P0138 on a Honda: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

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

What P0138 means on a Honda

On a Honda, P0138 means the engine computer sees high voltage from the bank 1 downstream oxygen sensor, located after the catalytic converter. This sensor only checks converter efficiency, so high voltage is almost always a faulty sensor, a wiring short, or a converter issue — not a rich-running engine.

Is P0138 common on Hondas?

P0138 is most common on higher-mileage Hondas as the downstream sensor fails. Civic, Accord, and CR-V models see it regularly, and wiring damaged by rodents is a known cause on Hondas.

Commonly reported on: Civic, Accord, CR-V, Pilot.

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: Wiring damaged by rodents
less common: Failing catalytic converter

How to fix it

Fix	DIY?	Typical cost
Replace the bank 1 downstream oxygen sensor	Yes	$70–240
Repair shorted or rodent-damaged sensor wiring	Mechanic	$80–300
Replace the catalytic converter if it's failing	Mechanic	$800–2500