baddbird99

Hey guys its been awhile since I've been on, I'm havin some codes I need some input on. First off its a 99 ls1 trans am ms6, patriot stage II heads, howard cam, injectors, fast 92 mm intake and tb, hooker headers, exhaust, mild set up. I have a tune from frost which has seemed to work excellent. I have not dyno tuned it yet. I recently started getting a very persistent p0135 which is o2 heater circuit malfunction bank 1 sensor 1, I replaced that sensor and it still comes back. Also just started seeing a p0300 which is multiple/random cylinder misfire. I do not have cats and I had frost tune out the back o2 sensors. I checked all plugs and wires everything is getting spark and it is running fine, I'm not sure where to look from there. My next thought was possibly a bad coil pack or harness, but I figured I'd get some more advice before I started throwin money at it. Its ran great for a couple years only seeing the track once and the outside of the barn on a select few weekends. So the mods have been done awhile back but haven't seen a lot of miles. Any help is appreciated. Thanks guys!

rjparth

Just a WAG, but wondering if the factory wiring is damaged on that O2 sensor. Maybe the heater is not working, but ultimately the ECU enters closed loop due to EGT. Later as you drive the signal gets interrupted between O2 and ECU. Again, just a guess.

baddbird99

I will check it out tomorrow, will the o2 still function properly if the heater is not working? Also where would that be at? I was under the assumption the sensor had the element inside of it. My first obdII build I'm not educated on all of the details yet!

rjparth

My understanding is that 12v is applied to the O2's heater via the ignition switch and the computer switches ground as needed for operation upon startup. The heater's job is to get that sensor to operating temp (roughly 600*) faster than allowing it to heat up strictly from exhaust gas. Regardless, the sensor can't help but apply a varying voltage of 0-1 volt based on AFR if it's working properly. Since you replaced it I assume it is working. If your heater wiring was broken and your signal wiring intermittent I think it's one possible explanation of these two codes. You heat up from exhaust gas alone, throw a heater code, switch to closed loop, computer loses signal from O2 at some point, throw a general misfire code. Your misfire code is 0300 too, non cylinder specific, which seems to support the theory.

I'd inspect the factory wiring near the exhaust system for signs of melting damage and overall for critter damage. Then check for voltage on the heater circuit by disconnecting the O2, putting a meter on the harness and turning the key to on. You'd just need to determine which wire is which ahead of time.

baddbird99

Great thanks, so its pretty much narrowed down to the wiring for the o2 sensor, the random missfire had me concerned. I have heard of this code being thrown due to a cracked head, worst case scenario ofcourse, but I think a cracked head would be easier to detect. I will find a scamatic on the wiring and see which one is which. With ignition on I should have 12 volts to the o2 sensor correct?

rjparth

I believe so, but I'll have mine in the air at some point this weekend and can tell you what I have. I'm on my phone, but this might be useful: https://ls1tech.com/forums/generation-iii-external-engine/1311781-oxygen-sensor-wiring-diagram.html