 CID:$0c - Rich to Lean sensor switch time(calculated) Max: 320 Test result value: 29 PASS ---- TID:$09 CID:$0a - Time between sensor transitions(calculated) Min: 148 Test result value: 182 PASS ---- End of report.

Very simple. Check pre-cat and post-cat O2 sensors reading on bank 1 when engine is idling fully warmed up. Pre-cat should swing between ~0.2v to ~0.8v almost once a second. Post-cat should be ~0.7v more or less constant. If post-cat mimics pre-cat reading, you cat is shot. If the precat sensor is not switching at fast or not touching the low and high, you sensor is shot.

Also, if you suspect internal damage to the cat, just hit it with a rubber hammer lightly to see if you can hear the same rattle. However, not hearing it does NOT mean the cat is good though. Could be just not hittnig it hard enough...

Thanks, Ahsai! It most definitely is the cat that's at fault - I replaced the post-cat sensor anyway since it was almost dead, but I can definitely hear a rattle in the cat. I plan on replacing the cats with a fabspeed x-pipe with high-flows, then finding a shop to tune the car. Any idea if fabspeed would provide software maps with their hardware?

For P0420 (and P0430) the Porsche reference says to if any other codes for O2 sensor aging are present to replace the indicated sensors then clear the codes and road test the car. If the P0420 error comes back to replace the converter. It does read like the converter brick has come loose and shifted out of position some and this is leading to its reduced efficiency. My 02 Boxster has a P0430 show up every once in awhile. I think the brick is loose as I hear some faint rattle from the exhaust system area. Also, I note the other converter does not, has not ever, generated a P0420 error so I suspect a mechanical failure rather than just a wearing out of the catalyst metals is the problem. Anyhow, I have managed to nurse this along for some years now. I have switched back to a top tier gasoline -- Shell mostly (mainly because there is a handy station and its prices are competitive). I found running discount gasolines had the CEL on with the P0430 error code present much more frequently than when I switched to and stayed with a top tier gasoline. And I try to avoid short trips especially in colder weather. In the summer months the CEL stays dark for months at a time even with shorter trips but in colder weather it comes on every so often. Can't help you regarding the exhaust system questions. I do know the replace converter is expensive. I was quoted around $1000 for the hardware and several hundred dollars for labor to replace it. I live in CA so aftermarket exhaust systems are limited and I have not bothered to research into any that might work here. As long as I can get the car through smog checks every 2 years and the light doesn't come on often enough to be a bother I'm not going to worry about it.

Macster you got lucky. Gas brand didn't matter. I had to repalce the bank 1 cat. The light would come on within 100mi. after a reset (disconnected battery). I swapped the O2's side to side, first the rears, then the forward ones, and kept getting the same code. Being in CA were are screwed as the only legal part is the Porsche part. $1,700 from Sunset Porsche in Oregon was the best price I could find for all the parts at the time.