O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
Code P0138 indicates that downstream Oxygen Sensor 2 on Bank 1 is outputting sustained high voltage (above 0.99V to 1.2V) for more than 2 minutes. The most common cause is internal shorting inside the sensor or water intrusion into the underbody wiring harness connector.
Unplug the downstream O2 sensor harness under the vehicle. Inspect for water or oil contamination inside the connector pins. If clean and voltage remains >1.0V with engine idling, replace the downstream oxygen sensor.
Interactive Symptom Pinpoint Troubleshooter
Answer 2 diagnostic tests to isolate the exact component failure for P0138.
Does the downstream O2 sensor voltage drop to 0V when you unplug the sensor completely?
Live Scanner & Multimeter Benchmark Values
Compare your live OBD-II PID sensor data against OEM factory operating specs for P0138.
| Monitored Parameter / Sensor PID | Healthy OEM Operating Range | Fault Threshold (Triggers P0138) |
|---|---|---|
| Downstream O2 (B1S2) Voltage at Warm Idle | 0.5V – 0.8V steady DC | >1.0V (indicates 12V heater wire shorting to 1V signal wire) |
| Sensor Heater Resistance | 6.0 – 16.0 Ohms | <2.0 Ohms (internal short circuit) |
Symptoms Associated with P0138
Drivers typically observe the following symptoms when the ECM flags P0138:
Common Root Causes & Statistical Probability Matrix
Statistical breakdown of what triggers this code based on automotive repair shop data.
Step-by-Step Diagnostic & Repair Procedure
Follow this logical order to isolate and repair P0138 before spending money on costly parts.
Step 1: Unplug Sensor Test
Unplug sensor while viewing live data. If voltage drops from 1.2V to 0.45V, sensor is bad.
Step 2: Inspect Harness Loom
Inspect wire routing along exhaust pipe for melted insulation.
Step 3: Replace Sensor
Unscrew with slotted socket and anti-seize threads.
Vehicle-Specific Failure Trends & Technical Bulletins
Real workshop failure patterns reported by mechanics across popular makes and models for P0138.
Dodge Charger / Ram 1500 (5.7L Hemi)
Toyota Corolla / Camry
Dave Miller, ASE Master Tech
ASE L1 Certified Master ReviewerASE Certified Master Automobile Technician (A1-A8) & L1 Advanced Engine Performance • 24 years automotive diagnostic experience
“Always verify sensor voltages and harness grounds before purchasing replacement electronic components.”