P0138 on a Lexus: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

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

What P0138 means on a Lexus

On a Lexus, 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, a wiring short, or a converter problem — not a rich-running engine.

Is P0138 common on Lexuss?

P0138 is most common on higher-mileage Lexus models as Denso downstream sensors fail with age. RX and ES models see it regularly, and wiring damaged by rodents is a known cause on Lexus vehicles.

Commonly reported on: ES, RX, GX, NX.

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 with an OE-quality Denso unit	Yes	$80–300
Repair shorted or rodent-damaged sensor wiring	Mechanic	$100–350
Replace the catalytic converter if it's failing	Mechanic	$800–2500