Short to voltage or damaged wiring in the stop-start status signal circuit; Corroded, loose or pushed-out pins at a connector in the signal circuit; Fault in the stop-start switch, sensor or related input device holding the signal high; Weak or poorly charged battery causing unstable voltages and false signal readings; Faulty engine control unit or related control module driver circuit; Outdated control unit software where the manufacturer lists it as a known cause.

P05FB

Stop-Start Status Signal Circuit High.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
FB: FaultThe specific fault in that area

What it means

P05FB means the engine control unit has seen the stop-start status signal circuit sitting at a higher voltage than expected. The status signal tells the system whether stop-start is active, available or inhibited, so a stuck-high reading makes the signal implausible. The exact signal path and which module sends it depend on the vehicle and engine.

Symptoms

Engine does not shut off automatically at a stop
Stop-start warning or fault message on the dashboard
Malfunction indicator lamp may be on
Stop-start indicator stays on or off regardless of conditions
Intermittent loss of stop-start function

Possible causes

Short to voltage or damaged wiring in the stop-start status signal circuitlikely
Corroded, loose or pushed-out pins at a connector in the signal circuitlikely
Fault in the stop-start switch, sensor or related input device holding the signal highpossible
Weak or poorly charged battery causing unstable voltages and false signal readingspossible
Faulty engine control unit or related control module driver circuitrare
Outdated control unit software where the manufacturer lists it as a known causerare

How to diagnose

Read all stored codes and freeze frame data to see conditions when the code set, and note any battery, network or other stop-start codes
Check battery condition and charging system voltage, as low or unstable voltage can upset stop-start signals
Visually inspect the wiring and connectors in the stop-start signal circuit for chafing, water ingress, corrosion and damage
Check the wiring diagram for your vehicle to identify the status signal circuit, its supply and its ground
With the ignition on, measure the signal circuit voltage at the control unit connector and compare it with the specification for the model
Disconnect the relevant connector and check for a short to voltage on the signal wire, then check wiring continuity end to end
Check the operation and signals of the stop-start switch or related input device against the model's data
Check whether a software update or technical bulletin exists for this code on your vehicle

How to fix

Repair or replace damaged wiring that is shorted to voltage
Clean, repair or replace corroded or damaged connectors and terminals
Replace the stop-start switch, sensor or input device if it is proven faulty
Replace or properly recharge a weak battery, then confirm charging system output
Replace or repair the control unit only after wiring and inputs have been proven good
Install a manufacturer-approved software update if an outdated calibration is a known cause

Can I keep driving?

Low severity

The car can normally be driven as usual, though stop-start will probably not work. Book it in soon, especially if the warning lamp is on or the battery seems weak.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.