P0138 on a Nissan: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to drive — this downstream sensor only monitors the catalytic converter, so a Nissan with P0138 can be driven while you arrange the repair.

What P0138 means on a Nissan

On a Nissan, P0138 means the engine computer sees high voltage from the bank 1 downstream oxygen sensor behind the catalytic converter. This sensor only monitors converter efficiency, so high voltage is almost always a faulty sensor or a wiring short rather than a rich fuel mixture.

Is P0138 common on Nissans?

P0138 appears most often on higher-mileage Nissans as the downstream sensor fails. Altima and Rogue models are common candidates, and an exhaust leak or failing converter can also push the downstream reading too high.

Commonly reported on: Altima, Rogue, Sentra, Pathfinder.

Symptoms

Check engine light on
Usually no change in how it drives
Possible reduced fuel economy
Sometimes no noticeable driving symptoms

Common causes

most common: Faulty bank 1 downstream oxygen sensor
common: Sensor wiring shorted to power
common: Exhaust leak before the sensor
less common: Failing catalytic converter

How to fix it

Fix	DIY?	Typical cost
Replace the bank 1 downstream oxygen sensor	Yes	$70–250
Repair shorted sensor wiring	Mechanic	$80–300
Replace the catalytic converter if it's failing	Mechanic	$800–2500