P0158
O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
Powertrain Emission Controls Post-Catalyst O2 Sensor 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your downstream oxygen sensor on bank 2 is sending a weak electrical signal to the engine computer, like a battery with low voltage trying to power a device. The ECU expects a certain voltage range to monitor exhaust oxygen levels, but this sensor is reading too low.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Rough idle or hesitation during acceleration
Decreased fuel economy
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the O2 sensor output voltage to adjust the air-fuel mixture. Bank 2 Sensor 2 is the downstream sensor after the catalyst converter. When voltage stays below the normal threshold for a set duration, the fault is logged.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
O2 Sensor Voltage 0.4 - 0.9 volts (fluctuating) Below 0.3 volts for extended period
Sensor Response Time Less than 100 ms Slow or no response to load changes
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Oxygen sensor connector and wiring
Inspect for corrosion, loose pins, or damaged insulation in the sensor harness and clean contacts.
2
O2 Sensor (Bank 2, Sensor 2)
Remove and replace the downstream oxygen sensor with an OEM or quality replacement if wiring is intact.
3
ECU software update or PCM reset
If sensor and wiring are good, perform a full system scan and consider a dealer reprogram.