B1298

Code

FIAT B — Body

Volumetric anti-theft sensor supply short to positive

Brand: FIAT

Type: B — Body

Views: UK: 6 EN: 6 RU: 5

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Page language: EN

Interior motion sensor (volumetric) alarm triggers incorrectly or not at all
Alarm may arm/disarm incorrectly or fault indicator/warning lamp on instrument cluster
Stored B1298 and possibly related body/BCM codes in scan tool
Intermittent or permanent loss of alarm/immobilizer functionality
Vehicle may fail security checks on startup (immobilizer related symptoms)

Read and record all stored DTCs and freeze frame data with a scan tool; note ignition/key state when fault set
Visually inspect interior (headliner/pillars) harness routing and sensor location for chafing, water damage or pinched sections
Inspect volumetric sensor connector for corrosion, bent pins, push‑outs or contamination
Check fuse(s) and relay(s) protecting the sensor supply; verify correct fuse rating and seating
Disconnect volumetric sensor connector and check if DTC clears after key cycles (helps isolate sensor vs. harness/BCM)
Back‑probe sensor supply circuit with ignition ON and measure voltage with sensor connected and disconnected

Expected supply voltage: battery voltage present at fused/switched sensor feed when supply is intended to be powered (~11–14.5 V) — confirm in factory manual for exact circuit behavior
When sensor is disconnected, the harness supply feed should not show a direct short to ignition-switched battery positive or unintended permanent positive (verify with multimeter)
Resistance from supply wire to chassis ground should be high (open) when circuit is healthy; a low resistance to positive indicates short
Compare readings to vehicle wiring diagram and factory specified voltages/circuit locations

Connect a scan tool, read/record codes, clear codes and perform a key cycle to see if B1298 returns and under what conditions.
Perform a careful visual inspection along the harness from the sensor to the BCM/fusebox; remove trim required to expose wiring runs.
Verify fuses and relays for the sensor circuit; replace if suspect and retest.
With ignition ON, back‑probe the sensor connector supply pin. Note voltage with sensor connected and then with sensor disconnected. If supply is present when it should be off, consult wiring diagram for switched feed/relay wiring.
With battery disconnected, use an ohmmeter to check for continuity between the supply wire and battery positive. Low resistance suggests a short to positive in wiring or connected module.
Isolate the short by unplugging intermediate connectors or removing sections of harness; repeat measurements to locate the section with the short.
Inspect and/or replace the volumetric sensor only after harness and connector integrity are confirmed. Reconnect and clear codes.
If wiring and sensor check good, consider BCM/module bench testing or replacement per factory procedure; verify for software updates or documented service bulletins.
After repair, clear codes, verify alarm/immobilizer operation and road/occupancy tests where applicable.

Chafed wiring where harness contacts metal body or another positive feed
Water ingress/corrosion in sensor connector or junction block
Aftermarket alarm/remote start incorrectly wired into sensor supply
Sensor internal failure creating a direct short to battery positive
Loose/incorrectly assembled connector pin causing contact with positive terminal

⚠️ Status

Volumetric anti-theft sensor supply circuit shorted to positive — inspect sensor, harness, connectors and module for short to battery positive.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2 hours

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