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GTECH Calibration
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P1157

HO2S Bank 2 Sensor 2 Lean System Or Low Voltage.

  • Saturn
  • Powertrain
  • Manufacturer code
  • Low severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
1
AreaFuel and air metering
57
FaultThe specific fault in that area

What it means

On a Saturn, P1157 means the post-catalyst heated oxygen sensor on bank 2 (sensor 2) is reporting a lean condition or a voltage that stays too low. The engine control unit saw the downstream sensor signal sit low and fail to switch as expected while the engine was running in closed loop. It can point to a sensor, wiring or exhaust leak fault, or to a genuine fuel or air problem on that bank.

Symptoms

  • Check engine light on
  • Usually no obvious change in driveability
  • Possible slight rise in fuel consumption
  • Other fuel trim or oxygen sensor codes stored alongside
  • Failed emissions test
  • Rough running or hesitation if a real lean condition exists

Possible causes

  • Faulty or aged bank 2 downstream oxygen sensor reading lowlikely
  • Damaged wiring, chafed signal wire or corroded connector at the bank 2 sensor 2 circuitlikely
  • Exhaust leak near the sensor or upstream of it letting in extra airpossible
  • Genuine lean running on bank 2 from a vacuum leak, low fuel pressure or a dirty or faulty injectorpossible
  • Sensor heater circuit fault leaving the sensor slow to reach working temperaturepossible
  • Fault in the engine control unit or its sensor reference circuitrare

How to diagnose

  1. Read all stored and pending codes and the freeze frame data, noting engine temperature, load and fuel trim values when the code set
  2. Confirm which side is bank 2 for this Saturn model and engine, as layout varies
  3. Inspect the sensor wiring and connector for chafing, heat damage, water ingress and corrosion
  4. Check the exhaust for leaks around the manifold, flex joints and the catalyst area
  5. Look at short and long term fuel trims on both banks to see if bank 2 is genuinely lean
  6. Check for vacuum leaks and test fuel pressure if trims show a lean condition
  7. Watch the live downstream sensor voltage at operating temperature and during a snap throttle test to see if it responds
  8. Check the sensor heater circuit supply, ground and resistance against the manufacturer's specification

How to fix

  • Repair or replace damaged wiring and connectors on the sensor circuit
  • Replace the bank 2 downstream oxygen sensor if it is slow, stuck low or fails its tests
  • Repair any exhaust leak and renew faulty gaskets or joints
  • Fix vacuum leaks or intake air leaks that cause bank 2 to run lean
  • Correct fuel delivery faults such as low pressure or a faulty injector
  • Clear the codes after repair and road test to confirm the fault does not return

Can I keep driving?

Low severity

The car can normally be driven while you book it in, as the downstream sensor mainly monitors catalyst efficiency. If it is running roughly or hesitating, which suggests a real lean condition, get it checked sooner to avoid engine or catalyst damage.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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