silverfarmer

Just a follow up. I went through all the harness I could get to up to the DME and I found nothing problematic. Checked wiring, checked relay connections, essentially anything I could find/trace in the trunk after removing the covers and wood floor. I re-swapped the 2 post cat sensors back to their original positions. I cleaned and dielectric greased the harness connections and sensor plugs of both. I removed the driver seat and cleaned and dielectric greased the ecu harness connection, nothing appeared faulty with the wiring. I had some nice weather so I went for about a 100 mile drive today (highway, back roads, stop and go, stopped for gas). No CEL, no problems with anything!? Ran like a top. I don't have a lot of hope yet for this "fix", but mileage will tell. It would be nice if it is this simple. Thank you.

Thank you. I'll give it a go! Again, I appreciate your help.

Sorry for lag time, getting over some flu bug finally. I went over all the voltages and resistances and connections again. I visually checked the harness connections back to where they were last accesible. Both sides. Nothing out of the ordinary. Applied a bit of dielectric grease to each pin and reconnected sensors. I erased the P0140 code and went for almost 70 mile drive: back road, highway, stop and go in town traffic. No CEL, left car running and got out to open garage, returned to CEL? Pulled in hooked up Durametric without turning off car. P0140 again. Compared voltages as you suggested pre and post cat each side. While my plots are not as smooth or consistent (with regard to amplitude), but I think they look correct. Pre on both oscillate between 0.05 and 0.75 and post 0.98 and 1.02. Would you suggest investigation further up the harness from where it disappears in the trunk to the direction of the DME? Is there a diagram of the path anywhere? On an aside: The Durametric I have readout for P0140 is cyl 4-6? Is that considered bank 1 or 2? I'm checking both sides, but trying to see if there is a bug\error on my readout. Thanks!

So my results: Engine running: PIN 3 TO PIN 4 ~453mV PIN 3 to GND ~720mV PIN 1 TO PIN 2 never settled, jumped all over on multiple attempts ! So am I looking for a bad ground from the harness to the DME? Engine NOT running: PIN 1 to GND ~6.75kohm PIN 2 to GND ~6.75kohm PIN 3 to GND ~1.13kohm PIN 4 to GND ~52.7kohm Your suggestions appreciated!

Thank you for the quick reply. I really appreciate your expertise and willingness to help. I am headed to the shop right now! Merry Christmas!

I found this from JFP in PA (02/2019): This is a great example of why you shouldn't replace anything before you know what the codes are telling you. P0134 is the code for the interruption of the signal from the O2 sensor ahead of the three way cat on bank #1. Usually, this is caused by a problem with either the signal or ground wire connected to the sensor, and is rarely caused by the sensor itself. The diagnostic tree in the factory OBD II manual for the car involves checking the wiring by using a multimeter to test the ohms between pins #1 and 2 (should read 1.8-2.5 ohms at 20 degrees C), and test the ground continuity between each of these pins and the sensor housing itself (each should read infinite ohms). The harness connector pins 3 and 4 should read ~450 mV, and pin 3 to ground should read ~750 mV. Harness connector pins 1 and 2 should show battery voltage. If any of these tests are out of bounds, you have a wiring fault, not a sensor fault. My questions regard the harness testing. A.) Should the car be running during the test of the harness connector? B.) Am I reading testing PIN 3 TO PIN 4 should read ~450mV? 3.) PIN 3 to ground (any body bolt?) should read ~750mV? 4.) PIN 1 TO PIN 2 should read battery voltage? I did the sensor tests: PIN 1 to PIN 2 read 1.7 ohm (at 12 degree C) and grounding PIN 1 and then PIN 2 read OL on each reading. So I think my sensor and the accompanying wiring is OK. Thanks for the help, lest I fry some electronics!

Thanks for the reply Mike, So am I correct looking for an electrical problem/disruption somewhere from connection point of bank 2 post cat sensor to ECU?

Hi everyone. I have a 1998 stock manual boxster. My car was impacted by a mini-van in the driver's rear quarter. I pick up my repaired car at the collision center and 30 miles (of 120 mile) trip home I get a solid CEL. Car was not giving any indication of a problem, runs fine rest of way home. Hook up durametric and get P0140 O2 sensor behind cat conv cyl (4-6). No other codes. I erase code. Next day I take car out for a drive, 8 miles out another solid CEL. Again, drive home, hook up durametric and get codes P0140, P0160 and P1121. I erase codes. I swap the post cat sensors from side to side and go for a drive. 38 miles no problem, get out of car to open garage door at home, get back in and solid CEL is illuminated. Pull in garage, leave car running and hook up durametric. One code: P0140. So code didn't follow sensor. I then actual value graphed the pre and post cat voltages. I have attached the screen shot. I really could use some help interpreting it and/or suggestions on what path to take from here. Could the cat have suffered internal damage from the accident and need replaced? The post cat sensors seem fine. It is quite variable as to when the CEL appears, I don't begrudge the shop as their test drive after repairs was short according to the mileage out. Nothing was replaced w.r.t. the exhaust system. Repairs were mainly suspension components and cosmetics. I did try posting on another forum, but my post never showed up!? Thanks!