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P1166/P1167 Fault Code on 2000 Honda Accord 4Cyl F23A4 Engine - Open Loop O2 Sensor Issue

Model: 2000 Honda Accord Fault Code: P1166 Posted: 2007-10-05 08:21

I'm experiencing a P1166 and P1167 diagnostic trouble code on my 2000 Honda Accord with the 4-cylinder F23A4 engine. My ProScan laptop shows an open-loop reading from the oxygen (O2) sensors, specifically at the sensor located before the catalytic converter. When I test the wiring harness using a test light, only one circuit lights up—indicating power presence—even when the key is on and the engine is running. This suggests a potential power issue to the O2 sensor. I've heard that O2 sensors may have internal fuses, but I cannot locate any fuse related to this system. Is there a way to verify if the sensor itself is receiving proper voltage or signal integrity? Additionally, I'd appreciate insights into whether these codes are commonly caused by faulty oxygen sensors, especially given that aftermarket products seem to perform poorly with Honda vehicles. Thank you for your guidance, Jim.

Related fault codes
P1166P1167
Comments (5)
Anonymous 2007-10-05 09:04

A digital voltmeter (DVM) is required to properly test an O2 sensor—just checking for power doesn't confirm sufficient current or signal integrity. The presence of voltage on the heater circuit does not guarantee a functional sensor; you need to verify both heater operation and actual signal output.

Anonymous 2007-10-06 04:08

My ProScan also shows 'Short Turn Trim Bank 1' and 'Long Turn Trim Bank 1' as zero, while Bank 3 reads 100.78 / 100.78 for both short and long terms. These values differ from what I observed in my other vehicle—does this indicate a system anomaly or just normal variation? The online resources often point to O2 sensor failure as the root cause, but I'd like to confirm this before replacing any components, especially since aftermarket sensors don't perform well with Honda engines.

Anonymous 2007-10-06 10:49

A failed oxygen sensor can significantly impact fuel trim calculations. Can you create a condition—such as an over-lean or over-rich mixture—and monitor the O2 sensor reading on your scan tool to see if it responds? This test helps determine whether the sensor is functioning correctly.

Anonymous 2007-10-06 12:09

How can I induce such conditions with my ProScan dongle connected to a laptop? I believe my device only reads data and lacks bi-directional communication with the ECM. Is there an alternative method to simulate rich or lean mixtures without direct control from the scanner?

Anonymous 2007-10-06 16:12

Jim, your laptop-based ProScan cannot send commands to the ECU because it lacks bi-lateral control. To test sensor responsiveness, disconnect a vacuum line or spray carburetor cleaner into the intake manifold—this will create a lean condition (vacuum leak) or rich condition (cleaner). Observe if the O2 sensor reading shifts accordingly. If no response occurs, the sensor is likely stuck and should be replaced. This is a common diagnostic step when suspecting a faulty O2 sensor.