DTC Advanced Diagnostics: P2251
DTC P2251:Air/Fuel Ratio (A/F) Sensor (Sensor 1) VS Circuit High Voltage

General Description
USA and Canada models

Mexico models

The air/fuel ratio (A/F) sensor (sensor 1) is installed in the exhaust manifold and detects oxygen content in the exhaust gas. The A/F sensor (sensor 1) transmits a signal to the powertrain control module (PCM), and the PCM controls fuel injection duration by comparing the target air/fuel ratio with the A/F sensor (sensor 1) signal. When the VS voltage is a specified value for a set time, the PCM detects a malfunction and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type
Execution
Continuous
Sequence
None
Duration
38 seconds or more
DTC Type
Two drive cycles, MIL on

Enable Conditions
Condition
Minimum
Maximum
12 volt battery voltage [BATTERY]
9.0 V
–
State of the engine
Running
[ ]: HDS Parameter

Malfunction Threshold
The VS terminal voltage is 3.7 V or more for at least 38 seconds.

Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
A/F sensor (sensor 1) failure
A/F sensor (sensor 1) VS line open
PCM internal circuit failure

Confirmation Procedure
Operating Condition
1.
Start the engine. Hold the engine speed [ENGINE SPEED] at 3,000 rpm without load (CVT in P or N, M/T in neutral) until the radiator fan comes on.
2.
Let the engine idle for at least 2 minutes.
With the HDS
None.

Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data are stored.

Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the 12 volt battery.