AutoCodes – Ford – P0138 Ford

P0138 Ford Code - O2 Sensor Circuit High Voltage Bank 1 Sensor 2

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 Ford indicates O2 Sensor Circuit High Voltage Bank 1 Sensor 2.
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.

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Code Popularity 49,312

How popular is this code, among other codes? Medium

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 14, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
Comments
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Code P0138 Ford Description

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. For optimum catalyst operation, the air fuel mixture (air-fuel ratio) must be maintained near the ideal stoichiometric ratio. The HO2S output voltage changes suddenly in the vicinity of the stoichiometric ratio. The Engine Control Module (ECM) adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric. The HO2S generates a voltage between 0.1 and 0.9 V in response to oxygen in the exhaust gas. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes Lean. The ECM interprets Lean when the HO2S voltage is below 0.45 V. If the oxygen in the exhaust gas decreases, the air-fuel ratio becomes Rich. The ECM interprets Rich when the HO2S voltage is above 0.45 V.

OBDII Code P0138 Ford - O2 Sensor Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com — P0138 Ford Code - O2 Sensor Circuit High Voltage Bank 1 Sensor 2

What does this mean?

What are the Possible Causes of the DTC P0138 Ford?

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 Ford?

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.

What does this mean?

Code Tech Notes

Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0138 Ford 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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Information for Specific Ford Models

P0138 1997 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 1998 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 1999 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2000 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2001 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2002 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2003 Ford F150 — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2006 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2007 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2008 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2009 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2010 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2011 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 2012 Ford Fusion — O2 Sensor Circuit High Voltage Bank 1 Sensor 2

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.