Heated Oxygen Sensor Heater Circuit Malfunction Bank 1 Sensor 2 (Ford)
What does P1139 mean?
The P1139 code means the vehicle's onboard diagnostic system has detected: Heated Oxygen Sensor Heater Circuit Malfunction Bank 1 Sensor 2 (Ford). This is a low severity code.
Common Symptoms
- Check Engine Light on
- Failed emissions test
- Slightly increased warm-up emissions
- No noticeable drivability symptoms
- Possible minor fuel economy decrease
Probable Causes (Ranked by Likelihood)
- Burned out O2 sensor heater element Very High
- Blown O2 sensor heater fuse High
- Open circuit in heater control wire Moderate
- Corroded O2 sensor connector Moderate
- PCM heater driver circuit failure Low
Step-by-Step Diagnostic Procedure
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Check the O2 sensor heater fuse in the underhood fuse box
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Measure O2 sensor heater resistance (should be 2-30 ohms depending on sensor type)
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Verify battery voltage is reaching the heater circuit at the sensor connector
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Inspect the sensor connector for corrosion or heat damage
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Replace the O2 sensor if the heater element has failed
Frequently Asked Questions
What does the O2 sensor heater do?
The heater element brings the O2 sensor up to operating temperature quickly after a cold start. Without the heater, the sensor takes longer to provide accurate readings, increasing cold-start emissions.
Can I drive with a bad O2 sensor heater?
Yes. A failed heater circuit will not significantly affect drivability. The engine runs in open loop longer during warm-up, but once the sensor reaches temperature from exhaust heat alone, it functions normally.
Why should I check the fuse first?
The O2 sensor heater fuse is shared among multiple sensors. If the fuse is blown, multiple heater codes may set. Replacing a $2 fuse is much cheaper than replacing a sensor unnecessarily.