P0047
PowertrainTurbocharger/Supercharger Boost Control A Circuit Low
Most of the time this is a tired boost control solenoid or its wiring, sitting right next to a turbo that cooks everything around it with heat and vibration. The ECU drives that solenoid with a voltage signal, and when it reads the voltage on that circuit as too low, it logs P0047. The car will usually drop into limp mode to protect the turbo until it's sorted.
ⓘ Information only. This page provides general educational information about fault code P0047. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0047 mean?
P0047 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Turbocharger/Supercharger Boost Control A Circuit Low.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes with the car already holding back power
- • Flat, gutless acceleration, especially pulling up a motorway slip road or climbing a hill
- • Limp mode kicking in, where the car refuses to rev past a certain point and feels strangled
- • Boost that just isn't there, the throttle feels disconnected from what the engine does
- • Fuel economy creeping up because the engine is running outside its happy range
- • On some cars a faint hiss or whistle from the engine bay if there's a split hose alongside the fault
Possible causes
Causes commonly associated with P0047, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Boost control solenoid valve gone faulty, usually from the coil resistance drifting or the valve sticking after years of heat cycles. This is where to look first
- 2. Corroded or damaged wiring and connectors near the turbo, where heat and road muck make short work of plugs and looms over time
- 3. Poor earth on the ECU or boost circuit, throwing the voltage reading off enough to trip the code
- 4. Boost pressure sensor or vane position sensor feeding the ECU duff figures
- 5. A short or break in the harness between the ECU and the solenoid, often intermittent and a pain to chase
- 6. Split or perished vacuum hose to the boost actuator on vacuum-controlled setups
- 7. ECU output driver failed, which does happen but it's well down the list and you only land here after everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the codes and live data, clear them, then drive the car and see if P0047 comes straight back. A code that returns within a mile or two is a live fault, not a one-off glitch
- 2. Get under the bonnet and physically check the solenoid connector and the loom running to it. Wiggle the plug, look for green corrosion, melted insulation, and pins backed out of the connector
- 3. Clean and check the battery terminals and the main engine earth straps before you spend money on parts. A bad earth fakes a low-voltage fault beautifully
- 4. Back-probe the solenoid connector with a multimeter, ignition on. You're looking for a supply around 4.5 to 5.0V on the signal side. Sat below 3.0V tells you the circuit really is low, not just the ECU complaining
- 5. Measure the solenoid resistance with an ohmmeter and compare to the manual figure for your engine. While you're there, command it on and off with a bi-directional scan tool and listen for a clean click
- 6. If the wiring, earths and solenoid all pass, only then start eyeing the boost sensor and, last of all, the ECU driver
Common questions about P0047
How do I know if it's the solenoid itself or just the wiring to it? +
Cheapest way to tell them apart is a multimeter at the solenoid plug. Test the resistance of the solenoid coil and compare it to the figure in the manual for your engine. If the coil reads way out of spec or open, the solenoid is the fault. If the coil reads fine but you've still got low voltage at the plug, the problem is upstream in the wiring, the connector, or an earth. Loads of P0047s on higher-mileage diesels turn out to be a corroded connector cooked by turbo heat rather than a dead solenoid, so don't just throw a new valve at it without checking the plug first.
How long does this usually take to put right? +
A solenoid swap on a car where the part is easy to reach is often under an hour of labour plus the diagnostic time. The trouble is access. On some engines the boost solenoid is buried behind pipework and you're pulling bits off to get to it, which pushes it to a couple of hours. Chasing an intermittent wiring fault is the real time-sink, you can lose a morning tracing a loom for a break that only shows up when the engine's hot and vibrating.
Is a cheap aftermarket solenoid any good or should I stick with the genuine part? +
A decent branded aftermarket solenoid from a known name like Pierburg or Bosch is fine and usually a fair bit cheaper than main dealer pricing. They make a lot of these for the manufacturers anyway. What I'd steer clear of is the bargain-basement unbranded stuff off the auction sites, because boost solenoids see real heat and a poorly made one can fail again inside a year and dump you back into limp mode. Buy a reputable brand, fit it once.
Can I keep driving with this for a bit? +
A short run to the garage is generally alright, but I wouldn't make a habit of it. The car will likely be in limp mode anyway so you've lost most of your power. Driving for weeks with the boost control out can let exhaust temperatures and soot build up, and on a turbo diesel that's not kind to the turbo or the DPF over time. Get it looked at sooner rather than living with it.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →