P0138 Honda

P0138 Honda - HO2S Bank 1 Sensor 2 Circuit Low Voltage

Repair Importance Level: 3/3
Repair Difficulty Level: 2/3  What does this mean?
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P0138 Honda Comments |  Add Comment
Possible causes
- 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
What does this mean? What does this mean?
Tech notes
Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem.
What does this mean? What does this mean?
When is the code detected?
The P0138 code is set when the Engine Control Module (ECM) detects that the rear O2 sensor signal voltage remains excessively high for an extended period of time.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- High Fuel Consumption
- Excessive Smoke from Exhaust
P0138 Honda 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 Honda - HO2S Bank 1 Sensor 2 Circuit Low Voltage - Engine-Codes.com
P0138 Honda Information for specific Honda models
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HONDA Technical Service Bulletins for P0138 code
2001 HONDA CIVIC Engine And Engine Cooling:exhaust System:emission Control Details
2001 HONDA CIVIC Unknown Or Other Details
What does this mean? What does this mean?
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Repair Importance Level
3
1=Low 2=Medium 3=High What does this mean?
Repair Difficulty Level
2
1=Easy 2=Moderate 3=Hard What does this mean?
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