Code
P1112
BMW
P — Powertrain
Engine Coolant Temperature Radiator Outlet Sensor High Input
Views:
UK: 33
EN: 58
RU: 60
AI status
Completed
Completed
100%
Causes
- Faulty radiator outlet coolant temperature sensor
- Corroded, loose or damaged sensor connector
- Wiring shorted to battery voltage or other circuit (power feed)
- Open or shorted wiring between sensor and ECU
- Poor ground or loss of reference/pull‑up in the ECU circuit
- Failed engine control module (rare)
Symptoms
- Check Engine Light (MIL) illuminated
- Incorrect coolant temperature reading on scan tool (very high or pegged)
- Poor cold/hot idle or driveability (over‑rich or poor fuel trim)
- Cooling fan operation abnormal (runs constantly or not at correct times)
- Long warm‑up times or revs higher than normal during warm‑up
- Possible engine overheating indications if ECU cannot control cooling system properly
What to check
- Read freeze‑frame and live data for radiator outlet sensor and engine coolant temperature
- Scan for additional codes (thermostat, fan, other temp sensors)
- Visually inspect sensor and connector for corrosion, damage, coolant contamination or loose pins
- Check coolant level and look for air pockets; verify thermostat operation and radiator flow
- Backprobe sensor connector and record voltage and resistance readings with key on and engine at various temps
- Wiggle wiring harness while watching live data to see intermittent changes
Signal parameters
- Typical sensor interface: 0–5 V analog signal to ECU (exact values model dependent)
- High‑input fault usually triggered when sensor voltage is above normal operating range (often >4.5 V) or out of expected bounds for temperature
- ECT type: NTC thermistor (resistance decreases as temperature rises) — expect high resistance at cold, low resistance when hot (exact resistance vs. temperature chart is manufacturer‑specific)
- Measure at sensor connector and at ECU input pin to isolate wiring vs. module issue
Diagnostic algorithm
- Capture freeze‑frame and live data for radiator outlet ECT and engine coolant temp; note conditions when code set.
- Perform visual inspection: sensor, connector, wiring harness routing, and cooling system level/condition.
- Verify actual coolant temperature with independent thermometer/thermocouple or IR gun; compare to scanner reading from the radiator outlet sensor.
- With ignition ON (engine OFF), backprobe sensor connector: measure signal voltage, reference voltage and ground. Record values and compare to expected (consult BMW spec).
- Measure sensor resistance at ambient and after warming (remove sensor if needed) and compare to manufacturer resistance vs. temperature chart. If resistance is out of range, replace sensor.
- If sensor resistance is OK but signal voltage abnormal, check wiring continuity between sensor and ECU and test for shorts to battery (+12 V) or ground. Repair any wiring faults.
- If wiring checks good and new sensor still shows high input, test ECU input circuit or consult BMW resources; consider ECU replacement only after all other causes eliminated.
- Clear codes and test drive to confirm repair; monitor live data for stability.
Likely causes
- Failed radiator outlet ECT sensor
- Damaged connector or pins (corrosion, bent pins)
- Wiring short to B+ or to another high source
- Open or short in wiring harness near sensor (routing damage)
- ECU input circuit fault (last resort)
Fault status
Status
Engine Coolant Temperature (Radiator Outlet) Sensor Circuit — High Input (P1112)
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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