What this code means
P1157 may mean the PCM is seeing a possible malfunction in the air fuel sensor 1 AFS circuit.
What the vehicle may do
- The check engine light may be on.
- The vehicle may run normally while the fault is stored.
- The vehicle can have possible fuel control or drivability symptoms if the fault is active.
Possible fault areas
- A/F sensor sensor 1 circuit wiring may be involved.
- Connector or terminal condition may be involved.
- The A/F sensor sensor 1 may be involved.
- PCM software or PCM-related issues may be involved.
Diagnostic path
Open and basic context
On this 2010 to 2015 Honda Civic with the 1.8 gas engine, P1157 points to a problem in the air fuel sensor 1 AFS circuit. In plain terms, the PCM may not be seeing the sensor circuit respond the way it expects. The car may have the check engine light on, and it can run normally or show possible fuel control or drivability symptoms depending on when the fault is active. The broad areas to keep in mind are the A/F sensor circuit wiring, connector and terminal condition, the sensor itself, and possible PCM software or PCM-related issues. Before getting into the pinpoint checks, start with the basic system checks and general troubleshooting basics so you are not chasing a circuit code with a power, ground, connector, or scan-tool setup problem still in play.
Verify the fault first
Start by verifying the complaint with the HDS. Turn the ignition switch to ON (II), or use the engine start/stop button to select ON mode. Clear the DTC, start the engine, wait 1 minute, and then check for pending or confirmed DTCs with the HDS. If P1157 comes back, the fault is duplicated and you move into the circuit checks. If it does not come back, treat it as intermittent for now. At that point, the system is OK at this time, so check for poor connections or loose terminals at the A/F sensor sensor 1, the PGM-FI subrelay, and the PCM. If captured data for this code is available, try to reproduce the same operating conditions instead of guessing.
Check the AFS+ wire for an open
If the code is duplicated, turn the ignition switch to LOCK (0), or select OFF mode with the engine start/stop button. Jump the SCS line with the HDS. Disconnect the A/F sensor sensor 1 4P connector and PCM connector B, 51P. Now check continuity on the AFS+ circuit between PCM connector B, 51P, terminal No. 43, RED wire, and A/F sensor sensor 1 4P connector terminal No. 1, RED wire. If there is continuity, the AFS+ wire is OK and you continue to the AFS- side. If there is no continuity, repair the open in the AFS+ wire between PCM B43 and the A/F sensor sensor 1.
Check the AFS- wire for an open
Next, with the same connectors still disconnected and the ignition still in LOCK (0) or OFF mode, check continuity on the AFS- circuit. Measure between PCM connector B, 51P, terminal No. 42, RED/YEL wire, and A/F sensor sensor 1 4P connector terminal No. 2, RED/YEL wire. If there is continuity, the AFS- wire is OK and the next check is sensor substitution. If there is no continuity, repair the open in the AFS- wire between PCM B42 and the A/F sensor sensor 1.
Substitute a known-good A/F sensor
Once both AFS circuit continuity checks pass, substitute a known-good A/F sensor sensor 1. Reconnect all connectors, turn the ignition switch to ON (II), or select ON mode, reset the PCM with the HDS, and do the PCM idle learn procedure. Then check again for pending or confirmed DTCs with the HDS. If P1157 is still indicated with the known-good sensor installed, the A/F sensor sensor 1 is considered OK. From there, update the PCM if it does not have the latest software, or substitute a known-good PCM. If the code goes away after the PCM update, troubleshooting is complete. If it goes away with a known-good PCM substituted, replace the original PCM. If P1157 is not indicated after substituting the known-good A/F sensor, replace A/F sensor sensor 1.
Repair verification and takeaway
Keep the verification separate from the circuit testing. After the repair path is completed, verify the repair and confirm the code stays gone under the conditions that originally brought it back. The key on P1157 is not to jump straight to the sensor. First confirm the fault, then prove the AFS+ and AFS- circuits, then use the known-good sensor result to separate a sensor issue from a PCM software or PCM-related path. For more diagnostic training, visit stepdiagnostics.com.
Final check
Confirm the fault first, prove the AFS+ and AFS- wiring, then use the known-good sensor result to decide whether the path stays with the sensor or moves toward PCM software or PCM checks.
For more guided automotive diagnostics, visit STEP Diagnostics.
