OBD-II Code P0136 — What It Means & How to Fix It

What Does This Error Mean?

P0136 means there is a problem with the oxygen sensor circuit on Bank 1, Sensor 2. This is the downstream oxygen sensor — located after the catalytic converter. The ECM detected that the sensor's output is not within the expected range. Common causes are a failed oxygen sensor, wiring damage from heat, or a bad electrical connection. In most cases, you won't notice drivability problems — but your check engine light will stay on.

Affected Models

All vehicles 1996+
Common in Toyota Camry
Common in Ford Explorer
Common in Dodge Charger
Common in Subaru Forester

Common Causes

Failed Bank 1 Sensor 2 oxygen sensor with an open or shorted internal circuit
Heat-damaged wiring harness melted from proximity to the catalytic converter
Corroded or broken connector at the downstream oxygen sensor
Open ground circuit for the sensor preventing accurate voltage readings
ECM driver circuit fault affecting the sensor reference signal (rare)

How to Fix It

Locate the Bank 1 Sensor 2 oxygen sensor. It is threaded into the exhaust pipe behind the catalytic converter on the Bank 1 side of the engine. Look for a sensor with a 1-2 foot wiring pigtail plugged into a connector.

Bank 1 is the side of the engine with cylinder number 1. On four-cylinder engines, there is only one bank, so this is the only downstream sensor.
Inspect the wiring carefully. The downstream sensor sits near the very hot catalytic converter. Look for melted, cracked, or brittle insulation along the wire from the sensor to the connector. This heat damage is a very common cause of P0136.

Even minor cracking can cause intermittent shorts or open circuits that set this code. Damaged wiring should be repaired or replaced with high-temperature wire rated for exhaust proximity.
Unplug the connector and look inside for corrosion, green oxidation, or bent terminals. Clean with electrical contact cleaner. Push the connector back together firmly — it should click into place.

A poor connection at the sensor connector can create the same symptoms as a completely failed sensor. Always check the connector before ordering a replacement part.
Use a multimeter to test the sensor. Probe between the signal wire and ground. On a warm engine, the signal should fluctuate slightly — a completely dead reading (0 volts or 5 volts stuck) means the sensor has failed.

Unlike the upstream sensor, the downstream sensor's output is much more stable (less switching). It should read around 0.6-0.9 volts on a well-functioning catalytic converter.
Replace the sensor if it fails testing or if the wiring looks burned. Use an OEM or quality aftermarket sensor. Apply anti-seize if the threads are not pre-coated. Clear the code and verify the repair with a short drive.

An oxygen sensor socket (with a side slot for the wire) makes removal and installation much easier. Most auto parts stores will lend one for free with a deposit.

When to Call a Professional

P0136 is typically an affordable repair — usually just the sensor or wiring. A downstream O2 sensor replacement costs $80-$200 at most independent shops. If the wiring harness is severely heat-damaged, a mechanic should inspect and repair it properly. Leaving P0136 unresolved prevents accurate catalytic converter monitoring. This can mask a failing converter, which costs $500-$2,500 to replace if caught too late.

Frequently Asked Questions

Does the downstream sensor affect how the engine runs?

Not directly — the upstream sensor (Sensor 1) controls fuel mixture. The downstream sensor mainly monitors catalytic converter performance. A bad Sensor 2 should not change how your engine idles or accelerates. However, if the ECM cannot trust Sensor 2, it may adjust fuel trims incorrectly over time. Fix it to keep your exhaust monitoring system working properly.

Can a bad catalytic converter cause P0136?

Occasionally, yes. A severely degraded catalytic converter produces unusual exhaust chemistry. This can cause the downstream sensor to output abnormal readings. But P0136 is more commonly the sensor or wiring itself — not the converter. If you also have P0420 (catalyst efficiency below threshold), focus on the converter.

How long can I drive with P0136?

You can drive with P0136 for a while — drivability is usually unaffected. However, with this code active, the ECM cannot properly monitor your catalytic converter. A failing converter could go undetected for longer than normal. Fix the sensor within a few weeks to keep your emissions monitoring system accurate.