Failed rear oxygen sensor, including a shorted heater circuit inside the sensor, which often also blows the heater fuse (OBD-Codes.com). Shorted signal circuit in the sensor (OBD-Codes.com). Melted or damaged wiring or connector from contact with the exhaust, or faulty wiring and connections (both sources). Water getting into the sensor or engine computer connector (OBD-Codes.com). Defective catalytic converter (RepairPal; OBD-Codes.com does not list it). Failed engine computer, which is rare (OBD-Codes.com).

Replace the Bank 1 Sensor 2 oxygen sensor (and the heater fuse if it blew) once wiring and power have been checked (OBD-Codes.com). Repair melted, chafed or water-damaged wiring or connectors (both sources). Replace the catalytic converter if diagnosis shows it is defective (RepairPal). Repair or replace the engine computer only after everything else checks out (OBD-Codes.com).

P0140🌫 Emissions / oxygen sensorsDrive with caution, fix soon

P0140: O2 Sensor No Activity, Bank 1 Sensor 2 (Meaning, Causes, Fixes)

Q: What does P0140 mean?

P0140 means the engine computer sees no activity from the rear (downstream) oxygen sensor on bank 1, the one behind the catalytic converter. Its voltage is stuck near the middle instead of moving up and down. Common causes are a failed sensor or its heater, damaged wiring or connectors, and, according to RepairPal, a defective catalytic converter. The rear oxygen sensor (Sensor 2) sits behind the catalytic converter, and the engine computer uses it to judge how well the converter is cleaning the exhaust. Once hot, the sensor produces a voltage that changes with the oxygen in the exhaust: OBD-Codes.com says lean exhaust gives under about 0.45 volts and rich exhaust gives over 0.45 volts, and that the rear sensor normally switches more slowly than the front one. OBD-Codes.com says P0140 sets when the rear sensor's voltage is stuck between about 0.425 and 0.474 volts, so the computer decides the sensor is inactive. RepairPal defines it the same way: no activity in the signal from the rear oxygen sensor. Bank 1 is the side of the engine with cylinder 1; on four-cylinder engines there is only bank 1. P0160 is the same code for the rear sensor on bank 2, and P0134 is the no-activity code for the front sensor on bank 1.

Q: Can I keep driving with P0140?

Drive with caution, fix soon. Usually drivable for now, but get it checked soon. RepairPal rates P0140 Moderate: not an immediate threat to safety or the car, but it should be diagnosed within a reasonable time. OBD-Codes.com gives no severity rating and says you likely won't notice drivability problems beyond the check engine light, because the rear sensor normally only monitors the catalytic converter. RepairPal notes the car may fail an emissions test.

Reviewed 2026-10-23 · Based on 2 cited source(s)

What P0140 means

The rear oxygen sensor (Sensor 2) sits behind the catalytic converter, and the engine computer uses it to judge how well the converter is cleaning the exhaust. Once hot, the sensor produces a voltage that changes with the oxygen in the exhaust: OBD-Codes.com says lean exhaust gives under about 0.45 volts and rich exhaust gives over 0.45 volts, and that the rear sensor normally switches more slowly than the front one. OBD-Codes.com says P0140 sets when the rear sensor's voltage is stuck between about 0.425 and 0.474 volts, so the computer decides the sensor is inactive. RepairPal defines it the same way: no activity in the signal from the rear oxygen sensor. Bank 1 is the side of the engine with cylinder 1; on four-cylinder engines there is only bank 1. P0160 is the same code for the rear sensor on bank 2, and P0134 is the no-activity code for the front sensor on bank 1.

Severity: can I keep driving?

Drive with caution, fix soon

Usually drivable for now, but get it checked soon. RepairPal rates P0140 Moderate: not an immediate threat to safety or the car, but it should be diagnosed within a reasonable time. OBD-Codes.com gives no severity rating and says you likely won't notice drivability problems beyond the check engine light, because the rear sensor normally only monitors the catalytic converter. RepairPal notes the car may fail an emissions test.

Common symptoms

Check engine light on (both sources)
Often no other noticeable symptoms, since the rear sensor normally doesn't control fueling (both sources; OBD-Codes.com says Chrysler vehicles are an exception)
Failed emissions test in some cases (RepairPal)
Elevated NOx emissions in many cases (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Failed rear oxygen sensor, including a shorted heater circuit inside the sensor, which often also blows the heater fuse (OBD-Codes.com)
Shorted signal circuit in the sensor (OBD-Codes.com)
Melted or damaged wiring or connector from contact with the exhaust, or faulty wiring and connections (both sources)
Water getting into the sensor or engine computer connector (OBD-Codes.com)
Defective catalytic converter (RepairPal; OBD-Codes.com does not list it)
Failed engine computer, which is rare (OBD-Codes.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. If heater codes such as P0141 are also set, deal with the heater circuit and its fuse first.
Warm the engine up and watch the Bank 1 Sensor 2 voltage on a scan tool. OBD-Codes.com says it should switch slowly above and below about 0.45 volts; if it does, the fault is probably intermittent.
If the voltage is stuck, shut the engine off and inspect the sensor's harness and connector for melting, chafing or water, especially where it runs near the exhaust.
With the key on and the sensor unplugged, check for 12 volts at the heater supply and a good heater ground. If the heater fuse is blown, OBD-Codes.com says suspect a shorted heater in the sensor and replace both.
If power, ground and wiring are good, check the remaining circuits against a repair manual for your vehicle before replacing the sensor, and use a high-impedance digital meter.

Typical fixes

Replace the Bank 1 Sensor 2 oxygen sensor (and the heater fuse if it blew) once wiring and power have been checked (OBD-Codes.com)
Repair melted, chafed or water-damaged wiring or connectors (both sources)
Replace the catalytic converter if diagnosis shows it is defective (RepairPal)
Repair or replace the engine computer only after everything else checks out (OBD-Codes.com)

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The sensor, wiring and heater circuit check out but the code comes back
A new sensor didn't fix it; RepairPal warns that the real problem is sometimes the catalytic converter or the wiring
The car failed an emissions test
You also have catalytic converter efficiency codes such as P0420

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0140?

Usually, for a while. RepairPal rates it Moderate, and OBD-Codes.com says you likely won't notice drivability problems because the rear sensor only monitors the catalytic converter on most cars. It can still cause a failed emissions test.

Does P0140 mean I need a new oxygen sensor?

Often, but not always. OBD-Codes.com lists sensor and heater failures plus wiring damage, while RepairPal lists a defective catalytic converter and wiring problems and warns that the sensor is sometimes replaced by mistake. Check the wiring and heater circuit first.

Where is the Bank 1 Sensor 2 oxygen sensor?

It is in the exhaust just behind the catalytic converter on bank 1, the side of the engine with cylinder 1. On four-cylinder engines it is simply the sensor after the converter.

What's the difference between P0140 and P0141?

Both involve the same rear sensor on bank 1. P0140 means its signal shows no activity, and P0141 means a fault in its heater circuit. A bad heater can cause both.

How much does it cost to fix P0140?

Neither source gives a repair cost for P0140. It depends on whether the fix is wiring, a new sensor or a catalytic converter, so get it diagnosed first.

Sources

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.