P1145

Code

CHEVROLET P — Powertrain

HO2S Cross Counts Bank 1 Sensor 3

Brand: CHEVROLET

Type: P — Powertrain

Views: UK: 29 EN: 63 RU: 28

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Page language: EN

Causes

Failing or contaminated oxygen sensor (HO2S)
Open/short or intermittent wiring and poor connector/ground at the sensor
Exhaust leak upstream of the sensor or near the bank being monitored
Rich/lean fuel mixture (fuel pressure, injector, control issues)
Catalytic converter deterioration or internal damage
PCM or reference voltage issue (rare)

Symptoms

Check Engine Light (MIL) ON
Failed or marginal vehicle emissions test
Illogical or fluctuating fuel trim values on live data
Occasional rough idle or hesitation if combustion issues present
Possible reduced fuel economy

What to check

Read and record all stored/pending codes and freeze‑frame data with a scan tool
Identify which physical sensor is Bank 1 Sensor 3 on the specific vehicle/engine
Perform a visual inspection of the sensor, connector and wiring for damage, corrosion, contamination or exhaust soot
Check for exhaust leaks upstream of the sensor (sniffing, smoke test or visual)
Monitor live O2 sensor voltages and fuel trims with a scan tool while warming to operating temperature and during a drive cycle
Compare upstream (pre‑cat) and downstream (post‑cat) O2 sensor behavior

Signal parameters

Typical oxygen sensor switching threshold ~0.45 V (varies by calibration)
Upstream (pre‑cat) narrowband O2: ~0.1–0.9 V switching frequently (several times per second) when closed‑loop
Downstream (post‑cat) O2: usually steadier around ~0.45 V with few crossings; excessive crossings indicate fault
Cross count trigger: depends on OEM calibration but commonly problems flagged when cross counts exceed a low double‑digit number during a drive cycle (example: >10–20 crosses)
Heater circuit: resistance and supply voltage vary by sensor/vehicle — normal heater resistance often in low single‑digit ohms to low tens of ohms and should have battery voltage present on the supply pin with ignition on (specific values in OEM data)

Diagnostic algorithm

Connect a professional scan tool and read all DTCs; record freeze frame and fuel trim data
Verify sensor identity and location for Bank 1 Sensor 3 on the specific Chevy model
Visually inspect sensor and harness for damage, oil/coolant contamination, corrosion or loose connector; repair as needed
Check for exhaust leaks upstream of the sensor (use smoke machine or pressure test) and fix any leaks
With a scan tool, monitor HO2S Bank1 Sensor3 voltage and count crossings vs time. Compare to upstream sensor to determine if switching is genuine or sensor‑specific
Check sensor heater: measure supply voltage with key on and resistance to ground per OEM; verify heater operation (heater on should warm and allow normal operation)
Perform a wiggle test on wiring/connectors while observing live data for intermittent faults
Check fuel system: fuel pressure, injector function and short/long term fuel trims; address any open loop, high fuel pressure or injector issues
Check for misfires (scan for misfire codes, inspect ignition components and compression if needed)
If wiring and vehicle systems check good and downstream waveform remains unstable, replace Bank 1 Sensor 3 with OE‑equivalent sensor
After repair, clear codes and perform a full drive cycle to verify the code does not return and that fuel trims and O2 traces are normal

Likely causes

Faulty Bank 1 Sensor 3 (post‑cat)
Damaged/poor connector or wiring to Sensor 3
Exhaust leak between head and sensor or at manifold/collector
Fuel trim or misfire causing unstable oxygen content

Fault status

⚠️ Status

MIL illuminated. DTC P1145 stored: HO2S cross counts exceed limit for Bank 1 Sensor 3. Freeze frame and live data recommended for diagnosis.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 to 3.0 hours

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P1145 — HO2S Cross Counts Bank 1 Sensor 3