P0140 indicates the powertrain control module (PCM) has detected no activity from the downstream oxygen sensor on bank 1 (sensor 2). This sensor monitors the efficiency of the catalytic converter, and lack of signal suggests a circuit or sensor malfunction rather than converter failure.
The sensor itself may have failed internally, preventing it from generating a voltage signal. This is the most common cause of P0140.
Damaged, corroded, or shorted wiring between the sensor and PCM, or a poor connection at the sensor or PCM harness, can prevent signal transmission.
Leaks upstream of the sensor can introduce extra oxygen, causing erratic or no signal. Leaks downstream can also affect sensor readings.
A blown fuse or faulty relay in the sensor's power or ground circuit can result in no activity being detected by the PCM.
While uncommon, a PCM software glitch or internal fault could incorrectly flag this code. This is a last-resort diagnosis after all other causes are ruled out.
Yes, in most cases, the vehicle will remain drivable. However, the Check Engine Light will stay on, and the vehicle may fail an emissions test. Long-term driving without addressing the issue could lead to reduced fuel economy or catalytic converter damage.
No, P0140 specifically indicates a lack of activity from the downstream oxygen sensor (Bank 1 Sensor 2). The catalytic converter is not directly responsible for this code, though a faulty sensor may prevent proper monitoring of the converter’s efficiency.
Almost never. The PCM is rarely the cause of P0140. The issue is typically with the sensor, wiring, or exhaust system. Only consider PCM replacement after thoroughly ruling out all other potential causes.
If the sensor tests within specifications but the code persists, the issue may lie in intermittent wiring faults, exhaust leaks, or a PCM software issue. Further diagnosis of the wiring harness and connectors is recommended.