Professional Automotive Advice

Definition of Trouble Code P0138

Trouble code P0138 refers to an issue with the Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2). This code indicates that the Engine Control Module (ECM) has detected a high voltage signal from the oxygen sensor located in the downstream of the catalytic converter. The oxygen sensor monitors the levels of oxygen in the exhaust gases, and a high voltage signal may suggest an inefficient catalytic converter or an issue with the sensor itself.

Diagnosing Trouble Code P0138

To diagnose the problem causing trouble code P0138, follow these steps:

Step 1: Visual inspection

Begin by examining the oxygen sensor and its wiring. Look for any signs of damage, corrosion, or loose connections. If you find any issues, repair or replace the necessary components.

Step 2: Check for related trouble codes

Using an OBD-II scanner, check for any other related trouble codes. These codes can provide additional information on the root cause of the P0138 code.

Step 3: Test the oxygen sensor

Using a digital multimeter, measure the voltage output of the oxygen sensor while the engine is running. If the voltage is consistently above 0.9 volts, it indicates a high voltage issue. In such cases, the oxygen sensor should be replaced.

Step 4: Inspect the catalytic converter

Examine the catalytic converter for any signs of damage, clogging, or overheating. A faulty catalytic converter can cause the oxygen sensor to send a high voltage signal to the ECM.

Repairing Trouble Code P0138

Based on the diagnosis, follow these steps to repair the issue causing the P0138 code:

Step 1: Repair or replace damaged wiring or connectors

If you found damaged wiring or connectors during the visual inspection, repair or replace them as necessary.

Step 2: Replace the oxygen sensor

If the voltage output of the oxygen sensor was found to be consistently high, replace the oxygen sensor (Bank 1 Sensor 2) with a new one.

Step 3: Address any related trouble codes

If other trouble codes were found during the diagnosis, address them accordingly. This may involve repairing or replacing additional components.

Step 4: Replace the catalytic converter (if necessary)

If the catalytic converter was found to be damaged, clogged, or overheating, replace it with a new one.

Conclusion

Trouble code P0138 - Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2) - can be caused by various issues, including damaged wiring, a faulty oxygen sensor, or an inefficient catalytic converter. By following the step-by-step guide provided, you can diagnose and repair the issue causing the P0138 code. After repairing the problem, use an OBD-II scanner to clear the trouble code and verify that the issue has been resolved.