DTC Troubleshooting: P0138 (63)

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


1.Turn the ignition switch ON (ll).

2.Do the DTC CLEAR in the CLEAR MENU with the Honda PGM Tester or the HDS.

3.Start the engine. Hold the engine speed at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on, then let it idle.

4.Check the AF FB AVE in the DATA LIST with the Honda PGM Tester or the HDS.

Is the value 1.0 or more?


YES - Go to 5.


NO - Check for poor connections or loose terminals at the  secondary HO2S (Sensor 2) and the  ECM/PCM, then go to 1.


5.Check the HO2S S2 in the DATA LIST with the Honda PGM Tester or the HDS.

Is the voltage stay at 0.75 V or higher?


YES - Go to 8.


NO - Go to 6.


6.Test-drive under the following conditions.
  • Engine coolant temperature more than 70°C (158°F)
  • A/T in D position (M/T in 5th gear)
  • Engine speed at 2,000-3,000 rpm (min-1)
  • Drive about 10 minutes, then decelerate (with the throttle fully closed) for 5 seconds

7.Monitor the OBD STATUS for DTC P0138 in the DTCs MENU with the Honda PGM Tester or the HDS.

Is it FAILED?


YES - Go to 20.


NO - If it is PASSED, intermittent failure, system is OK at this time. If it is EXECUTING, keep the driving condition continually until a result comes on. If it is Out of CONDITION, go to 6 and recheck.


8.Turn the ignition switch OFF.

9.Disconnect the Secondary HO2S (Sensor 2) 4P connector.

10.Connect the Secondary HO2S (Sensor 2) 4P connector terminals No. 1 and No. 2 with a jumper wire.

11.Turn the ignition switch ON (ll).

12.Check the HO2S S2 in the DATA LIST with the Honda PGM Tester or the HDS.

Is the voltage stay at 0.75 V or higher?


YES - Go to 13.


NO - Go to 20.


13.Turn the ignition switch OFF.

14.Jump the SCS line with the PGM Tester or the HDS.

15.Disconnect ECM/PCM connector E (31P).

16.Check for continuity between ECM/PCM connector terminals E4 and E20.

Is there continuity?


YES - Go to 29.


NO - Go to 17.


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

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

19.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 22.


NO - Repair open in the wire between the ECM/PCM (E20) and the secondary HO2S (Sensor 2), then go to 22.


20.Turn the ignition switch OFF.

21.Replace the secondary HO2S (Sensor 2).

22.Turn the ignition switch ON (ll).

23.Do the ECM/PCM RESET in the CLEAR MENU with the Honda PGM Tester or the HDS.

24.Do the ECM/PCM idle learn procedure.

25.Start the engine. Hold the engine speed at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on, then let it idle.

26.Test-drive under the following conditions.
  • Engine coolant temperature more than 70°C (158°F)
  • A/T in D position (M/T in 5th gear)
  • Engine speed at 2,000-3,000 rpm (min-1)
  • Drive about 10 minutes, then decelerate (with the throttle fully closed) for 5 seconds

27.Check for Temporary DTCs or DTCs in the DTCs MENU with the Honda PGM Tester or 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 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC troubleshooting.


NO - Go to 28.


28.Monitor the OBD STATUS for DTC P0138 in the DTCs MENU with the Honda PGM Tester or the HDS.

Is it PASSED?


YES - Troubleshooting is complete.n


NO - If it is FAILED, check for poor connections or loose terminals at the  secondary HO2S (Sensor 2) and the  ECM/PCM, then go to 1. If it is EXECUTING, keep the driving condition continually until a result comes on. If it is Out of CONDITION, go to 25 and recheck.


29.Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM.

30.Start the engine. Hold the engine speed at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on, then let it idle.

31.Test-drive under the following conditions.
  • Engine coolant temperature more than 70°C(158°F)
  • A/T in D position (M/T in 5th gear)
  • Engine speed at 2,000-3,000 rpm (min-1)
  • Drive about 10 minutes, then decelerate (with the throttle fully closed) for 5 seconds

32.Check for Temporary DTCs or DTCs in the DTCs MENU with the Honda PGM Tester or 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 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC troubleshooting.


NO - If the  ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM.n