P0140

O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

P0140 is a generic OBD-II powertrain diagnostic trouble code: O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2). It is logged by the engine control unit when the o2/lambda monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0140
Group
Powertrain
System
O2/Lambda
Severity
Warning (MIL on)
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What P0140 means

P0140 is an SAE generic powertrain code set when the powertrain control module (PCM) detects no activity from the downstream oxygen sensor on Bank 1, Sensor 2 — the post-catalytic converter sensor on the bank containing cylinder #1. Specifically, the PCM expects the sensor's output voltage to fluctuate in response to changing exhaust conditions; instead, the signal remains static, typically locked between approximately 390–490 mV, or the sensor element fails to reach operating temperature within roughly 60 seconds of engine start.

The Bank 1 Sensor 2 O2 sensor's primary role is to monitor catalytic converter efficiency rather than drive short-term fuel trims. When it stops reporting activity, the PCM cannot confirm that the catalyst is functioning correctly, triggering the MIL. Unlike upstream faults, P0140 rarely causes immediate drivability collapse, but a sluggish or dead downstream sensor can mask catalyst degradation.

The most common root causes are electrical — damaged wiring, corroded connectors, or a heater circuit fault preventing the sensor element from warming up — followed by physical sensor contamination from oil consumption, coolant intrusion, or silicone-based exhaust sealants.

Common causes

Most-frequently reported root causes when P0140 is logged.

  • 1
    Defective or worn-out Bank 1 Sensor 2 oxygen sensor
  • 2
    Damaged, burnt, or corroded wiring/connectors in the sensor circuit
  • 3
    Failed O2 sensor heater element or blown heater circuit fuse
  • 4
    Poor ground connection or low battery/charging system voltage
  • 5
    Sensor contamination from oil consumption, coolant leak, or silicone-based sealants
  • 6
    Vacuum leak causing abnormally lean exhaust conditions
  • 7
    PCM fault (rare — only after all other causes are excluded)

Symptoms drivers notice

Check Engine Light (MIL) illuminated
Slightly increased fuel consumption in some calibrations
Possible failed emissions/MOT test due to catalyst monitoring fault
No immediate drivability change in most cases
Occasional mild hesitation or rough idle if fuel trims are also affected
Black exhaust smoke if sensor failure masks a rich condition

How to diagnose P0140

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all stored codes and freeze frame data; address any upstream O2, misfire, or fuel-trim codes before diagnosing P0140
  2. 2
    Perform a thorough visual inspection of the Bank 1 Sensor 2 wiring harness, connector, and sensor body
  3. 3
    With a multimeter, verify heater circuit voltage and ground integrity; check for a blown fuse on the heater circuit
  4. 4
    Using a scan tool or oscilloscope, monitor live sensor voltage during a warm idle
  5. 5
    Inspect the sensor element for silicone or carbon deposits
  6. 6
    Replace the sensor if wiring, fuses, and grounds test good and the element shows contamination
  7. 7
    Clear codes, perform a complete drive cycle, and confirm the code does not return

Related powertrain codes

Frequently asked questions

Can I drive with a P0140 code?

In most cases yes, short-term. P0140 typically does not cause limp mode or sudden power loss because the downstream sensor does not directly control fuelling on modern engines.

Is P0140 the same as P0136 or P0141?

No. P0136 indicates a general circuit malfunction on Bank 1 Sensor 2, P0141 points specifically to a heater circuit fault, and P0140 means the signal shows no activity.

How much does it cost to fix P0140?

If the fault is a failed sensor, replacement parts typically range from €20–€80, with workshop labour adding €40–€100.

Could P0140 be caused by a catalytic converter problem?

Unlikely as a direct cause. A degraded catalyst does not typically prevent the downstream sensor from generating a signal — it changes the signal pattern instead.

Disabling P0140 in software

RaceTune can permanently disable P0140 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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