Advanced Diagnostics

Advanced Diagnostics - DTC P2252: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS- Circuit Low Voltage






General Description
The air/fuel ratio (A/F) sensor (sensor 1) is installed in the exhaust system and detects oxygen content in the exhaust gas. The A/F sensor transmits a signal to the engine control module (ECM)/powertrain control module (PCM). A heater for the sensor element is embedded in the A/F sensor (sensor 1). It heats the sensor to stabilize and speed up the detection of oxygen content. The increase in current through the heater levels off as the voltage applied to the electrode reaches a certain range because the amount of oxygen that goes through the diffusion layer is limited. The current is proportional to the oxygen content in the exhaust gas, so the air/fuel ratio is detected by the measurement of the current. The ECM/PCM compares the set target air/fuel ratio to the detected air/fuel ratio and controls the fuel injection duration. If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM/PCM uses air/fuel ratio feedback control to issue a Rich command. If the A/F sensor (sensor 1) voltage is high, the air/fuel ratio is rich, and the ECM/PCM uses air/fuel ratio feedback control to issue a Lean command. If the element is not activated or the ECM/PCM terminal voltage is a set value for a set time when power is applied to the A/F sensor (sensor 1) heater, a malfunction is detected and a DTC is stored.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status






Enable Conditions






Malfunction Threshold
The AFS- terminal voltage is 0.40 V or less for at least 4 seconds.

Driving Pattern
1. 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.
2. Let the engine idle for 2 minutes.

Diagnosis Details

Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the ECM/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 battery.