CodeXOBD

P0136 — O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

P0136 means the module detected a fault in the downstream oxygen sensor circuit after the catalytic converter. A failed sensor or wiring problem is the most common cause.

Low

The engine runs normally. The only effect is that the module cannot monitor catalytic converter efficiency, which may hide a converter problem.

$20–$200Parts, typical range
0.3–1 hLabour
estimateNot a quote · 2026 basis

What P0136 means

The downstream oxygen sensor monitors catalytic converter efficiency by comparing its reading to the upstream sensor. P0136 sets when this sensor's signal is out of range or not responding. Unlike the upstream sensor, the downstream sensor should be relatively stable — it does not oscillate rapidly. A failed downstream sensor prevents the module from monitoring converter efficiency and can mask a genuinely failing converter.

Technical summary
SystemEmission control
How the catalytic converter is gradedExhaust leaves the engine, passes the upstream oxygen sensor, then the catalytic converter, then the downstream oxygen sensor. The module compares the two sensor signals: on a healthy converter the downstream signal is steady while the upstream one oscillates. When the downstream signal starts to mirror the upstream one, the converter is judged to have stopped storing oxygen.Engineexhaust outUpstream O₂sets fuel trimCatalytic converterstores oxygenDownstream O₂grades the converterThe module compares the two sensors — that comparison is the test

Symptoms you may notice

What causes P0136

Downstream oxygen sensor has failed

Very likelylow costeasy

The sensor's internal element has degraded, producing a stuck or out-of-range signal.

Wiring or connector damaged

Likelylow costeasy

Heat from the exhaust pipe damages the sensor harness over time. Check for chafing and melted insulation.

Exhaust leak near the downstream sensor

Possiblelow costmoderate

A leak between the converter and the sensor lets ambient air in, producing erratic or out-of-range readings that the module flags as a circuit fault.

How to diagnose it

1

Monitor downstream sensor voltage

With the engine warm at steady cruise, the downstream sensor should read a relatively stable 0.5-0.7V. Rapid oscillation or a stuck reading indicates a fault.

Tools: OBD-II scanner with live dataExpected: Steady 0.5-0.7V at cruiseIf it passes: Sensor is reading correctly. The fault may be intermittent.If it fails: Stuck at one voltage or oscillating like the upstream — replace the sensor.
2

Inspect wiring and connector

Check the downstream sensor harness for chafing, melted insulation, and corroded connector pins.

Tools: Inspection lightIf it passes: Wiring is intact. The sensor is confirmed faulty.If it fails: Repair the wiring or clean the connector.
3

Check for exhaust leaks between the converter and sensor

Inspect the exhaust pipe between the catalytic converter and the sensor for leaks. Look for soot marks or listen for ticking at idle.

Tools: Inspection lightIf it passes: No leaks found. Replace the sensor.If it fails: Repair the exhaust leak, clear the code, and re-test.

Related codes

P0130P0137P0138P0140P0420

Common questions

Is P0136 serious?

Not for the engine — it runs fine. But it prevents the module from detecting a failing catalytic converter, so you could be driving with a bad converter and not know it.

Last verified 2026-07-27 · Sources: SAE J2012 — Diagnostic Trouble Code Definitions and Failure Type Byte (SAE International)

This information is for general guidance and is not a substitute for professional diagnosis. Cost figures are estimates, not quotes.