Advanced Diagnostics

Advanced Diagnostics - DTC P1157: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS Circuit High Voltage (Engine Type: K24Z7)

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). A heater for the sensor element is embedded in the A/F sensor (sensor 1). When activated, it heats the sensor to stabilize and speed up the detection of oxygen content by controlling current flow through the heater. The current diminishes as the voltage applied to the element reaches a certain range because the amount of oxygen that passes 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 compares the set target air/fuel ratio to the detected air/fuel ratio and adjusts the fuel injection duration. If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM 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 uses air/fuel ratio feedback control to issue a Lean command. If the element is not activated for a set time when power is drawn by 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 A/F sensor (sensor 1) element resistance is 250 Ohms or more for at least 5 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) AFS+ line open
- A/F sensor (sensor 1) AFS- line open
- A/F sensor (sensor 1) failure
- ECM internal circuit failure

Confirmation Procedure

With the HDS
None.

With the Driving Pattern
Start the engine. Hold the engine speed [ENGINE SPEED] at 3,000 rpm without load (in neutral) until the radiator fan comes on, then let it idle.

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 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.