Broken or chafed wire in the idle speed control valve solenoid circuit, often near the connector or where the harness bends; Corroded or loose electrical connector at the idle speed control valve; Failed opening solenoid inside the idle speed control valve assembly; Open circuit inside the valve due to internal winding failure from heat and age; Damaged or oxidized pins in the DME connector affecting the solenoid control circuit; Rodent damage to the wiring harness in the engine bay

DTC codes / BMW codes / P1508

P1508 · BMWIdle Speed Control Valve Opening Solenoid Control Open Circuit

P1508 on BMW vehicles indicates that the engine control module (DME) has detected an open circuit in the electrical path to the idle speed control valve's opening solenoid. The computer commands a specific idle speed, but the solenoid circuit shows no continuity, so the valve cannot adjust airflow as intended.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Unstable or fluctuating idle speed, sometimes surging or dipping below normal
Engine may stall when coming to a stop or when the throttle is released
Rough idle quality, especially when the engine is cold or under electrical load
Inconsistent idle speed after the engine warms up, despite the DME attempting to compensate

Common causes, most likely first

Broken or chafed wire in the idle speed control valve solenoid circuit, often near the connector or where the harness bends
Corroded or loose electrical connector at the idle speed control valve
Failed opening solenoid inside the idle speed control valve assembly
Open circuit inside the valve due to internal winding failure from heat and age
Damaged or oxidized pins in the DME connector affecting the solenoid control circuit
Rodent damage to the wiring harness in the engine bay

How to diagnose and fix it

Perform a visual inspection of the idle speed control valve connector and the wiring harness for damage, corrosion, or loose pins
Disconnect the valve connector and measure resistance across the opening solenoid terminals; compare to BMW specifications for the engine
Check for continuity from the valve connector to the DME connector on both solenoid control wires to isolate an open circuit
Inspect the DME connector pins for corrosion or push-back, and repair any damaged terminals
If the circuit tests good, substitute a known-good idle speed control valve and clear the code to see if it returns
Repair or replace the faulty section of wiring harness, using proper crimp and seal techniques
After repair, clear the DME adaptations and perform an idle relearn procedure if applicable to the model

When the valve is not the culprit

A chafed wire behind the intake manifold or near the throttle body is a frequent cause that gets missed when technicians replace the valve without testing the circuit first.
The DME may set P1508 intermittently if the connector is only loose when the engine moves under torque, so wiggle-testing the harness while watching live data is essential.
On some BMW engines, the idle speed control valve shares a ground circuit with other sensors, and a bad ground can mimic an open solenoid circuit.
A failed valve can sometimes still show correct resistance when cold but open internally when hot, so testing should include a heat soak if the fault is intermittent.
This code does not always mean the valve is dead; a simple unplugged connector after recent service is a common and easily overlooked cause.

Can I keep driving with P1508?

You can usually drive the car to a repair shop, but expect a rough or stalling idle that may worsen in traffic or when the engine is cold. Avoid prolonged idling and be prepared for the engine to stall when you lift off the throttle, especially at low speeds.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.