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did a motor swap vq40de direct swap put new upstream cat on driver side as well as o2 sensor put up/downstream cat on passenger side with new upstream o2 sensor. after the swap got a p0420 code bank 1 cleared after i installed those new o2 sensors (^^above) few days later get a weird code p1273 cylinder no.3 high to low side open(bank1)..... literally lost called local mechanic said its a exhaust leak or a vacuum where its sucking to much air. have no exhausts leak that i noticed all head bolts are tight to spec as well


my idea since i only replaced upstream o2 sensors could they be conflicting with each other? went with bosch o2 sensors while the downstreams are still the originals

if anyone has a fail proof way to test for exhaust leaks other then looking for black or putting your hand around the connection points that would be appreciated as well
 

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When you replace the air/flow ratio sensors (front O2 sensors), the ECM can trigger this code if it's self-learning memory is not cleared. Try this first and see if it fixes your problem before getting to deep into it:


1-Start engine and warm it up to normal operating temperature.
2-Turn ignition switch OFF.
3-Disconnect mass air flow sensor harness connector, and restart and run engine for at least 3 seconds at idle speed.
4-Stop engine and reconnect mass air flow sensor harness connector.
5-Make sure Detected Trouble Code (DTC) P0102 is displayed.
6-Erase the DTC memory. (This could be done by disconnecting the car battery for 30-45 min or with a scanner)
7-Make sure no codes are stored in the ECM.
8-Run engine for at least 10 minutes at idle speed.
 
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