Drive-by-wire throttle motor circuit open.
P2100 — also written P21OO, P 2100, 2100 — is the OBD-II code for electronic throttle motor circuit open. Same code, same fix: this page covers every spelling of it.
This code means the engine's brain (ECU) has lost its handshake with the motor that opens the butterfly valve. It’s a common headache on VAG 2.0 TDi engines and older Vauxhalls where the wiring loom gets brittle.
P2100 is a fuel & air fault code, typically costing £200–£700 to put right in a UK garage.
What P2100 actually feels like to drive
- The car is in 'Limp Mode'—you’re foot-to-the-floor and lucky to hit 30mph.
- The 'Engine Management Light' and 'Electronic Stability Programme' (ESP) lights are both glowing on the dash.
- A complete lack of response when you press the accelerator pedal; it’s literally dead.
- The engine starts but sits at a rock-steady, high idle (usually around 1,200 to 1,500 RPM).
- Erratic surging or 'hunting' idle if the circuit is making intermittent contact.
What causes P2100?
- Failed throttle body
- Wiring open
UK vehicles that throw P2100 most often
- VW Golf/Passat 2.0 TDi (BKD/CBAB) 2005-2015
- Vauxhall Insignia 2.0 CDTi (A20DTH) 2008-2017
- Ford Focus 1.6 Ti-VCT 2011-2018
- Audi A3/A4 2.0 TDi 2004-2013
- Skoda Octavia 1.9/2.0 TDi 2006-2013
How P2100 is fixed
- Replace throttle body and re-adapt
- Repair wiring
The P2100 misdiagnosis that wastes money
I’ve seen dozens of lads rush to fit a second-hand throttle body from a breakers yard, only to find the P2100 stays put. The real 'gotcha' on these, especially on the VW Group cars like the Golf or Leon, isn't the motor itself but the wiring loom where it rubs through near the starter motor or under the airbox. People also get blinded by the 'Open Circuit' text and ignore the pins in the connector—I've lost count of how many times I've found green crusty corrosion inside the plug that just needed a proper clean with DeoxIT, not a £300 part.
What a UK garage should charge for P2100
A diagnostic scan at an indie will run you £50 to £90. If it’s just a broken wire, you’re looking at £120 for a loom repair. If the unit’s shot, a quality Bosch or Pierburg throttle body costs between £180 and £350 plus an hour’s labour (£60-£100). If you go to a main dealer, expect a bill closer to £700 once they’ve added their 'genuine part' markup and £150-an-hour labour rate. Stick to a decent independent garage for this one.
P2100 repair cost in the UK
Most P2100 repairs land between £200–£700 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P2100
Before you let a garage sell you a new throttle unit, ask them to do a 'load test' on the wiring, not just a continuity beep. A single strand of copper can give a 12V reading on a multimeter but won't have the guts to move the motor flap. If it’s a Vauxhall, insist they check the ECU pins for 'wicking'—that's when oil or coolant travels up the loom and fries the board. Also, if they replace the unit, make sure they perform the 'Throttle Position Adaptation' using VCDS or Snap-On tools, or the car will hunt for an idle like a dog chasing its tail.
Can you drive with P2100?
Limp mode likely.
Urgency: high.