P1145

Code

CHRYSLER P — Powertrain

HO2S Cross Counts Bank 1 Sensor 3

Brand: CHRYSLER

Type: P — Powertrain

Views: UK: 35 EN: 55 RU: 30

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Page language: EN

Causes

Faulty Bank 1 Sensor 3 oxygen sensor (contaminated, worn, or internally shorted)
Damaged/poor wiring or connector (open, short to power/ground, high resistance) to sensor or heater circuit
Exhaust leak upstream of the sensor allowing additional oxygen into the signal stream
Failing catalytic converter (reduced conversion efficiency causing downstream sensor to switch)
Engine mechanical or fuel issues causing intermittent rich/lean conditions (misfire, leaking injector, low/high fuel pressure, vacuum leak)
PCM software or internal fault (rare)

Symptoms

Check Engine Light (MIL) illuminated with P1145 stored
Unexpected fuel trim changes or drivability symptoms if underlying problem severe
Downstream O2 sensor (Bank1 Sensor3) shows excessive switching when monitored in live data
Possible poor fuel economy if exhaust/combustion issues present

What to check

Read and record freeze frame and all stored codes; check for related codes (misfire, fuel trim, catalyst, other O2 sensors)
Monitor live data: HO2S Bank1 Sensor3 voltage and switching behavior, compare with Bank1 Sensor1 (upstream)
Inspect sensor harness and connector for corrosion, burnt pins, damage, or pinched wires
Backprobe sensor connector to verify heater supply and ground (typically battery voltage to heater and a switched ground)
Check for exhaust leaks between head/manifold and sensor or around catalytic converter
Check fuel pressure and for misfires/vacuum leaks if upstream O2 sensor shows instability

Signal parameters

Typical zirconia O2 voltage range ~0.1–0.9 V for switching sensors; upstream sensor will switch frequently, downstream (post-catalyst) should be relatively steady with few crossings
‘Cross counts’ = number of threshold crossings in a defined time window; P1145 indicates counts outside expected range for Bank1 Sensor3
Heater circuit should show near-battery voltage on supply and low resistance to ground when commanded; heater resistance spec varies by sensor (consult service data)

Diagnostic algorithm

Retrieve all codes and freeze-frame data. Note any related codes (misfire, fuel trim, catalyst codes).
Use a scan tool to view live data for HO2S Bank1 Sensor1 and Sensor3 during warm idle and a short drive. Compare switching patterns — if Sensor3 mirrors Sensor1 switching, suspect catalytic inefficiency or sensor issue.
Visually inspect sensor and wiring harness for damage, corrosion, rodent chew, loose or corroded connector pins. Repair as needed.
Verify heater circuit: with connector disconnected measure heater resistance and apply power to verify current draw (or activate heater via scan tool). Replace sensor if heater open or out of spec.
Backprobe signal lead with oscilloscope or graphing scan tool while inducing rich/lean conditions (brief propane or smoke test for intake) to confirm sensor response. Downstream sensor should not switch rapidly if catalyst is good.
Check for exhaust leaks upstream of sensor and repair if present. Verify catalytic converter temperature differential (infrared gun): upstream should be hotter than downstream when active; little difference may indicate failed cat.
Check for engine issues causing abnormal O2 behavior: scan for misfires, inspect fuel pressure, check for vacuum leaks, and repair as needed.
If wiring, heater, and engine are good but Sensor3 still shows abnormal cross counts, replace the oxygen sensor. After repairs clear codes and perform a full drive cycle to confirm the fault does not return.
If fault persists after new sensor and wiring confirmed, consider catalytic converter efficiency test and PCM/ECM diagnosis per factory procedures.

Likely causes

Aging or contaminated Bank 1 Sensor 3 showing excessive switching
Damaged sensor harness or corroded connector causing intermittent signal
Catalyst efficiency reduced causing downstream sensor to follow upstream switching
Exhaust leak between catalytic converter and sensor allowing false readings

Fault status

⚠️ Status

HO2S Cross Counts — Bank 1 Sensor 3. Downstream oxygen sensor switching count out of expected range; indicates sensor response, wiring/heater, catalytic converter, or upstream engine/fuel issue.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.5 hours

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P1145 — HO2S Cross Counts Bank 1 Sensor 3