Engine-Codes - Generic - P1138

P1138 - Lack Of Heated Oxygen Sensor Switches Bank 1 Sensor 2 Switch Indicates Rich

Repair Importance Level: 3/3
Repair Difficulty Level: 2/3  What is this?
Table of contents

P1138 Possible Causes

  • Exhaust gas leaks
  • Faulty Heated Oxygen Sensor 2 (HO2S2) (Downstream) Bank 1
  • Heated Oxygen Sensor 2 Bank 1 harness is open or shorted
  • Heated Oxygen Sensor 2 Bank 1 circuit poor electrical connection
  • Inappropriate fuel pressure
  • Faulty fuel injectors

How is the P1138 code repair?

Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

What is the cost to diagnose the P1138 code

Labor: 1.0

The cost to diagnose the P1138 code is 1.0 hour of labor. The auto repair labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour.
How much do you know about cars?

Take the AutoCodes.com automotive tests and turbo-charge your car repair knowledge

Play Now

Possible Symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

P1138 Meaning

The Heated Oxygen Sensor 2 (HO2S2) (Downstream), after the 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 maintain near the ideal stoichiometric ratio. The HO2S2 output voltage changes suddenly in the vicinity of the stoichiometric ratio. The Powertrain Control Module (PCM) adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric. The HO2S2 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 PCM interprets Lean when the HO2S2 voltage is below 0.45 V. If the oxygen in the exhaust gas decreases, the air-fuel ratio becomes Rich. The PCM interprets Rich when the HO2S2 voltage is above 0.45 V. The P1138 code will set when the PCM detects that the HO2S2 signal is above the voltage of range for an extended period.

More Information

Need more information on how to fix the P1138 code?
Get Access to Factory Service Manuals

Information for specific makes

  • P1138 AUDI Long Term Fuel Trim Add. Fuel B2 System Too Lean  
  • P1138 BMW O2 Sensor Heater Circuit Low Voltage Bank 1 Sensor 2
  • P1138 BUICK HO2S Circuit High Voltage Sensor 2
  • P1138 CADILLAC HO2S Circuit High Voltage Sensor 2
  • P1138 CHEVROLET HO2S Circuit High Voltage Sensor 2
  • P1138 FORD Lack Of Heated Oxygen Sensor Switches Bank 1 Sensor 2 Switch Indicates Rich  
  • P1138 GMC HO2S Circuit High Voltage Sensor 2
  • P1138 INFINITI Swirl Control Valve Control System Performance
  • P1138 ISUZU HO2S 2 Voltage Stays High Rich Condition
  • P1138 LINCOLN Lack Of Heated Oxygen Sensor Switches Bank 1 Sensor 2 Switch Indicates Rich  
  • P1138 MAZDA Rear O2 Sensor Self Test Fault
  • P1138 MERCURY Lack Of Heated Oxygen Sensor Switches Bank 1 Sensor 2 Switch Indicates Rich  
  • P1138 MINI O2 Sensor Heater Circuit Low Voltage Bank 1 Sensor 2
  • P1138 NISSAN Swirl Control Valve Control System Performance
  • P1138 PONTIAC HO2S Bank 1 Sensor 2 Rich or High Voltage
  • P1138 SATURN HO2S Bank 1 Sensor 2 Rich or High Voltage
  • P1138 SUZUKI HO2S Circuit High Voltage During Decel Fuel Cut-Off Sensor 2
  • P1138 VOLKSWAGEN Long Term Fuel Trim Add. Fuel B2 System Too Lean  

Need more help?

Get the P1138 code diagnosed by a professional: Find a repair shop in your area