Code: P0158

O2 Sensor Circuit High Voltage – Bank 2 Sensor 2

What it means

Bank 2 = the side of the engine without cylinder #1

Sensor 2 = downstream (after the catalytic converter)

The ECU is seeing too high voltage from the rear O2 sensor (usually >0.9V for too long)

Downstream sensors should be fairly stable, not stuck high.

Common Causes (Most to Least Likely)

✅ 1. Faulty O2 sensor (most common)

Internal short

Contaminated sensor (oil, coolant, silicone, fuel additives)

Sensor stuck rich

👉 Very common fix

✅ 2. Wiring issue

Signal wire shorted to:

Battery voltage

Heater power wire

Melted wiring near exhaust

Poor ground

👉 Check harness routing near the cat & exhaust

✅ 3. Exhaust problem

Exhaust leak before sensor

Restricted or damaged catalytic converter

Backpressure causing rich readings

✅ 4. Engine running rich

(less common for a rear sensor code, but possible)

Leaking injector (Bank 2)

High fuel pressure

EVAP purge stuck open

❌ Rare causes

PCM failure (very rare — rule everything else out first)

Quick Diagnostic Steps (Shop Process)

Step 1: Scan Tool Check

Monitor Bank 2 Sensor 2 voltage

Normal: 0.6–0.8V (mostly steady)

Faulty: Stuck above 0.9–1.0V

👉 If it’s stuck high → continue

Step 2: Unplug the Sensor

Voltage should drop to 0V

If it stays high → wiring short to power

If it drops → sensor is bad

✅ This test alone often confirms the fault

Step 3: Inspect Wiring

Look for:

Melted insulation

Harness touching exhaust

Corrosion in connector

Pay attention to heater circuit wires

Step 4: Check Exhaust

Inspect for leaks before sensor

If cat is rattling or overheating → possible restriction

Typical Repair

✅ Replace Bank 2 Sensor 2

Clear codes

Test drive

Confirm downstream voltage stabilizes

⚠️ Do NOT replace the catalytic converter unless you confirm it’s bad — many shops misdiagnose this code.

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