I recently changed an oxygen sensor in my Accord

Never do this process.

Why did you replace the o2? What code? Codes never identify bad parts, just failed systems

never clear the codes till the repair is verified, then the code can be cleared. Clearing it does nothing as the issue is still there.

Roy

Here is the flow chart for this code

DTC P0138: Secondary HO2S (Sensor 2) Circuit High Voltage

Turn the ignition switch ON (II).
Clear the DTC with the HDS.
Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
Check the HO2S S2 in the DATA LIST with the HDS.
Does the voltage stay at 0.75 V or higher?

YES - Go to step 7.

NO - Go to step 5.

Test-drive under these conditions:
Engine coolant temperature more than 158 °F (70 °C)
A/T in D (M/T in 4th gear)
Engine speed at 2,000 - 3,000 rpm
Drive about 10 minutes, then decelerate (with the throttle fully closed) for 5 seconds
Monitor the OBD STATUS for DTC P0138 in the DTCs MENU with the HDS.
Does the screen indicate FAILED?

YES - Go to step 19.

NO - If the screen indicates PASSED, intermittent failure, system is OK at this time. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 5 and recheck.

Turn the ignition switch OFF.
Disconnect the Secondary HO2S (Sensor 2) 4P connector.

Connect Secondary HO2S (Sensor 2) 4P connector terminals No. 1 and No. 2 with a jumper wire.
Turn the ignition switch ON (II).
Check the HO2S S2 in the DATA LIST with the HDS.
Does the voltage stay at 0.75 V or higher?

YES - Go to step 12.

NO - Go to step 19.

Turn the ignition switch OFF.
Jump the SCS line with the HDS.
Disconnect ECM/PCM connector E (31P).

Check for continuity between ECM/PCM connector terminals E4 and E20.
Is there continuity?

YES - Go to step 28.

NO - Go to step 16.

Remove the jumper wire from the secondary HO2S (Sensor 2) 4P connector.

Connect secondary HO2S (Sensor 2) 4P connector terminal No. 2 to body ground with a jumper wire.

Check for continuity between ECM/PCM connector terminal E20 and body ground.
Is there continuity?

YES - Repair open in the wire between the ECM/PCM (E4) and the secondary HO2S (Sensor 2), then go to step 21.

NO - Repair open in the wire between the ECM/PCM (E20) and the secondary HO2S (Sensor 2), then go to step 21.

Turn the ignition switch OFF.
Replace the secondary HO2S (Sensor 2).
Turn the ignition switch ON (II).
Reset the ECM/PCM with the HDS.
Do the ECM/PCM idle learn procedure. See: Powertrain Management Computers and Control Systems Engine Control Module Testing and Inspection Programming and Relearning
Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
Test-drive under these conditions:
Engine coolant temperature more than 158 °F (70 °C)
A/T in D (M/T in 4th gear)
Engine speed at 2,000 - 3,000 rpm
Drive about 10 minutes, then decelerate (with the throttle fully closed) for 5 seconds
Check for Temporary DTCs or DTCs with the HDS.
Are any Temporary DTCs or DTCs indicated?

YES - If DTC P0138 is indicated, check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and the ECM/PCM, then go to step 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.

NO - Go to step 27.

Monitor the OBD STATUS for DTC P0138 in the DTCs MENU with the HDS.
Does the screen indicate PASSED?

YES - Troubleshooting is complete.

NO - If the screen indicates FAILED, check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and the ECM/PCM, then go to step 1. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 24 and recheck.

Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM.
Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
Test-drive under these conditions:
Engine coolant temperature more than 158 °F (70 °C)
A/T in D (M/T in 4th gear)
Engine speed at 2,000 - 3,000 rpm
Drive about 10 minutes, then decelerate (with the throttle fully closed) for 5 seconds
Check for Temporary DTCs or DTCs with the HDS.
Are any Temporary DTCs or DTCs indicated?

YES - If DTC P0138 is indicated, check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and the ECM/PCM, then go to step 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.

NO - If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM.
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Dont worry about that now, resolve the code and see if it clears up.

Roy