P0158 OBD2 Code on 2006 Dodge Stratus 2.7L: Diagnosis and Fix Guide

I recently encountered P0158 on my 2007 Dodge Stratus 2.7L — any success so far? Are there no other related codes? Did you replace the oxygen sensor, and if yes, was it a genuine Dodge part or aftermarket? Was the negative battery cable disconnected before testing? Which wire showed 0.63 volts — was this voltage stable after reconnection? My suspicion is that an aftermarket sensor may be at fault, and the negative cable wasn’t removed — could this be the issue?

The power supply to the heater circuit showed the correct voltage. I used NGK spark plugs. The issue was resolved using an Innovaa 3160B scanner, and the voltage stabilized after a proper engine condition (lean/rich) adjustment. Voltage readings do vary based on whether the engine is leaning or running rich.

To clear stored fault data, you must disconnect the negative battery cable — this should be done before any further diagnostics. O2 sensors are only read when the engine is running; we need to observe the sensor's signal swing between rich and lean conditions for accurate diagnosis.

The post-cat oxygen sensor on the left bank shows high voltage. Start the car and monitor the post-cat O2 sensor reading via your scan tool — is it above 1.2 volts? If yes, disconnect the O2 sensor connector — does the voltage remain above 1.2 volts in the scan tool? Use a digital voltmeter (DVOM): connect negative to a solid ground and positive to the pink/white signal wire at the harness side with the connector disconnected while the engine is running. What do you read? The signal wire should be the pink/white. I recently fixed a GM vehicle where a rich condition caused high voltage on the post-cat O2 sensor — this would appear in your STFT and LTFT values. Check your STFT and LTFT at idle and under load. Report back — are there any exhaust leaks?

With the sensor unplugged, I read 1.27 volts on the scan tool. When the wire was disconnected (pink/white), the voltage dropped to 0.5 volts. No exhaust leaks were detected.

Is it correct that the scan tool reads 1.27 volts with the sensor plugged in and 0.5 volts when unplugged, both while the engine is running?

STFT for Bank 1 is bouncing — Bank 2 STFT ranges from -4.7 to +6.3. LTFT values for cylinders 1 and 2 are consistently at zero.

A variation of ±10% is acceptable, but ideally the value should be close to zero. You need to check fuel trims across different RPMs — idle, 1500 RPM, and 3000 RPM. If disconnecting the O2 sensor causes a drop in scan tool voltage, this may indicate either a rich condition or a faulty oxygen sensor. Is it correct that with the sensor plugged in you read 1.27 volts and 0.5 volts when unplugged while running?

The 0.5-volt reading was measured at the pink/white wire when the O2 sensor connector was disconnected.

What does your scan tool show with the engine running and the O2 sensor connector disconnected?