P2012: Intake Manifold Runner Control Circuit Low (Bank 2)

On a single-bank engine a circuit low fault has one shape: a conductor has found a path to ground. On a two-bank engine there is a second shape, and it is the one people miss.

The two runner control wires leave the module side by side. They are usually adjacent pins in the same connector, they usually travel together in the same loom for most of their length, and on many vehicles they pass through a shared bulkhead grommet or a common splice pack before dividing. Insulation that breaks down between two neighbouring wires connects them to each other, not to the body. And when one output is commanded on while the other is off, a wire-to-wire short between them looks exactly like a short to ground from the point of view of whichever driver is currently switched off — its line is being dragged down by its neighbour.

That gives this code a test that a single-bank circuit low code has no use for. Disconnect both actuators and both ends at the module, then measure continuity between the Bank 1 and Bank 2 control wires. Any reading at all is the answer, and it explains what would otherwise be a confusing symptom set: codes that alternate between banks, or a fault that only appears when the runners are commanded to move rather than at key-on.

The same logic applies to code pairings. If P2009 and P2012 are both stored — circuit low on both banks — a coincidence of two independent shorts is implausible. What is likely is either one wire-to-wire short between the two circuits, or a common point that has failed: a shared connector flooded with water, a splice corroded inside the loom, or a module driver stage that has taken both outputs down together. Look at what the two circuits share before looking at either one alone.

One of the two branches also has a moisture story, and which one depends on the engine. On a transversely mounted V the banks sit front and rear, and the rear bank's harness runs along the back of the engine below the cowl and windscreen scuttle, where every leaf, every blocked cowl drain and every failed windscreen seal sends water down onto it. Whether that is bank 2 has to be read off the cylinder numbering rather than assumed: on the transverse V6 families that dominate front-wheel-drive vehicles - Honda J35, Toyota 2GR-FE, Nissan VQ35 - cylinder 1 sits on the rear bank, which makes bank 2 the front bank facing the radiator and puts the cowl-water story on bank 1 instead. Other designs number the other way round. Either way, water sitting in a connector is a slow, reversible short to ground: the code appears in wet weather, disappears in dry weather, and no amount of continuity testing on a sunny afternoon will reproduce it. If the fault correlates with rain or with washing the car, work out which bank is the cowl-side one, clear its drains and open the connectors before opening the loom.

As elsewhere in this block, expect the module to protect its driver by shutting the output down, which drops the flaps to whatever position their return spring holds and usually stores a stuck-runner code for that bank alongside. That companion code is the module reporting its own reaction, not a second failure. The de-energised rest position is a design choice and the library will not assert it either way: Ford's IMRC housings use a return spring that holds the plates CLOSED, so a disabled actuator there parks them shut and gives up top-end breathing, while other designs spring open and give up low-speed torque instead. Read which arrangement this engine uses off the wiring or vacuum diagram before predicting a symptom or a companion code from it. So whether the code beside this one reads stuck-open or stuck-closed is a fact about the engine rather than about the fault.