P0145: O2 Sensor Circuit Slow Response (Bank 1, Sensor 3)
Quick Answer
Safe to drive (short-term)
P0145 means the third oxygen sensor on Bank 1, fitted after a second (usually under-floor) catalytic converter, is not switching between rich and lean readings quickly enough during the ECU's monitor test. Only a minority of petrol cars built to the strictest emissions standards have a Sensor 3, so this code applies to specific exhaust layouts.
- Severity
- Moderate · Emissions
- Estimated repair cost
- From €55 to €380+, varies by vehicle
€55 or €380, depending on your car.
- Repair sensor wiring or connector€55–€160
- Replace Bank 1 Sensor 3€110–€380
A scan shows whether P0145 is really stored on your car, which codes sit next to it and how urgent each one is.
A scan needs a Bluetooth OBD2 adapter (Bluetooth LE on iPhone), about €25-60; the built-in demo runs without one. See which adapter to buy
What does P0145 mean?
P0145 is a emissions-related diagnostic trouble code classified as moderate severity.
Where it is on the car
- Engine
- Oxygen sensor before the converter (sensor 1)
- Catalytic converter
- Oxygen sensor after the converter (sensor 2, or 3 on some cars)
- Silencer and tailpipe
What are the symptoms of P0145?
- Check engine light illuminated
- Slight reduction in fuel economy
- Possible failed emissions test
- No noticeable driveability symptoms
- May appear with P0420 if the aftertreatment is also degrading
What causes P0145?
Aged Bank 1 Sensor 3 with degraded response time
: high
Contaminated sensor element (oil, coolant, silicone, AdBlue residue)
: high
Exhaust leak near the sensor distorting the gas sample
: medium
Damaged sensor wiring causing intermittent signal loss
: low
Failing secondary catalyst reducing reference gas stability
: low
Is it safe to drive with P0145?
Generally yes, for short-term driving. Safe to drive short term. Sensor 3 only monitors the second catalytic converter and does not control the fuel mixture, so a slow sensor mainly means a developing converter problem may be masked. Plan a repair within a few weeks to keep emissions diagnostics working properly.
How do you diagnose P0145?
- Confirm the vehicle's exhaust layout. Sensor 3 is only present on cars with a third oxygen sensor after a second catalytic converter
- Read freeze frame data and look for companion codes (P0420, P0143) that suggest a broader aftertreatment issue
- Inspect the exhaust system around Sensor 3 for leaks that could distort the gas sample
- Use a scan tool to graph Sensor 3 voltage during steady cruise and deceleration fuel cut. A healthy sensor reacts within roughly 100 ms to a lean spike when fuel is cut
- Substitute a known-good sensor. Response time is the only definitive test, so if the new sensor responds correctly, the original was aged out
How much does P0145 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace Bank 1 Sensor 3 | €50–€220 | €60–€160 | €110–€380 | Moderate |
| Fix exhaust leak near Sensor 3 | €20–€120 | €70–€220 | €90–€340 | Moderate |
| Repair sensor wiring or connector | €5–€30 | €50–€130 | €55–€160 | Moderate |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
Common questions about P0145
- What does slow response mean for an O2 sensor?
- It means the sensor element no longer changes voltage quickly enough when the exhaust gas composition shifts. The ECU times the sensor's response during specific monitor tests and sets P0145 when it falls below the required threshold.
- Why does my car have three O2 sensors per bank?
- Most cars do not. Some petrol cars built to the strictest emissions standards have a second catalytic converter further down the exhaust, with a third oxygen sensor after it to monitor it. On diesels, the sensors after the SCR catalyst are NOx sensors, which report their own fault codes rather than P0145.
- Can I clean a slow O2 sensor instead of replacing it?
- No, not reliably. The platinum and ceramic element is consumed over time and cannot be restored by chemical cleaning. Cleaning may briefly improve readings but the failure will return within weeks. Replacement is the only durable fix.
- Will P0145 trigger limp mode?
- No. P0145 is an emissions monitoring code and does not by itself force limp mode. Sensor 3 does not control the fuel mixture, so the engine keeps running normally on its upstream sensors.