Leaking, split or disconnected vacuum hose between the engine and brake booster; Faulty or leaking one-way check valve at the booster; Faulty BBV sensor or damaged sensor seal; Wiring or connector fault in the sensor circuit (open circuit, short, corrosion, poor reference or ground); Leaking brake booster diaphragm; Low engine vacuum from an engine fault, such as a large intake leak or mechanical problem; Fault in the powertrain control module.

P1578

BBV Sensor Circuit Low Vacuum.

Chrysler
Powertrain
Manufacturer code
High severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
5: AreaVehicle speed, idle control and auxiliary inputs
78: FaultThe specific fault in that area

What it means

P1578 on a Chrysler means the powertrain control module has seen a signal from the brake booster vacuum (BBV) sensor that indicates low vacuum in the brake booster. Either the booster is not getting enough vacuum, or the sensor or its circuit is giving a reading that looks like it. Because the booster supports braking, treat the code as a possible brake safety issue until proven otherwise.

Symptoms

Brake pedal feels hard or needs more effort, especially after several applications
Hissing noise from the pedal area or engine bay when braking
Rough idle or high idle if a vacuum leak is present
Brake warning light or engine warning light on
Longer stopping distances than normal

Possible causes

Leaking, split or disconnected vacuum hose between the engine and brake boosterlikely
Faulty or leaking one-way check valve at the boosterlikely
Faulty BBV sensor or damaged sensor sealpossible
Wiring or connector fault in the sensor circuit (open circuit, short, corrosion, poor reference or ground)possible
Leaking brake booster diaphragmpossible
Low engine vacuum from an engine fault, such as a large intake leak or mechanical problemrare
Fault in the powertrain control modulerare

How to diagnose

Read the stored and pending codes and the freeze frame data, noting engine speed, load and conditions when the code set, and check for other vacuum or engine codes
Check the brake fluid level and perform a brake pedal feel test: with the engine off, pump the pedal until hard, hold it down, start the engine and see whether the pedal sinks slightly
Visually inspect the vacuum hose, check valve and connections between the engine and booster for cracks, splits, collapse or loose fittings
Listen for hissing with the engine running and the brake pedal pressed or released, which can point to a leak at the booster or hose
Inspect the BBV sensor, its connector and wiring for damage, corrosion, water ingress or chafing
View the live BBV sensor value with the engine off and at idle, and compare it with the expected values for that model, as the specification varies by model and engine
Test the sensor supply, reference and signal wiring for continuity, shorts and voltage against the wiring diagram for that vehicle
Check the check valve for one-way operation and measure the engine's manifold vacuum to rule out a general engine fault

How to fix

Replace any damaged, split or loose vacuum hose and make sure the connections are secure
Replace the faulty brake booster check valve
Replace the BBV sensor if it reads incorrectly and its wiring has tested sound
Repair damaged wiring or connectors in the sensor circuit
Replace the brake booster if the diaphragm is leaking
Correct any underlying engine vacuum problem, then clear the code and confirm it does not return after a road test

Can I keep driving?

High severity

Avoid driving until the brake booster and vacuum supply have been checked, as lost brake assist can greatly increase pedal effort and stopping distance. If the brakes feel normal and the car must be moved, drive only a short distance with great care and leave extra stopping room.

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