P0152-00: O2 Sensor Circuit High Voltage (Bank 2, Sensor 1)

🔧 What P0152 Means

Bank 2 Sensor 1 (upstream O2) is reporting a high voltage signal (usually >0.9–1.0V) for too long.

👉 This sensor is before the catalytic converter on Bank 2 (the bank without cylinder #1).

🚨 Common Causes (Most to Least Likely)

1. Rich Running Condition (MOST COMMON)

The sensor is doing its job and reporting rich exhaust.

Possible reasons:

Leaking fuel injector (Bank 2)

High fuel pressure

Faulty fuel pressure regulator

EVAP purge valve stuck open

MAF sensor dirty or skewed

Engine coolant temp sensor reading cold

✅ Check fuel trims:

Short-term trim negative (-10% to -25%) = rich condition confirmed

2. O2 Sensor Signal Shorted to Voltage

Signal wire shorted to 12V or heater circuit

Melted wiring near exhaust

Improper aftermarket sensor wiring

🔍 Key check:

Unplug sensor → voltage should drop to ~0V

If voltage stays high → wiring/PCM issue

3. Faulty O2 Sensor (Less Common Than People Think)

Sensor internally stuck high

Contaminated (oil, coolant, silicone)

⚠️ Don’t replace until wiring & fuel trims are checked.

4. Exhaust Leak (Rare for High Voltage)

Upstream leaks usually cause lean codes, but extreme conditions can confuse readings.

🧪 Quick Diagnostic procedure

Step 1: Identify Bank 2

Bank 2 = side without cylinder #1

Inline engines → no Bank 2

Step 2: Scan Tool Data (Key Step)

Monitor:

B2S1 O2 voltage

Short-Term Fuel Trim (STFT)

Long-Term Fuel Trim (LTFT)

Normal behavior:

O2 voltage should switch 0.1–0.9V

Stuck at 0.9–1.2V = problem

Step 3: Induce Lean Condition Test

Create a small vacuum leak

Snap throttle

If voltage does NOT drop → sensor or wiring issue
If voltage drops normally → engine running rich

Step 4: Unplug O2 Sensor

Voltage should drop to near 0V

If still high → wiring short or PCM fault

Step 5: Fuel System Checks (If Rich)

Injector balance test (Bank 2)

Fuel pressure test

Check purge valve operation

Compare MAF grams/sec to known good values

🛠️ Common Missdiagnosis‏

❌ Replacing O2 sensor without checking fuel trims
❌ Ignoring leaking injectors
❌ Not identifying correct bank

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