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DTC codes / Chrysler codes / P1143

P1143 · ChryslerHO2S Bank 1 Sensor 3 Lean Or Low Voltage

P1143 on a Chrysler vehicle means the powertrain control module has detected that the downstream oxygen sensor on bank 1, sensor 3, is reporting a lean condition or a voltage that stays lower than expected. The computer compares this signal against its internal expectations and flags the circuit when the sensor output remains below the lean threshold for a calibrated period.

SystemPowertrain
Code typeChrysler specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A slight decrease in fuel economy as the PCM adds fuel based on the lean signal
  • Occasional rough idle or hesitation during light acceleration
  • A faint sulfur or rotten egg smell from the exhaust if the engine is running rich
  • Failed emissions inspection due to the stored code and incomplete monitor
  • In rare cases, a surging or fluctuating idle when the sensor signal is erratic

Common causes, most likely first

  1. A failed downstream oxygen sensor (bank 1 sensor 3) that is stuck lean or has an internal short
  2. A damaged or corroded sensor wiring harness or connector causing high resistance
  3. An exhaust leak upstream of the sensor, allowing outside air to skew the reading lean
  4. A leaking fuel injector or low fuel pressure causing an actual lean condition on bank 1
  5. A vacuum leak at the intake manifold or a cracked vacuum hose affecting bank 1
  6. A contaminated sensor from oil or coolant intrusion, often from a failed head gasket
  7. A PCM calibration issue or faulty PCM driver for the sensor heater circuit

How to diagnose and fix it

  1. Connect a scan tool and record freeze-frame data to confirm the code and check for related pending codes
  2. Inspect the bank 1 sensor 3 wiring and connector for chafing, corrosion, or loose pins
  3. Perform a visual check for exhaust leaks around the sensor bung and upstream joints
  4. Use a digital multimeter to check the sensor signal voltage and heater circuit resistance against Chrysler specifications
  5. Smoke-test the intake system to rule out vacuum leaks that would affect bank 1
  6. Replace the downstream oxygen sensor if voltage testing confirms it is stuck lean or unresponsive
  7. Clear the code and complete a drive cycle to verify the repair and ensure the monitor runs to completion

Downstream sensor lean code traps to avoid

  • A lean reading from the downstream sensor often points to an exhaust leak before the sensor rather than a failed sensor, so always inspect the exhaust system first.
  • Chrysler downstream sensors can be contaminated by silicone from improper sealants or coolant from a failing head gasket, which mimics an electrical failure.
  • The PCM may set P1143 even when the sensor is functioning correctly if the upstream sensor is lazy and the fuel trim is skewed, so check fuel trim data before condemning the downstream sensor.
  • A faulty thermostat that keeps the engine running cold can cause a lean downstream reading because the PCM stays in open-loop fuel control longer than expected.
  • Replacing the sensor without addressing a vacuum leak or low fuel pressure will often result in the code returning within a few drive cycles.

Can I keep driving with P1143?

You can usually continue driving with P1143, but avoid heavy acceleration or towing until the fault is repaired because a persistent lean condition can raise exhaust temperatures and damage the catalytic converter over time. Have the vehicle diagnosed promptly to prevent secondary damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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