OBD codes / P0145
P0145
ModerateO2 Sensor Circuit Slow Response (Bank 1, Sensor 3)
Drive without worry — a slow third-row sensor affects nothing you can feel from the driver's seat. Replace it when convenient, prioritizing before an emissions inspection or before anyone diagnoses a catalyst code on this bank, since this sensor's data feeds that judgment.
What this code means
This code means the third oxygen sensor on Bank 1 — present only on vehicles with a second, downstream catalytic converter — took too long to react when the computer tested it. The computer occasionally provokes a mixture change (often during deceleration fuel cut) and times how quickly each sensor responds; a healthy element registers the swing promptly, while an aging one lags. Slow response is the classic signature of a sensor wearing out, with contamination from oil, coolant, or silicone vapors as the other common cause; marginal wiring or an exhaust leak near the sensor can also smear the reading. Since Sensor 3 only verifies the final stage of emissions cleanup, nothing changes in how the car drives — this is an emissions-integrity fault, not a performance one.
Symptoms you might notice
- Check-engine light with no other noticeable symptom
- Failed emissions test
- No performance or economy change
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 |
| Exhaust leak repair near the sensor | $20–$200 | ~0.5–2 hrs |
A lazy sensor is replaced, not repaired, and this position is usually easy to reach under the floor — expect the low end unless rust has seized it. If contamination is suspected, find and fix the oil or coolant source or the new sensor will slow down too.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0145 for my exact vehicle →
Frequently asked
What does 'slow response' mean for an O2 sensor?
The computer times how fast the sensor reacts to a deliberate mixture change. A response slower than spec means the sensing element has aged or been contaminated — the automotive equivalent of a worn-out battery that still works, just badly.
Is P0145 worth fixing if the car drives fine?
Yes, eventually. The car will always drive fine with this fault — that is the nature of post-catalyst sensors — but you cannot pass an OBD emissions test with an active code, and the catalyst monitor on this bank is unreliable until the sensor responds properly.
What is the usual cause of P0145?
Plain old age — sensor elements slow down over tens of thousands of miles. Contamination from burning oil or coolant is the main alternative, and it matters because a contaminated replacement will fail the same way unless the source is fixed.
How does P0145 differ from P0133 and P0139?
All three are slow-response faults on Bank 1, just at different positions: P0133 is Sensor 1 (upstream, affects fuel control), P0139 is Sensor 2 (after the first converter), and P0145 is Sensor 3 (after the second converter, on cars that have one).
Seeing P0145 on your car? Get a diagnosis specific to your exact year, make and model.
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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.