P0139 fault code: O2 Sensor Circuit Slow OBDResponse

Can I drive with P0139? — Do not drive

We have no verified driving guidance for slow bank-1 post-catalyst oxygen response. We escalate to stop-until-checked rather than call it a mild emissions niggle. Lazy rear data is not a shopping-list for a new converter.

P0139 means “O2 Sensor Circuit Slow OBDResponse” — a fuel and air metering fault in the powertrain.

Can I DIY?

Professional-only boundary. Note P0139 and freeze-frame; slow rear-probe diagnosis is not a DIY ladder.

Do not DIYReviewed page boundary

ToolsSpecialist equipment

This is the conservative boundary from the reviewed code record. This page has no frozen site-wide safety grade, so it does not publish a repair route.

What to tell the garage about P0139

Do not drive. The downstream oxygen probe on bank 1 is reacting too slowly. A sluggish after-cat signal can make catalyst monitoring look wrong even when the brick itself has not been proven failed.

Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.

O2 Sensor Circuit Slow OBDResponse: Registration number
O2 Sensor Circuit Slow OBDResponse: Exact code P0139 and any companion codes
O2 Sensor Circuit Slow OBDResponse: Whether the engine management light is steady or flashing
O2 Sensor Circuit Slow OBDResponse: Recent MOT emissions result if you have it, plus any P0420-class companion

Copy this for an AI or your garage

Clipboard only — nothing is sent or stored by us. The text is this page’s title and drive guidance, ready to paste.

For an AI assistant

Fault code: P0139 — O2 Sensor Circuit Slow OBDResponse.
Can I drive: Do not drive. We have no verified driving guidance for slow bank-1 post-catalyst oxygen response. We escalate to stop-until-checked rather than call it a mild emissions niggle. Lazy rear data is not a shopping-list for a new converter.
Question: What does this code mean for a UK car, is it safe to drive, what are the most likely causes, and what should I ask a garage to check before replacing parts?

For your garage

REPAIR BRIEF — prepared by the owner with obdcode.co.uk
Fault code: P0139 — O2 Sensor Circuit Slow OBDResponse.
Drive guidance from obdcode.co.uk: Do not drive. We have no verified driving guidance for slow bank-1 post-catalyst oxygen response. We escalate to stop-until-checked rather than call it a mild emissions niggle. Lazy rear data is not a shopping-list for a new converter.
Owner’s request: please diagnose before replacing parts, itemise diagnosis time separately, and quote before any work beyond diagnosis.

P01xxFuel and air metering

MOT fail riskif the warning light stays on

What does P0139 mean?

P0139 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P01xx block, which covers fuel and air metering. The stored description is “O2 Sensor Circuit Slow OBDResponse”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0139 fail an MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off.

Before booking your test, check what usually fails on your car: see our MOT pass rates by make and model, built from 33.1 million DVSA tests.

P0100Mass or Volume Air Flow Circuit P0101Mass or Volume Air Flow Circuit Range/Performance P0102Mass or Volume Air Flow Circuit Low Input P0103Mass or Volume Air Flow Circuit High Input P0104Mass or Volume Air Flow Circuit Intermittent P0105Manifold Absolute Pressure/Barometric Pressure Circuit P0106Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance P0107Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

P0139 — quick answers

Is it safe to drive with P0139?

Do not drive. We have no verified driving guidance for slow bank-1 post-catalyst oxygen response. We escalate to stop-until-checked rather than call it a mild emissions niggle. Lazy rear data is not a shopping-list for a new converter.

Will P0139 fail my MOT?