Faulty idle speed control valve with an open closing winding; Corroded, loose or damaged connector at the idle control valve; Open circuit or high resistance in the wiring between the valve and the engine control unit; Chafed or broken wiring loom, often from heat or vibration near the engine; Poor power supply or earth affecting the valve circuit, such as a fuse or relay fault (depends on model); Fault in the engine control unit output driver.

P1504

Idle Speed Control Valve Closing Solenoid Control Open Circuit.

BMW
Powertrain
Manufacturer code
Medium severity

How this code is built

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

What it means

On BMW, P1504 means the engine control unit has detected an open circuit in the control of the idle speed control valve's closing solenoid. The valve regulates the air bypassing the throttle at idle, and the control unit saw no current flow or an out-of-range voltage on the closing side of the circuit. The exact valve design, and whether it has one or two windings, depends on the model and engine.

Symptoms

Unstable, hunting or surging idle
Engine stalls at idle or when slowing to a stop
Idle speed too high or too low
Difficult starting, especially when cold
Engine management warning light on
Poor idle quality when electrical loads such as the air conditioning come on

Possible causes

Faulty idle speed control valve with an open closing windinglikely
Corroded, loose or damaged connector at the idle control valvelikely
Open circuit or high resistance in the wiring between the valve and the engine control unitlikely
Chafed or broken wiring loom, often from heat or vibration near the enginepossible
Poor power supply or earth affecting the valve circuit, such as a fuse or relay fault (depends on model)possible
Fault in the engine control unit output driverrare

How to diagnose

Read all stored codes and freeze frame data, then note whether the fault is constant or intermittent and whether any other idle or air supply codes are present.
Visually inspect the idle control valve, its connector and the nearby wiring for damage, heat damage, oil contamination, corrosion or bent pins.
Check the relevant fuses and relays and confirm battery voltage and earth quality using the wiring diagram for the specific model and engine.
With the connector disconnected, measure the resistance of the valve windings and compare it with the manufacturer's specification for that engine.
Back-probe or test the valve control signals at the connector with the ignition on, and check for the expected supply and switched signal from the control unit.
Perform a continuity and short-to-earth or short-to-supply test of each wire between the valve connector and the control unit, with the control unit disconnected.
Wiggle the loom and connector while monitoring idle behaviour or live data to find intermittent faults.
Only after the wiring and valve are proven good, consider testing the control unit output.

How to fix

Replace the idle speed control valve if the winding is open or out of specification, then carry out any required idle adaptation or reset.
Clean, repair or replace the corroded or damaged connector terminals.
Repair or replace the open-circuit or damaged section of wiring, using proper soldered and sealed joints.
Restore the correct power supply or earth by replacing the faulty fuse, relay or poor earth connection.
Repair or replace the engine control unit only if it is confirmed faulty after all other tests, and have it coded or programmed as required.

Can I keep driving?

Medium severity

The car can usually be driven short distances, but stalling at junctions or at low speed can be a safety risk. Have it fixed soon, and avoid driving it if it stalls repeatedly.

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