DTC Advanced Diagnostics: P1157
DTC P1157:Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS Circuit High 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 (sensor 1) transmits a signal to the powertrain control module (PCM). 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 PCM 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 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 PCM 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
Execution
Continuous
Sequence
None
Duration
5 seconds or more
DTC Type
Two drive cycles, MIL on
OBD Status
PASSED/FAILED/NOT COMPLETED (STILL TESTING)

Enable Conditions
Condition
Minimum
Maximum
Engine coolant temperature
[ECT SENSOR 1]
68 °F (20 °C)
–
Battery voltage [BATTERY]
10.5 V
–
State of the engine
Running
No active DTCs set (prevents monitor from running)
P0117, P0118, P0135, P2195, P2238, P2252
Other
At least 18 seconds after applying current to the A/F sensor (sensor 1) heater
[ ]: HDS Parameter

Malfunction Threshold
The A/F sensor (sensor 1) element resistance is 250 ? 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
PCM internal circuit failure

Confirmation Procedure
Operating Condition
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, then let it idle.

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 battery.