misfire with P1035 code again, also with code of P0306?

2003 CHEVROLET IMPALA
121,730 MILES • 3.4L • V6 • 2WD • AUTOMATIC
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DAVID CHEN
At mid, of Yun check engine light is on, the GM 213802 up stream O2 Sensor was replaced, the operation back to normal. Last week the Check engine light back on again, DTC Look up with P1035 code again, also with code of P0306 Cylinder 6 Misfire Detected, OBD 2 On-Board monitor test was performed showing all OKs. is it simple as park plug problem ? or something more? Please noted that the timing belt never been changed that causes Problem? Please advice me how to solve this problem seems. Thank you very much with the best regard
Jul 10, 2025 at 5:22 PM
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MECHTRIX
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If you scanned it and it said it was ok than maybe it is ..but i think the 02 sensors gonna be alright since you replaced it alredy ..so id focus on the po306 cylinder 6 missfire ...here a few things to check

1 the number 6 spark plug(if fouled or defective id just replace all of them) ...especially if its been a while .
Ignitiin coil and wires leading to it ...
2..Maf /map sensor

3..Also low compresion in that cylinder and or oil burning can make it miss

4 fualty fuel injectir in that cylinder ..check the wire leading to it
Also if theres a leaky intake at that cylinder it can do it

Most likely and eaiest to check are the the cyl 6 ..plug and the coil
Chances are if you fix that the o2 sensor code wont come back either ..

Good luck .
Jul 10, 2025 at 7:51 PM
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STRAILER
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Well, the first code is the oxygen sensor heater so lets make sure we replaced the correct sensor which I have included in the images below. This will have nothing to do with the misfire. The sensor will be on the right side of the engine.

P1035 - HO2S Heater Performance Bank 1 Sensor 1
P0306 - Cylinder 6 Misfire Detected

The misfire can be the spark plug, wires or coil. Here is a guide to help you see all of the reasons you can have a misfire.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please go over it and get back to us.
Jul 12, 2025 at 8:57 AM
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DAVID CHEN
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Dear Sirs ;Thank you and MECHTRIX very much That the new Ignition coil was installed this morning at 11 AM , The car is operating perfectly, Thank again for your instruction that solve this problem so easily. From David with the best regards
Jul 12, 2025 at 3:45 PM
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MECHTRIX
  • ✓ASE Certified Mechanic
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No worries any time. Kens the best and here is a side note: maybe erase all the old codes and get a fresh start it should be fine now ..but if anything should pop up later down the road always feel free to contact 2carpros were always here to help.
Jul 12, 2025 at 9:29 PM
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