P0145

Code

Generic P — Powertrain

O2 Sensor Circuit Slow Response Bank 1 Sensor 3

Brand: Generic

Type: P — Powertrain

Views: UK: 35 EN: 27 RU: 29

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Page language: EN

Causes

Aging or contaminated O2 sensor (sensor degradation)
Contaminants on sensing element (oil, coolant, silicone, fuel additives)
Damaged or corroded wiring or connectors in the sensor circuit
Poor sensor heater operation or slow warm-up
Exhaust leak upstream of the sensor
Faulty catalytic converter reducing expected oxygen change

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Possible failed emissions test
Reduced fuel economy (sometimes)
Possible rough idle or drivability issues (less common for downstream sensor codes)
Incomplete or failed catalyst monitoring readiness

What to check

Read and record freeze frame and related codes; note readiness status
Visual inspection of sensor wiring, connectors and harness for damage or corrosion
Check for exhaust leaks near sensor and upstream areas
Verify proper power/ground to sensor heater and signal circuit at connector
Compare sensor voltage/waveform to upstream sensor using a scan tool or oscilloscope
Measure heater resistance against manufacturer spec

Signal parameters

Narrowband O2 sensor typical voltage range: ~0.1–0.9 V (varies by vehicle)
Upstream (pre-cat) sensor should switch rapidly between low and high voltages during closed-loop
Downstream (post-cat) sensor often shows more stable voltage near mid-level when catalyst is good, but should still reflect changes with upstream; slow response means delayed or damped change compared with upstream
Heater circuit should show continuity and be powered to reach operating temperature quickly (exact resistance/voltage varies by manufacturer)

Diagnostic algorithm

Confirm code and check for other related O2 or catalyst codes (note freeze frame).
Perform a visual inspection: sensor, connector, wiring harness for damage, contamination, or corrosion; repair obvious issues.
Check for exhaust leaks and repair if present.
Backprobe sensor connector and verify heater power and ground with ignition on; measure heater resistance and compare to spec.
Using a scan tool or lab scope, monitor Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 3 signals simultaneously during warm idle and during commanded fuel changes. Look for delayed or muted response on Sensor 3 relative to Sensor 1.
If sensor heater is not functioning or sensor signal is out of expected range, replace the sensor. If wiring/power/ground problems are found, repair wiring and retest.
If sensor and wiring check good but downstream response remains abnormal, inspect catalytic converter efficiency (temperature probes, backpressure, or downstream vs upstream readings); replace catalyst if confirmed failing.
Clear codes and perform drive cycle to verify repair and readiness.

Likely causes

Failed or aged downstream oxygen sensor
Open/short or high resistance in signal/ground wiring or connector
Heater circuit not reaching operating temperature
Exhaust leak near upstream sensor or near sensor mounting
Catalyst inefficiency or internal damage

Fault status

⚠️ Status

O2 Sensor Circuit Slow Response — Bank 1 Sensor 3. The downstream oxygen sensor is not responding at the expected rate, indicating a slow or delayed signal.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours