P0138 Subaru Code - HO2S12 Circuit High Voltage
Quick Answer
The Heated Oxygen Sensor 2 (HO2S) (Rear O2 Sensor), 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
- P0138 Subaru indicates HO2S12 Circuit High Voltage.
- 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 P0138 Subaru Description
What are the Possible Causes of the DTC P0138 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
- Intake air leaks
- Exhaust gas leaks
- Inappropriate fuel pressure
- Faulty fuel injectors
How to Fix the DTC P0138 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 P0138 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 P0138 Subaru Code
What does the OBDII code P0138 mean for a Subaru?
P0138 indicates high voltage in the downstream oxygen sensor (HO2S12), typically caused by issues with the sensor or related components.
What are common symptoms of P0138 on a Subaru?
Symptoms include reduced fuel efficiency, a check engine light, poor engine performance, and potentially an unusual smell from the exhaust.
What causes the P0138 code on a Subaru?
Common causes include a faulty downstream oxygen sensor, wiring issues, a short circuit, or an overly rich air-fuel mixture.
Can a dirty or clogged catalytic converter trigger the P0138 code?
Yes, a damaged or clogged catalytic converter can cause abnormal readings in the downstream oxygen sensor, leading to the P0138 code.
How do you diagnose the P0138 code in a Subaru?
Diagnosis involves inspecting the downstream oxygen sensor, checking for wiring damage, testing sensor voltage, and verifying proper air-fuel mixture levels.
Is it safe to drive a Subaru with the P0138 code?
While the vehicle may remain drivable, ignoring P0138 can lead to further damage, reduced fuel efficiency, and increased emissions.
How do you fix the P0138 code on a Subaru?
Repair may involve replacing the downstream oxygen sensor, fixing damaged wiring, or addressing issues with the catalytic converter or fuel system.
Can a vacuum leak cause the P0138 code?
No, vacuum leaks are unlikely to cause P0138, as this code relates specifically to high voltage in the downstream oxygen sensor circuit.
How much does it cost to fix the P0138 code on a Subaru?
The cost varies depending on the issue, with oxygen sensor replacement ranging from $100 to $300, including parts and labor.
Will clearing the P0138 code without repairs fix the issue permanently?
No, clearing the code without addressing the underlying problem will only temporarily reset the check engine light, and the issue will likely return.
Discuss the causes and fixes for P0138 Subaru OBDII Code
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