BiZ

I have a 96 Sc400. Last week I had a coil wire go bad that caused the car to run like poo. Luckily it started acting up 3 miles from home. So I limped it home. When I got out of the car I looked underneath and both cats were glowing. After an evening of searching through threads I found the culprit and fixed the coil wire the next day. So now yeserday while driving home from the movies the check engine light comes on. I bought a code scanner and pulled codes P0135 -- P0420 -- P0430 tonight. I searched a few threads and found that the 420/430 codes have to due to an inefficiency in both Catalyst. So I am guessing the the overheating caused this problem. Any input?

And the P0135 is "HO2S Heater Circuit Malfunction, Bank 1 Sensor 1" What exactly is this?

philauldridge

PO135.... there is a heater circuit built into the O2 sensor to insure that the sensor functions properly right after startup. The ECU constantly measures the resistance coming from the heater circuit, and if it sees an inappropriate resistance (i.e., the heater is NOT working), then it throws off that code. Most likely is an indication of a bad O2 sensor. Fortunately, for you, this code does NOT affect driveability at all (well, maybe a bit for the first couple of minutes until the exhaust heats everything up anyway), but, of course, it causes the check engine light to be on continuously, masking other adverse engine conditions that might pop up.

Finally, the aft O2 sensor on each side is only there to insure that the cat is doing its job correctly, by insuring that a properly lean mixture comes through at that point. Again, technically, if you do not have other problems, this condition does NOT affect the driveability of the car, just the quality of emissions you're dumping out the rear.

It's a good possibility that changing that O2 sensor will solve the problem.

I can't be certain on this, but I believe that bank 1 is the driver's side... Check me on this!