DTC P2251, P2254 (19-21 9-Speed A/T)

DTC P2251  : Rear Air Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) VS Circuit High Voltage

DTC P2254  : Front Air Fuel Ratio (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 .
• 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. Turn the vehicle to the OFF (LOCK) mode.

   - 4. Start the engine.

   - 5. 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.

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

   DTC Description	Confirmed DTC	Pending DTC
   P2251 Rear Air Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) VS Circuit High Voltage
   P2254 Front Air Fuel Ratio (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 on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the on-board snapshot - Refer to: How to Troubleshoot the Fuel and Emissions Systems .

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

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

   - 2. Jump the SCS line with the HDS, and wait more than 1 minute.

   - 3. Disconnect the following connectors.

   PCM connector E (80P)

   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 E (80P): disconnected
   	A/F sensor (Sensor 1) 6P connector: disconnected
   Test point 1	Rear A/F sensor (Bank 1, Sensor 1) 6P connector (female terminals) No. 6:
   	Front A/F sensor (Bank 2, Sensor 1) 6P connector (female terminals) No. 6 *:
   Test point 2	PCM connector E (80P) No. 45 - Refer to: PCM Connector for Inputs and Outputs (19-21 9-Speed A/T)
   	PCM connector E (80P) No. 42* - Refer to: PCM Connector for Inputs and Outputs (19-21 9-Speed A/T) .

   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 (E45 (E42) *) and the A/F sensor (Sensor 1).

3. PCM internal circuit check

   - 1. Reconnect the following connector.

   PCM connector E (80P)

   - 2. Exit the SCS mode with the HDS.

   - 3. Start the engine.

   - 4. 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.

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

   Test condition	Engine running
   	A/F sensor (Sensor 1) 6P connector: disconnected
   Test point 1	Rear A/F sensor (Bank 1, Sensor 1) 6P connector (female terminals) No. 6:
   	Front A/F sensor (Bank 2, Sensor 1) 6P connector (female terminals) No. 6 *:
   Test point 2	Body ground

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

   Is there about 0.2 V or less?

   YES 

   Check for any authorized service information related to the DTCs or symptoms you are troubleshooting, or substitute a known-good PCM, then recheck. - Refer to:

   PCM Removal and Installation (19-21 9-Speed A/T)

   If DTC P2251 and/or P2254 goes away and the PCM was substituted, replace the original PCM - Refer to:

   PCM Removal and Installation (19-21 9-Speed A/T) .

   NO 

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