P2390: Diesel Intake Air Flow B Control Circuit/Open

P2390 concerns the drive circuit of the second electronically operated intake throttle that some diesel engines carry; which flap a maker labels A or B is its own choice. With the driver switched off, the engine module checks whether the motor circuit is closed; an open wire, a pulled connector or a burnt motor winding sets this code. No manufacturer publishes P2390 with thresholds. For the A valve (P02E0) GM's 2017 diesel tables look for a load resistance above 200 kΩ in 160 of 200 checks at 12.5 ms, provided the relay feeds more than 11 V, as a two-trip fault. A dead motor leaves the return spring to hold the flap open on most designs, so the vehicle drives normally while EGR control and regeneration heating lose authority.

Symptoms

• MIL on, often without a noticeable change in driving
• Particulate filter regeneration delayed or blocked
• Engine may shake more when switched off because the flap no longer closes

Most likely causes

• Connector at the B throttle unplugged, loose or with pushed-back terminals
• Broken motor lead in the harness between module and throttle
• Open motor winding inside the throttle unit
• Faulty output stage in the engine control module

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the vacuum hoses and the connector
2. Check the continuity of the wire between the component and the control module.
3. Watch the actuator's movement with the scanner
4. Inspect the manifold for carbon buildup
5. Replace the actuator if it does not follow the command

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P2390 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 3: Ignition and misfires
• 90: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2390?

You can drive in moderation. Get it repaired soon, because a loose flap can cause major damage on some engines.

What causes code P2390?

The most common causes are: connector at the B throttle unplugged, loose or with pushed-back terminals; broken motor lead in the harness between module and throttle; open motor winding inside the throttle unit.

Related codes

• P2392Diesel Intake Air Flow B Control Circuit Low
• P2393Diesel Intake Air Flow B Control Circuit High
• P239BDiesel Intake Air Flow B Control Motor Current Range/Performance
• P2391Diesel Intake Air Flow B Control Performance
• P02E0Diesel Intake Air Flow A Control Circuit/Open

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 17OBDG04 Engine Diagnostics
• ms-motorservice.com: throttle valves and regulating throttles

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.