DTC P2251, P2254

DTC P2251  : Rear A/F Sensor (Bank 1, Sensor 1) VS Circuit High Voltage DTC P2254  : Front A/F Sensor (Bank 2, Sensor 1) VS Circuit High Voltage

NOTE: Before you troubleshoot, review the general troubleshooting information - Refer to: How to Troubleshoot the Fuel and Emissions Systems, or How to Troubleshoot the A/T System (2014 2015), or How to Troubleshoot the Brake Booster Pressure Monitoring System (2016 2017 2018 2019 2020), or How to Troubleshoot the Fuel and Emissions Systems(With Auto Idle Stop System) (2016) .
• If DTC P2251 and/or P2254* is stored at the same time as DTC P0134 and/or P0154*, troubleshoot DTC P2251 and/or P2254* first, then recheck for P0134 and/or P0154*.
• Information marked with an asterisk (*) applies to the front bank (Bank 2).

DTC (PGM-FI)

1. Problem verification

   -1. Turn the vehicle to the ON mode.

   - 2. Clear the DTC with the HDS.

   - 3. Start the engine. Hold the engine speed at 3, 000 rpm without load (in P or N) until the radiator fan comes on, then let it idle for 2 minutes.

   - 4. Check for Pending or Confirmed DTCs with the HDS.

   DTC Description	Confirmed DTC	Pending DTC	Freeze Frame
   P2251 Rear A/F Sensor (Bank 1, Sensor 1) VS Circuit High Voltage
   P2254 Front A/F Sensor (Bank 2, Sensor 1) VS Circuit High Voltage

   Is DTC P2251 and/or P2254 * indicated?

   YES 

   The failure is duplicated. Go to step 2.

   NO 

   Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the A/F sensor (Sensor 1) and the PCM. If the freeze data/on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the freeze data/on-board snapshot.

2. Open wire check (VSB1 (VSB2) * line):

   - 1.Turn the vehicle to the OFF (LOCK) mode.

   - 2. Jump the SCS line with the HDS.

   - 3. Disconnect the following connectors.

   PCM connector C (51P) - Refer to: How to Troubleshoot the Brake Booster Pressure Monitoring System (2016 2017 2018 2019 2020), or How to Troubleshoot the Fuel and Emissions Systems(With Auto Idle Stop System) (2016), or How to Troubleshoot the Fuel and Emissions Systems, or How to Troubleshoot the A/T System (2014 2015)

   A/F sensor (Sensor 1) 6P connector

   - 4. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	PCM connector C (51P): disconnected
   	A/F sensor (Sensor 1) 6P connector: disconnected
   Test circuit	VSB1 (VSB2) *
   Test point 1	Rear A/F sensor (Bank 1, Sensor 1) 6P connector No. 6 (LT GRN)
   	Front A/F sensor (Bank 2, Sensor 1) 6P connector No. 6 (WHT) *
   Test point 2	PCM connector C (51P) No. 25 (LT GRN)
   	PCM connector C (51P) No. 28 (WHT) *

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The VSB1 (VSB2) * wire is OK. Go to step 3.

   NO 

   Repair an open in the VSB1 (VSB2) * wire between the PCM (C25 (C28) *) and the A/F sensor (Sensor 1).

3. PCM internal circuit check

   -1. Reconnect the following connector.

   PCM connector C (51P) - Refer to: How to Troubleshoot the Brake Booster Pressure Monitoring System (2016 2017 2018 2019 2020), or How to Troubleshoot the Fuel and Emissions Systems(With Auto Idle Stop System) (2016), or How to Troubleshoot the A/T System (2014 2015), or How to Troubleshoot the Fuel and Emissions Systems

   - 2. Exit the SCS mode with the HDS.

   - 3. Start the engine. Hold the engine speed at 3, 000 rpm without load (in P or N) until the radiator fan comes on, then let it idle for 2 minutes.

   - 4. Measure the voltage between test points 1 and 2.

   Test condition	Engine running
   	A/F sensor (Sensor 1) 6P connector: disconnected
   Test circuit	VSB1 (VSB2) *
   Test point 1	Rear A/F sensor (Bank 1, Sensor 1) 6P connector No. 6 (LT GRN)
   	Front A/F sensor (Bank 2, Sensor 1) 6P connector No. 6 (WHT) *
   Test point 2	Body ground

   Courtesy of HONDA, U.S.A., INC.

   Is there about 0.2 V or less?

   YES 

   Update the PCM if it does not have the latest software, or substitute a known-good PCM - Refer to: PCM Removal and Installation (2014 2015), or PCM Removal and Installation (2016) ..

   NO 

   The PCM internal circuit is OK. Replace the A/F sensor (Sensor 1) .