A worn or contaminated primary oxygen sensor that has become sluggish with age.; Exhaust leaks upstream of the sensor, allowing outside air to dilute the sample and slow the signal.; Oil or coolant contamination from internal engine leaks fouling the sensor element.; A faulty sensor heater circuit causing the sensor to stay cold and respond slowly.; Wiring damage or poor connections between the sensor and the PCM that add resistance to the signal.; An exhaust restriction or a failing catalytic converter that alters the exhaust pulse seen by the sensor.; Use of leaded fuel or improper sealants that poison the sensor over time.

DTC codes / Honda codes / P1165

P1165 · HondaHO2S11 Slow Response Bank 1 Sensor 1

Q: What does code P1165 mean?

HO2S11 Slow Response Bank 1 Sensor 1. P1165 on Honda vehicles means the powertrain control module has detected that the primary heated oxygen sensor for bank 1 (HO2S11) is responding too slowly to changes in exhaust oxygen content. The sensor's voltage signal is not switching between rich and lean as quickly as the computer expects during its internal rationality test, which can affect fuel trim and emissions.

P1165 on Honda vehicles means the powertrain control module has detected that the primary heated oxygen sensor for bank 1 (HO2S11) is responding too slowly to changes in exhaust oxygen content. The sensor's voltage signal is not switching between rich and lean as quickly as the computer expects during its internal rationality test, which can affect fuel trim and emissions.

SystemPowertrain

Code typeHonda specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
A slight decrease in fuel economy as the engine runs richer or leaner than optimal.
Occasional rough idle or hesitation during acceleration if the slow response affects fuel delivery.
Failed emissions inspection due to increased tailpipe emissions or an incomplete oxygen sensor monitor.
In rare cases, a subtle surging or uneven power delivery under light throttle.

Common causes, most likely first

A worn or contaminated primary oxygen sensor that has become sluggish with age.
Exhaust leaks upstream of the sensor, allowing outside air to dilute the sample and slow the signal.
Oil or coolant contamination from internal engine leaks fouling the sensor element.
A faulty sensor heater circuit causing the sensor to stay cold and respond slowly.
Wiring damage or poor connections between the sensor and the PCM that add resistance to the signal.
An exhaust restriction or a failing catalytic converter that alters the exhaust pulse seen by the sensor.
Use of leaded fuel or improper sealants that poison the sensor over time.

How to diagnose and fix it

Inspect the sensor wiring and connector for corrosion, chafing, or loose pins, and repair as needed.
Check for exhaust leaks between the cylinder head and the sensor using a smoke test or by listening for ticking.
Verify the sensor heater circuit with a multimeter: measure resistance across the heater element and check for power and ground at the connector.
Use a scan tool to view live HO2S11 voltage and confirm slow switching; compare with a known-good sensor or the downstream sensor.
If the sensor is original and high-mileage, replace the HO2S11 with a quality OEM or equivalent sensor after ruling out leaks and wiring.
Clear the code and perform a road test to complete the oxygen sensor monitor and confirm the repair.
If the code returns, check fuel pressure and injector balance, as rich or lean conditions can mimic a slow sensor.

What a slow oxygen sensor really tells you

A P1165 is often set by a lazy sensor that still works well enough to avoid a heater circuit code, so live data graphing is more revealing than a simple resistance check.
Exhaust leaks and vacuum leaks are commonly missed causes because they create a slow or erratic signal that looks like a bad sensor but will not be fixed by replacement.
On many Hondas, the primary oxygen sensor is also used for fuel trim control, so a slow sensor can cause subtle driveability issues that do not always trigger a misfire code.
Replacing the sensor without checking the heater circuit can lead to a repeat failure if the heater is weak but not yet failed completely.
A contaminated sensor from coolant or oil burning may respond slowly without setting a heater code, so inspect the old sensor tip for deposits before condemning it.

Can I keep driving with P1165?

You can usually continue driving with P1165, but avoid long periods of aggressive acceleration or heavy loads until it is repaired. The car may run slightly inefficiently and fail emissions, so schedule diagnosis soon to prevent catalytic converter damage from prolonged rich or lean operation.

Tools that help

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Guidance is general and written for Honda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.