P2AB4: Cold Start Intake Manifold Runner Control Stuck Open Bank 2
What to do
Expect rough running from cold that clears once warm, or a loss of top-end power — depending on which way it is stuck. Carbon build-up in the intake is the usual cause, and cleaning is often possible rather than replacement.
What this code means
The cold start intake manifold runner control on bank 2 is stuck open.
Intake manifold runner control changes the shape of the air path, and doing it at cold start is a specific emissions measure rather than a performance one.
A long, narrow intake runner makes air arrive fast and swirling; a short, wide one lets more air in at high revs. Variable runners give an engine both, and normally the control is about torque across the rev range.
At cold start the goal is different: mixing. Cold fuel does not vaporise well and cold cylinder walls condense it, so a cold engine burns a poorer mixture than a warm one. Forcing the incoming air into a tight swirl mixes fuel and air far better, which cuts unburnt hydrocarbons during exactly the window when the catalyst cannot deal with them.
So a runner stuck in the wrong position produces a fault with a temperature and a bank attached. Stuck open, the swirl never happens: rough cold running, and hydrocarbons the catalyst cannot yet treat. Stuck closed, the restriction persists once warm, which shows as a top-end power loss the driver notices on one bank only — an oddly lopsided-feeling engine.
Carbon is the usual cause, as it is for anything with a flap in the intake of a direct-injection or diesel engine, and it accumulates over years rather than failing suddenly.
Stuck open means no swirl when it is wanted. The engine runs rough from cold and clears as it warms, and the emissions cost lands in the window where it matters most.
Likely causes
Start here
- Carbon deposits on intake manifold flaps · moderate
- Failed manifold runner actuator · specialist
Less common
- Corroded or loose connector · specialist
- Control module driver failure · specialist
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
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