B1451

Code

OPEL B — Body

Accessory Relay Circuit High Voltage or Open Circuit

Brand: OPEL

Type: B — Body

Views: UK: 6 EN: 10 RU: 4

AI status

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Page language: EN

Causes

Blown or poor fuse for accessory circuit
Faulty accessory relay (stuck open, internal short)
Open or corroded wiring/connector in relay control or supply circuit
Poor or intermittent ground for relay/BCM
Faulty BCM or relay driver transistor
Aftermarket accessory or recent repair damaged wiring

Symptoms

Accessory items (radio, cigarette lighter, power outlets, interior modules) not powered or intermittent
Related convenience functions may not operate or are erratic
DTC stored and possibly related warning lights on instrument cluster
No crank or strange behavior only when accessories are commanded

What to check

Read and record freeze frame and full DTC list with a compatible scan tool
Check vehicle battery voltage and charging system (safe 12–14.5 V range)
Visually inspect fuses and fusible links for accessory circuits
Inspect accessory relay: remove and check for signs of damage, burning, oil contamination
Check connectors and wiring for corrosion, loose pins, crushed sections or rodent damage around relay and BCM
Backprobe relay coil/control terminal and supply terminal while activating the circuit with a scan tool or switch

Signal parameters

Battery supply voltage at relay supply terminal: ~11–14.5 V when system on
Relay coil/control command from BCM: near battery voltage (~11–14 V) when energized; ~0 V when off
Relay coil resistance (typical): tens to a few hundred ohms (varies by relay) — measure and compare to known-good relay
Open-circuit: infinite resistance between coil terminals or between supply and output when relay is open
High-voltage fault: measured voltage significantly above normal charging voltage (>15 V) or voltage spikes on activation

Diagnostic algorithm

Retrieve and record DTC B1451 plus any related codes and freeze-frame data with a dealer-level or professional scan tool.
Check battery voltage and charging system; correct if outside normal range before continuing.
Visually inspect fuses, fusible links and accessory relay; replace any blown fuses and test with a known-good relay if available.
With ignition off, inspect relay socket and wiring for corrosion, damage, or loose terminals; repair or clean as necessary.
Backprobe relay socket while operating accessory switch or commanding relay from scan tool: verify supply (battery) voltage, relay control voltage from BCM, and switched output. Compare to expected signal params.
Check continuity and resistance of wiring from BCM/relay driver to relay coil and from relay output to accessory load. Repair any opens/high resistance.
Verify good ground(s) for relay and BCM; measure voltage drop to chassis while circuit is energized (should be very low).
If wiring and relay check good, command and monitor the BCM output driver with oscilloscope or multimeter. If driver output abnormal, consider BCM software update or replacement after confirming wiring.
Clear codes and perform functional test / road or system test to confirm repair; re-check for reappearance of B1451.
If intermittent, perform wiggle test on harnesses and retest; inspect for heat or movement related faults.

Likely causes

Failed accessory relay
Faulty or corroded connector/wiring in relay supply or control circuit
Blown/poor fuse or fusible link
Poor ground at relay or BCM

Fault status

⚠️ Status

Accessory relay control circuit — high voltage detected or open circuit. BCM reports abnormal voltage or lack of continuity on accessory relay circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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B1451 — Accessory Relay Circuit High Voltage or Open Circuit