B1390

Code

FIAT B — Body

Oil temperature sensor short to ground

Brand: FIAT

Type: B — Body

Views: UK: 21 EN: 40 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Damaged or chafed wiring harness with conductor contacting chassis ground
Shorted or corroded connector (water ingress, pin pushed out)
Failed oil temperature sensor internal short to ground
Aftermarket or incorrect replacement sensor with wrong characteristics
Faulty ECM input driver (rare)
Improperly routed harness contacting hot/grounding body panels or engine components

Oil temperature gauge reading abnormally low or pegged at minimum
Instrument cluster or engine warning lamp or message displayed
ECM uses default/fallback oil temperature value — possible altered engine control or emissions strategy
Stored trouble code B1390 and possible reduced diagnostic confidence for related systems
No engine cranking issues in most cases (sensor-specific)

Read and record freeze-frame and pending data with a compatible scan tool; note oil temperature and related parameters
Visual inspection of sensor, connector, and wiring for damage, corrosion, pin push-out, or signs of heat/oil contamination
Check continuity between sensor signal pin and chassis ground with ignition off (expect open — a direct short indicates fault)
Backprobe sensor connector with ignition on to measure signal/reference voltages per service manual
Wiggle test wiring and connector while monitoring signal for intermittent faults
Inspect routing for harness chafe points where wire could be grounded to engine or body

Typical thermistor-type oil temp sensor: resistance varies with temperature — verify values in vehicle service manual
Expected sensor signal voltage typically within ~0.5–4.5 V depending on design; a voltage ~0 V or steady near ground indicates a short-to-ground
Open-circuit or very high resistance (>10 kΩ) indicates open; very low resistance (~0–10 Ω) suggests a short to ground
Always compare to FIAT factory specifications for exact voltage/resistance vs temperature curves

Verify code with a scan tool and review freeze-frame data; note operating conditions when code set.
Visually inspect oil temperature sensor, connector, and harness for damage, oil contamination, or corrosion.
With ignition off, disconnect sensor and measure continuity between the sensor signal terminal and chassis ground. If near 0 Ω, wiring is shorted to ground.
Reconnect and backprobe the sensor with ignition ON (engine off). Measure reference voltage and signal voltage at the ECU connector and at the sensor — compare to factory specs.
If signal is at ground at the ECU connector, isolate by disconnecting the harness at intermediate connectors and retest to locate short segment.
If the sensor itself measures as near shorted (very low resistance to ground), replace the sensor and retest.
Repair any damaged wiring or connector (replace pigtail or repair with solder and heat-shrink or approved crimp repair), reseal connectors, and secure harness away from chafe points.
Clear codes, perform a test drive or run warm-up cycle to verify the code does not return and that oil temperature readings are plausible.

⚠️ Status

Oil temperature sensor circuit short to ground — B1390. Sensor signal reading at or near ground; inspect sensor, wiring, and connectors.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

Repair manuals

Manual library for FIAT

Browse 26 FIAT manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

Your experience will help others

+100 karma for a short comment :)

Was this AI description helpful?

Your feedback helps improve AI descriptions.

👍 Like 0 👎 Dislike 0

Send to email