P1167
Air/Fuel Ratio Sensor 1 Heater System Malfunction
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The P1167 code on Subaru vehicles means the Air/Fuel Ratio Sensor 1 heater system is malfunctioning — specifically, the sensor has not achieved the minimum specified voltage within the ECM's expected time window. This code is closely related to P1166 but focuses on the overall heater system performance rather than just the circuit. The heater is critical because the A/F sensor must reach approximately 1,200°F to produce accurate readings. Until it reaches that temperature, the engine runs on a pre-programmed rich fuel map.
P1166 and P1167 frequently appear together, and in most cases they point to the same failed A/F sensor. The internal heater element wears out over time, and once its resistance changes enough, it can no longer heat the sensor adequately. Before replacing the sensor, it's worth checking the basics: verify the heater fuse is intact, inspect the wiring for heat damage, and ensure your battery and alternator are providing proper voltage.
The vehicle is safe to drive with this code, but your fuel economy will suffer, especially on short trips where the engine doesn't have time to fully warm up. Plan to address it within the next few weeks. If you're comfortable working near the exhaust manifold, replacing the A/F sensor is a moderate DIY repair. Use an OEM or quality aftermarket sensor — cheap sensors are prone to premature heater failure.
Severity
Symptoms
- •Check engine light illuminated
- •Decreased fuel economy during short trips and cold starts
- •Engine takes longer to warm up and run smoothly
- •Slightly rough idle when engine is cold
- •Mild exhaust smell during initial startup
Likely Causes
The A/F sensor's heater element does not achieve the required voltage threshold, indicating the heater has degraded or failed. The sensor itself is the most commonly replaced part for this code.
Heat-damaged or corroded wiring between the sensor and the ECM prevents the heater from receiving adequate voltage. This is common in higher-mileage vehicles where exhaust heat degrades wire insulation.
If the vehicle's charging system is weak, the heater circuit may not receive enough voltage to bring the sensor to operating temperature within the ECM's expected timeframe.
High resistance at the sensor connector or a poor engine ground prevents sufficient current flow to the heater, causing it to underperform even if the sensor itself is functional.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the upstream air/fuel ratio sensor (Bank 1 Sensor 1)
- Test and repair wiring harness for the heater circuit
- Check battery and alternator output to ensure adequate system voltage
- Clean or replace sensor connector and check engine grounds