OBD codes / P0142
P0142
ModerateO2 Sensor Circuit Malfunction (Bank 1, Sensor 3)
This is a monitoring-only sensor, so P0142 changes nothing about how the car drives. Handle it as an emissions-compliance repair on your own schedule — before an inspection, and before relying on any catalyst-related diagnosis, since the computer uses this sensor to grade the second converter.
What this code means
Sensor 3 is the third oxygen sensor in line on Bank 1 — it only exists on vehicles with two catalytic converters in series on that side, where it sits after the second converter to monitor the overall cleanup of the exhaust. Many cars do not have a Sensor 3 at all, so this code appears only on those that do. P0142 is the general circuit fault for that sensor: its signal is out of range, erratic, or unusable. Like any post-catalyst sensor, it monitors rather than controls, so a fault here does not change how the engine runs. The likely causes are the usual trio — a worn sensor, wiring or connector damage (this sensor sits far back along the underbody, exposed to road spray and debris), or an exhaust leak near it.
Symptoms you might notice
- Check-engine light with no drivability symptoms
- Failed emissions test
- No change in fuel economy or performance
What it costs to fix
Typical range: $100–$450 · about ~0.3–1 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Oxygen (O2) sensor (post-catalyst, sensor 3) | $30–$250 | ~0.3–1 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
| Exhaust leak repair near the sensor | $20–$200 | ~0.5–2 hrs |
Sensor 3 usually sits under the floor where access is easy, keeping labor short — unless rust has welded it into the pipe. On rust-prone cars, a seized sensor or a crumbling exhaust bung is the wildcard.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0142 for my exact vehicle →
Frequently asked
My car has three O2 sensors on one bank?
Only some do. Sensor 3 exists on vehicles with two catalytic converters in a row on that bank — it sits after the second one. If you see P0142, your car is one of them; many cars top out at two sensors per bank.
Does P0142 affect performance or fuel economy?
No. Fuel control comes from Sensor 1 up front; Sensor 3 just monitors the tail end of the emissions cleanup. The check-engine light is normally the only symptom you will ever notice.
Can I drive with P0142?
Yes, freely — it has no effect on engine operation. Just plan the fix before an emissions test, where any active check-engine light is a fail.
What is the likely fix for P0142?
Most often the sensor itself, but because this one lives far back under the car, damaged wiring and corroded connectors are close behind. A visual inspection of the harness is a smart first step before parts.
Seeing P0142 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0142 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.