Code P0140: Meaning and Causes
The P0140 error code is a generic powertrain code (OBD-II) that indicates no activity detected in the oxygen sensor (O2) circuit located downstream of the catalytic converter, on Bank 1 (B1S2).
The Powertrain Control Module (PCM) sends a reference voltage of 0.45 volts to the sensor. Once hot, the sensor generates a variable voltage based on the oxygen content in the exhaust gases: a low voltage (< 0.45 V) indicates a lean mixture, a high voltage (> 0.45 V) a rich mixture.
The rear sensor (S2) is used only to monitor the efficiency of the catalytic converter (TWC). If the PCM receives a “stuck” and inactive signal (constant voltage between 0.425 V and 0.474 V), it records the P0140 code.
Symptoms of Code P0140
- Malfunction Indicator Lamp (MIL) illuminated.
- Generally no noticeable driving issues are felt, as this sensor does not affect the air-fuel mixture (except on some Chrysler models).
- Likely failure of the emissions test (technical inspection).
Possible Causes of the Fault
The causes of a P0140 code are limited and often related to the electrical circuit:
- Short circuit in the heater circuit or signal circuit of the O2 sensor.
- Blown fuse in the heater circuit.
- Melted or damaged wiring harness or electrical connector (often due to contact with the exhaust).
- Moisture intrusion or corrosion in a connector or at the PCM.
- Failed O2 sensor Bank 1 Sensor 2.
- Internal PCM failure (less common).
Diagnosis and Solutions for Resolving P0140
Here is a step-by-step diagnostic procedure to identify and resolve the cause of the P0140 code.
1. Test with the Diagnostic Tool
Start the engine and let it reach operating temperature. Using an OBD2 diagnostic tool, observe the live data voltage of the B1S2 sensor. A voltage that slowly oscillates around 0.45 V indicates an intermittent problem. If the voltage is stuck, continue the diagnosis.
2. Visual Inspection
With the engine cold, visually inspect the wiring harness and connector of the B1S2 sensor. Look for signs of burning, chafing, or heat damage. Also check the condition of the wiring up to the PCM. Repair or replace any damaged components.
3. Heater Circuit Check
Turn the ignition on (without starting the engine). Disconnect the O2 sensor connector. Using a multimeter, check for the presence of 12V at the heater circuit supply pin and a good ground.
- No 12V? Check and replace the corresponding fuse. If the fuse blows again, the problem is most likely a short circuit in the O2 sensor heater.
- Ground issue? Clean or repair the ground connection point.
4. Signal Circuit Check (5V Reference)
Still with the connector disconnected, check for the presence of a reference voltage of approximately 5V on the signal wire at the connector.
- No 5V? Check this voltage directly at the PCM connector.
- If the 5V voltage is absent at the PCM, the PCM is likely faulty.
- If the voltage is present at the PCM but not at the sensor connector, there is an open or short circuit in the wiring.
- Chrysler Note: A short circuit on any sensor using the 5V reference can cause this problem. Disconnect the sensors one by one until the 5V reappears to identify the faulty component.
5. O2 Sensor Replacement
If all voltages and grounds are correct, the Bank 1 Sensor 2 oxygen sensor is most likely defective. Replace it with a quality part, clear the codes, and perform a road test to confirm the repair.
Conclusion and Call to Action
The P0140 code is often simple to diagnose and resolve by following a logical procedure. Although it generally does not affect vehicle performance, it must be corrected to ensure proper operation of the emissions system and to pass the technical inspection.
Need help diagnosing or replacing your O2 sensor? Consult a certified mechanic for professional diagnosis and reliable repair.