P05B8

What it means

P05B8 is the generic definition for an open circuit fault in the restraint deployment signal circuit. The control unit that receives the crash or deployment signal from the restraint (airbag) system expects a valid signal path, and it has detected an open circuit, meaning a broken or disconnected line. What the signal controls, such as fuel shut-off or high-voltage isolation on electrified vehicles, depends on the model and engine.

Symptoms

• Engine or powertrain warning light on
• Airbag or restraint warning light on at the same time
• Stored restraint or crash-signal fault in other control units
• Possible loss of crash-related functions such as automatic fuel cut-off, depending on model
• Intermittent warning that comes and goes with wiring movement or bumps
• Usually no change in how the engine runs

Possible causes

• Damaged, chafed or broken wiring in the deployment signal circuit between the restraint control unit and the receiving control unitlikely
• Loose, corroded or pushed-out pins at a connector in the signal circuitlikely
• Previous accident, underbody or seat-area repair that left a connector unplugged or a wire damagedpossible
• Water ingress or corrosion in a connector or junctionpossible
• Fault in the restraint control unit output stagerare
• Fault in the receiving control unit input circuit, or outdated software where the manufacturer has identified it as a causerare

How to diagnose

1. Read all stored codes across every control unit, noting any restraint system codes, and record freeze frame data and when the fault set
2. Check whether the airbag warning light is on, and look up the manufacturer's circuit diagram to see which units send and receive this signal on this model
3. Visually inspect accessible wiring and connectors along the route for chafing, crush damage, water, corrosion or signs of previous repair
4. Before touching any restraint connector, follow the manufacturer's procedure to isolate the battery and wait the specified time, and only let suitably trained staff work on airbag circuits
5. Check connector pins for fit, tension and corrosion, and wiggle-test the harness while watching live data for the fault changing
6. With the circuit isolated and per the manufacturer's procedure, test the signal wire for continuity and for shorts to ground or supply, without probing airbag squib circuits
7. Clear the code and road test, then re-read to confirm whether the fault returns

How to fix

• Repair or replace the damaged section of wiring using the correct specification of wire and sealed joints
• Clean, re-seat or replace corroded or loose connectors and terminals
• Correct any connector left unplugged or mis-fitted after previous repairs
• Dry out and seal any area with water ingress, then repair the affected terminals
• Replace the faulty control unit only after wiring and connectors are proven good, and have it coded as the manufacturer requires

Can I keep driving?

Nearby codes

• P05B7GenericActive Grille Air Shutter B Supply Voltage Circuit High
• P05B9GenericRestraint Deployment Signal Circuit Low