On a 2003 Honda CR-V, a P1166 code typically points to a problem with the air-fuel ratio (A/F) sensor heater circuit — specifically for the primary (upstream) A/F sensor located before the catalytic converter.
Here's where to find them:
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Air-Fuel Ratio Sensor (Primary/Upstream O2 Sensor):
Located on the exhaust manifold, just as the exhaust exits the engine. You’ll usually see it sticking out with a wire leading back to the engine harness. This is the sensor the P1166 code is referring to. -
Secondary (Downstream) O2 Sensor (Heated O2 Sensor - HO2S):
Found after the catalytic converter, underneath the vehicle, in the exhaust pipe. It’s not the one related to this code, but good to know its location.
If you're troubleshooting this yourself, start by checking the wiring and connector for damage or corrosion. If everything looks good, the A/F sensor itself is likely bad and will need replacing.
Fortunately, the service manual will walk you through testing and replacement procedures with connector pinouts, resistance specs, and exact routing — a no-brainer to get if you ask me, especially if you're solving this DIY style ✌🏻
