P0137 fault code: O2 Sensor Circuit Low Voltage
Driveability guidance is not available for P0137 — treat as do not drive until checked. A low downstream oxygen-sensor voltage is not a cabin-safety all-clear; if you smell exhaust inside, or the light flashes, stop, get fresh air, and arrange recovery.
Can I DIY?
Professional-only boundary. You may confirm P0137 on a scanner; do not go under the car to reach the downstream sensor.
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 P0137
Stop driving now. P0137 is a low-voltage fault on the post-catalyst oxygen-sensor circuit (bank 1 sensor 2 on usual numbering). That monitor is not the same as the upstream probe. We have no verified drive rating — do not assume it is safe to keep driving.
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 Low Voltage: Registration number
- O2 Sensor Circuit Low Voltage: Exact code P0137 and any companion catalyst or upstream-sensor codes
- O2 Sensor Circuit Low Voltage: Whether the engine management light is steady or flashing
- O2 Sensor Circuit Low Voltage: Downstream (bank 1 sensor 2) voltage if the scanner showed it
- O2 Sensor Circuit Low Voltage: Whether anyone noticed exhaust smell, headache, or nausea in the cabin
Never open a hot coolant cap — pressure can scald you. Exhaust and catalytic converter get hot enough to burn and ignite debris. Stay clear of electric fans; they can run after shut-off.
Never idle in a closed garage to read codes — an open door is not enough. CO is odourless and can kill. Run diagnostics in open air. Headache or nausea with exhaust smell: get fresh air and stop.
Never go under a car held only by a jack. Use axle stands on the handbook support points, on firm level ground, with wheel chocks. No roadside or slopes. Rock-test before you go under.
What does P0137 mean?
P0137 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 Low Voltage”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.
Will P0137 fail an MOT?
If the engine management light is on with P0137 stored, that illuminated lamp is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. A downstream sensor fault can also leave catalyst monitoring incomplete.
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.
Related guides
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P0137 — quick answers
Is it safe to drive with P0137?
Stop driving now. Driveability guidance is not available for P0137 — treat as do not drive until checked. A low downstream oxygen-sensor voltage is not a cabin-safety all-clear; if you smell exhaust inside, or the light flashes, stop, get fresh air, and arrange recovery.
Will P0137 fail my MOT?
If the engine management light is on with P0137 stored, that illuminated lamp is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. A downstream sensor fault can also leave catalyst monitoring incomplete.
Fault-code identifiers are standard diagnostic facts. Their explanations and diagnostic guidance on this site are original editorial summaries, not reproduced SAE wording. MOT defect rules reflect the DVSA MOT inspection manual (2026). This page is general guidance for UK drivers, not a substitute for a professional diagnosis.