P2100–P210A Throttle Actuator A Control Motor Circuit/Open

Which code is which

Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.

The definition

P2100: Throttle Actuator A Control Motor Circuit/Open.

P2100 is a manufacturer-specific powertrain code (the engine or gearbox). Its meaning is set by the carmaker rather than by the SAE standard, so a generic OBD-II reader will often show it as an unknown code or misread it.

What to check first

Cheapest and fastest checks first:

1. Check the connector is fully seated and the locking tab is engaged. A half-seated plug is the single most common cause of an open circuit.
2. Back-probe the pins and check continuity from the part back to the module connector.
3. Inspect for a pushed-back or corroded terminal - the wire looks fine but the pin has backed out of the housing.

What actually causes this on a VAG

Virtually every petrol VAG built since the early 2000s uses a drive-by-wire throttle: there is no cable from your pedal, and a small electric motor inside the throttle valve control module - VAG's own designations are J338 for the module and G186 for the motor - opens the flap when the engine ECU tells it to. P2100 means the ECU cannot see a working circuit to that motor at all, as if the wire were cut. The flap then falls back to its sprung limp-home position, barely open, so you typically get the EPC light, very little power and a car that will crawl but not pull away properly. On a TDI the same actuator is the electric intake/EGR throttle flap rather than a load-control throttle, so the picture is different there - rough shutdown, EGR complaints or reduced power rather than a dead pedal.

Most likely causes, in order

1. Damaged wiring or a dirty connector at the throttle body. Free to check, so start here. The throttle body plug lives in engine heat and vibration, and the loom to it often chafes where it crosses a bracket or heat shield. With the ignition off, unclip the plug and look for green or white corrosion, a lead that has rubbed through, and - easily missed - a pin pushed back into the housing so it no longer makes contact. A backed-out pin looks identical to a broken wire on the scan tool and costs nothing to fix. A wiggle test with the engine idling and live data on screen will usually make an intermittent one show itself.
2. Missing power feed, a poor earth, or a tired battery. Still cheap, and worth doing before anything is bought. A blown fuse, a failing relay or a corroded engine earth point can starve the throttle unit and log an open circuit. A weak or dying battery does the same and normally drops several unrelated electrical codes at once, so check charging and battery health - and scan the other modules for a scatter of low-voltage faults - before condemning any single component.
3. The throttle body's motor has failed internally. This is a genuinely common failure on VAG once the wiring has been cleared, not a long shot. The motor's brushes and windings wear with age and eventually go open circuit. On VAG the unit is replaced complete, not repaired. A workshop can confirm it by measuring across the motor pins at the throttle body itself with the plug off, rather than guessing from the code.
4. Engine ECU output stage. The driver circuit inside the ECU can fail, but it is genuinely rare and should be the last thing considered. Only conclude this once the loom, connector, supplies and the throttle unit itself have all been proved good, as an ECU also needs coding and immobiliser matching.

Worth knowing: After anything is done to a throttle body - cleaning, unplugging, replacing, or on some cars simply a flat battery - the throttle has to be re-adapted with diagnostic software before it behaves. On most VAG engine ECUs that is a Basic Settings routine (group 060 on many of them), and VAG even has a dedicated fault for skipping it. A brand new throttle body that still idles badly or feels dead is very often just an un-adapted one. Two cautions: switch the ignition off before unplugging the throttle body, or you will simply add a pile of throttle-position codes to the pile you already have; and do not blast the inside with aggressive carburettor cleaner, as it can ruin the coating and the built-in position sensors.

Common questions

What does P2100 mean?

P2100 means Throttle Actuator A Control Motor Circuit/Open. The circuit is broken somewhere - a cut wire, a corroded pin or an unplugged connector means the signal never arrives.

Can I drive with P2100?

The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.

Related reading

• Throttle body adaptation on a VW or Audi: why cleaning alone
• Rough Idle on a VW or Audi: Causes and How to Narrow It
• VW or Audi feels flat and has lost power: where to look
• Why the same fault code has completely different causes