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DTC codes / BMW codes / P1111

P1111 · BMWEngine Coolant Temperature Radiator Outlet Sensor Low Input

P1111 on BMW vehicles means the engine control module (DME) has detected an abnormally low voltage signal from the radiator outlet coolant temperature sensor, which is the sensor mounted in the lower radiator hose or radiator outlet. The DME expects a voltage within a specific range for the current coolant temperature, and a low input tells it the sensor circuit is shorted to ground or the sensor's internal resistance has dropped out of spec.

SystemPowertrain
Code typeBMW specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Electric radiator fan running continuously or at high speed shortly after startup
  • Coolant temperature gauge reading lower than normal or fluctuating erratically
  • Poor fuel economy or slightly rough running when the engine is cold
  • A stored fault code in the DME with the engine otherwise behaving normally
  • In rare cases, the engine may enter a limited-power mode if the DME substitutes a fixed coolant temperature value

Common causes, most likely first

  1. Radiator outlet coolant temperature sensor internally shorted or failed, pulling the signal voltage low
  2. Chafed or pinched sensor wiring shorting to ground along the lower radiator hose or near the radiator support
  3. Corroded or water-intruded sensor connector causing a low-resistance path to ground
  4. Faulty engine control module (DME) internal pull-up circuit, though this is far less common
  5. Aftermarket or incorrect sensor installed with resistance characteristics outside BMW specifications
  6. Coolant contamination or sensor tip coated with debris altering its resistance curve

How to diagnose and fix it

  1. Scan all modules with a BMW-capable scan tool and record freeze-frame data for P1111, noting coolant temperature and sensor voltage at the time of fault
  2. Visually inspect the radiator outlet sensor connector and wiring for corrosion, chafing, or contact with ground; repair any damaged loom
  3. Measure sensor resistance with a multimeter and compare to BMW's temperature-resistance chart for the current coolant temperature
  4. Back-probe the sensor signal wire at the DME connector and check for a short to ground with the sensor disconnected
  5. If wiring and connector are sound, replace the radiator outlet coolant temperature sensor with a genuine BMW or OEM-equivalent part
  6. Clear the fault memory, run the engine to operating temperature, and verify live data shows a plausible radiator outlet temperature that rises and falls with fan operation
  7. If the code returns with a known-good sensor and verified wiring, perform a guided diagnostic for the DME internal circuit before condemning the control module

Radiator outlet sensor low input traps

  • A low input code does not automatically mean the sensor is bad; a chafed signal wire shorting to ground on the radiator support will set the exact same fault and is a common miss on higher-mileage BMWs.
  • The radiator outlet sensor is often confused with the engine coolant temperature sensor at the cylinder head, but they serve different strategies and only the radiator outlet sensor triggers P1111.
  • When the radiator outlet sensor signal is lost or low, the DME may default the electric fan to a high duty cycle as a failsafe, so a fan that runs constantly is a clue rather than a separate fan fault.
  • Aftermarket sensors with incorrect resistance curves are a frequent cause of repeat P1111 codes even when the connector and wiring test perfectly.
  • Coolant weeping through the sensor connector can create a low-resistance path that only shows up when the engine is hot, so a cold resistance check alone can miss the fault.

Can I keep driving with P1111?

The car is generally safe to drive to a workshop because the DME substitutes a default coolant temperature and runs the fan conservatively, but avoid long trips, heavy loads, or sustained high-speed driving until the fault is repaired. If the temperature gauge climbs above normal or the engine enters limp mode, stop and have the vehicle towed.

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 BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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