← Back to list

Error Codes P0146 and P0043 on 2008 Nissan Altima: O2 Sensor Replacement Not Resolving Check Engine Light

Model: Nissan Altima Fault Code: P0043 Posted: 2017-01-05 09:27

Hello, I'm looking for help diagnosing a persistent check engine light on my 2008 Nissan Altima. The dealership replaced the oxygen (O2) sensor, but the warning light remained on. I then installed a different brand O2 sensor, yet the issue persists. The vehicle is now due for an inspection this month, and I'm concerned about what else might be causing the engine light to stay active. I've been researching the error codes: P0146 indicates an out-of-range voltage signal from the oxygen sensor, while P0043 points to a voltage issue on the O2 heater circuit. Could there be another underlying problem preventing the system from resetting? I'm considering replacing the sensor with a genuine Nissan OEM unit, as aftermarket sensors may not meet emission standards. Any insights or troubleshooting steps would be greatly appreciated.

Related fault codes
P0043P0146
Comments (4)
Anonymous 2017-01-05 11:13

The P0043 code suggests a voltage issue on the O2 heater circuit, while P0146 indicates an out-of-range signal voltage. To diagnose this accurately, use a scan tool or digital multimeter (DVOM) to check the heater circuit voltage and signal return. The red/yellow wire at the sensor should show 12V when the engine is off (KOEO). Also verify that the underhood fuse #37 is intact—this fuse powers the O2 heater circuit, especially in California-emission vehicles.

Anonymous 2017-01-05 12:03

That makes sense—the voltage issues could be related to wiring or a faulty relay. I didn- t go with a Nissan OEM sensor due to cost concerns. Should I check the O2 heater circuit relay? It's possible that a defective relay is causing intermittent signal problems even after replacing the sensor.

Anonymous 2017-01-05 14:41

Before replacing any components, double-check the wiring diagram for the O2 sensor harness. Specifically test the red/yellow wire at the sensor with the engine off (KOEO) to confirm it has a solid 12V supply. Also ensure that fuse #37 under the hood is properly rated and not blown—this fuse is critical for heater circuit operation in California-compliant vehicles.

Anonymous 2017-01-05 16:17

I haven't checked the wiring diagram yet, but I'll do so as soon as possible. Once I've tested the voltage and confirmed the fuse status, I’ll update this thread with my findings. Thanks for all the helpful input—this is really clarifying what might be going on.