DTC Troubleshooting: 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, record all freeze data and any on-board snapshot, and review the general troubleshooting information.
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 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
      

1.
Problem verification:

Problem verification
?1.
Press the engine start/stop button to select the ON mode.

?2.
Clear the DTC with the HDS.


?3.
Start the engine. Hold the engine speed at 3,000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle 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.?
2.
Open wire check (VSB1 line (VSB2 line)*):

Open wire check (VSB1 line (VSB2 line)*)
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Jump the SCS line with the HDS.


?3.
Disconnect the following connectors.

?4.
Check for continuity between test points 1 and 2.
Test condition
OFF mode
 
PCM connector C (51P): disconnected
 
A/F sensor (Sensor 1) 8P connector: disconnected
Test circuit
VSB1 (VSB2)*
Test point 1
Rear A/F sensor (Bank 1, Sensor 1) 8P connector No. 8 (LT GRN)
 
Front A/F sensor (Bank 2, Sensor 1) 8P connector No. 8 (WHT)*
Test point 2
PCM connector C (51P) No. 25 (LT GRN)
 
PCM connector C (51P) No. 28 (WHT)*


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), then do the repair verification.
3.
PCM internal circuit check:

PCM internal circuit check
?1.
Exit the SCS mode with the HDS.


?2.
Reconnect PCM connector C (51P).

?3.
Start the engine. Hold the engine speed at 3,000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle 2 minutes.

?4.
Measure the voltage between test points 1 and 2.
Test condition
Engine running
 
A/F sensor (Sensor 1) 8P connector: disconnected
Test circuit
VSB1 (VSB2)*
Test point 1
Rear A/F sensor (Bank 1, Sensor 1) 8P connector No. 8 (LT GRN)
 
Front A/F sensor (Bank 2, Sensor 1) 8P connector No. 8 (WHT)*
Test point 2
Body ground


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, then do the repair verification.
     
NO
     
     
     
The PCM internal circuit is OK. Replace the A/F sensor (Sensor 1), then do the repair verification.
Repair verification (OBD STATUS check):

?1.
Reconnect all connectors.

?2.
Exit the SCS mode with the HDS.


?3.
Press the engine start/stop button to select the ON mode.

?4.
Reset the PCM with the HDS.


?5.
Do the PCM idle learn procedure.

?6.
Monitor the OBD STATUS for DTC P2251 and/or P2254* in the DTCs MENU with the HDS.
DTC Description
OBD STATUS
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
  


Does the HDS indicate PASSED, FAILED, or NOT COMPLETED?

     
PASSED (P2251)
     
     
     
Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting. ?
     
PASSED (P2254)
     
     
     
Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting. ?
     
FAILED (P2251)
     
     
     
Go to step 1 and recheck.
     
FAILED (P2254)
     
     
     
Go to step 1 and recheck.
     
NOT COMPLETED
     
     
     
Keep idling until a result comes on.