B1387

Code

FIAT B — Body

Oil temperature sensor open or short to positive

Brand: FIAT

Type: B — Body

Views: UK: 2 EN: 4 RU: 6

AI status

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Page language: EN

MIL/Check Engine lamp illuminated
Oil temperature gauge or display stuck, reading extreme or implausible value
Engine control using incorrect oil temperature for strategy — possible rough idle, increased warm-up enrichment or fuel trim changes
Possible limp-home mode or degraded engine performance in some vehicles

Read stored freeze frame and live data for oil temperature and related parameters
Scan tool: confirm B1387 is current or historical and note other related codes
Visually inspect sensor, connector and wiring harness for damage, corrosion, oil contamination or loose terminals
Back-probe sensor connector and read sensor voltage with ignition ON (engine OFF) using a multimeter/scan tool
Measure sensor resistance at the sensor plug with sensor removed (compare to OEM specification)
Check continuity between sensor connector and ECU pin and measure for short to battery positive (B+)

Sensor type: typically thermistor (NTC) — resistance changes with temperature
Typical interface: ECU monitors voltage on sensor circuit; sensor resistance forms a voltage divider with ECU pull-up/pull-down (0–5 V domain)
Fault indications: open circuit or short to positive typically yields a constant/high voltage reading at the ECU sensor input
Expected behaviour: resistance decreases as temperature increases (NTC). Consult OEM spec for exact resistance/voltage values at known temperatures

Confirm code and note freeze-frame/live data; check for related fault codes (ECU, ground faults).
Visually inspect oil temperature sensor, connector, harness and nearby areas for mechanical damage, oil contamination or corrosion. Repair visible damage.
With ignition ON (engine OFF), back-probe the sensor connector: measure voltage at the sensor signal pin. A steady battery voltage or near-B+ suggests short to positive or open with pull-up; near 0 V may indicate short to ground. Record values.
Disconnect sensor and measure resistance across sensor terminals at ambient temperature. Compare to OEM resistance/temperature chart. Infinite or very high resistance = open; very low resistance = short. If sensor out of spec, replace sensor.
Check continuity between the sensor connector and the ECU pin. Also check for unintended continuity to battery positive (B+) and to ground. Repair wiring or connector faults as required.
If wiring and sensor are good, inspect the ECU connector and ground points; measure input at ECU pin with connector connected to verify expected signal. Replace/repair ECU only after exhausting wiring/sensor checks and consulting OEM guidance.
After repairs or sensor replacement, clear codes and perform functional test: run engine to bring oil to operating temperature while monitoring oil temperature live data and confirm code does not return.

Damaged insulation rubbing through to B+ causing intermittent short
Connector pins pushed out, corroded or filled with oil causing open/poor contact
Burnt or melted wiring near the sensor from heat or contact
Sensor element failure (open thermistor or internal short)

⚠️ Status

Oil temperature sensor circuit fault — open or short to positive (B1387). ECU detects invalid/high signal from oil temperature sensor.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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