P0139 Subaru Code - HO2S12 Circuit Slow Response
Quick Answer
The Heated Oxygen Sensor 2 (HO2S), after three way catalyst (manifold), monitors the oxygen level in the exhaust gas on each bank. Common causes include Faulty Rear Heated Oxygen Sensor Bank 1, Rear Heated Oxygen Sensor Bank 1 harness is open or shorted, Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
- What it means
- P0139 Subaru indicates HO2S12 Circuit Slow Response.
- Common causes
- Common causes include Faulty Rear Heated Oxygen Sensor Bank 1, Rear Heated Oxygen Sensor Bank 1 harness is open or shorted, Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection.
- Severity
- Moderate - service should be scheduled soon.
- Can I drive?
- The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
Code P0139 Subaru Description
What are the Possible Causes of the DTC P0139 Subaru?
- Faulty Rear Heated Oxygen Sensor Bank 1
- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks
How to Fix the DTC P0139 Subaru?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
Code Tech Notes
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0139 Subaru code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Frequently Asked Questions about P0139 Subaru Code
1. What does the OBDII code P0139 mean for a Subaru?
P0139 indicates that the downstream oxygen sensor (HO2S12) in Bank 1 is responding too slowly to changes in the air-fuel mixture, which could affect emissions.
2. What are the common symptoms of Subaru code P0139?
Symptoms may include the check engine light turning on, decreased fuel efficiency, failed emissions tests, and occasional rough idling.
3. What causes the P0139 code to appear on a Subaru?
Common causes include a failing downstream oxygen sensor, exhaust leaks, wiring or connector issues, or a rich/lean air-fuel mixture.
4. Can I drive my Subaru with a P0139 code?
While you can drive with this code, it’s not recommended as it can lead to increased emissions and potentially damage the catalytic converter over time.
5. How do I fix the P0139 code on my Subaru?
Fixes include inspecting and replacing the downstream oxygen sensor, repairing damaged wiring or connectors, and checking for exhaust leaks or air-fuel ratio issues.
6. How much does it cost to repair code P0139 on a Subaru?
Repair costs vary but typically range from $150 to $300 for parts and labor if replacing the oxygen sensor.
7. Can a dirty air filter cause a P0139 code on a Subaru?
A dirty air filter is unlikely to directly cause P0139, but it can affect engine performance and air-fuel mixture, which may contribute to related issues.
8. How can I diagnose the P0139 code on my Subaru?
Use an OBDII scanner to confirm the code, then inspect the downstream oxygen sensor, wiring, and exhaust system for damage or leaks.
9. Does a P0139 code always mean the oxygen sensor is bad?
No, the issue could be due to wiring problems, exhaust leaks, or other factors affecting sensor performance, not just a faulty sensor.
10. Will clearing the P0139 code fix the problem on my Subaru?
Clearing the code may temporarily turn off the check engine light, but it won’t fix the underlying issue causing the slow sensor response.
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