P0079
PowertrainExhaust Valve Control Solenoid Circuit Low (Bank 1)
The exhaust valve control solenoid on bank 1 is what lets the ECU adjust your exhaust valve timing on the fly, mostly to balance power, economy and emissions. P0079 means the ECU has seen the voltage in that solenoid's control circuit drop too low, which usually points to a wiring fault, a dead solenoid, or a short to earth somewhere in between. With the timing control out of action the engine can't optimise valve events, so you get the warning light and often a flat, lazy feel under load. It's an electrical complaint at heart, not a worn-out engine, so the fix is normally about tracing the circuit rather than rebuilding anything.
ⓘ Information only. This page provides general educational information about fault code P0079. 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 P0079 mean?
P0079 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Exhaust Valve Control Solenoid Circuit Low (Bank 1).
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:
- • Check engine light on, sometimes with the car dropping into limp mode
- • Noticeably flat acceleration, especially when you put your foot down at motorway speeds
- • Lumpy or shaky idle that you can feel through the seat
- • The odd stall as you lift off the throttle coming up to a junction
- • Fuel economy creeping the wrong way over a few tankfuls
- • A general sluggish, hesitant feel when pulling away
Possible causes
Causes commonly associated with P0079, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Damaged or corroded wiring in the harness running from the ECU to the solenoid, the most common cause and worth checking before you condemn anything else
- 2. A loose or corroded connector at the solenoid itself, often green or crusty after a few British winters
- 3. The exhaust valve control solenoid failing internally with a shorted or open coil
- 4. A short to earth in the control circuit, which is exactly the kind of fault that pulls the voltage low and triggers this code
- 5. Oil getting into the solenoid and fouling the windings, more likely on a higher-mileage engine with sludge
- 6. A failed ECU output driver for that circuit, rare but it happens once everything else checks out clean
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. Plug in a scan tool and read every stored code plus the freeze frame, because what else is logged usually tells you whether this is a one-off or part of a wider timing problem
- 2. Get your hands on the connector at the solenoid and inspect the pins and harness for corrosion, chafing or a pin that's backed out of the housing
- 3. Measure the solenoid coil resistance with a multimeter and compare it against the manufacturer's spec, an open or shorted reading condemns the solenoid on the spot
- 4. With the ignition on, check you've got a clean voltage supply and a solid earth at the connector before you blame the part
- 5. Back-probe the ECU control signal while a helper operates the system, so you can see whether the module is actually commanding the solenoid
- 6. Clear the code and take it for a proper drive to see if it comes back under real load rather than just idling on the drive
Common questions about P0079
How long should this take to sort out at a garage? +
Diagnosis is usually an hour or so on the ramp while they read the codes and probe the circuit. If it turns out to be a corroded connector or a chafed wire, the repair itself can be quick, maybe another hour. Replacing the solenoid depends entirely on where it sits on your particular engine, some are easy to reach and others are buried under the intake, so allow anything from one to three hours of labour. The wiring fault is what eats the time, because finding a break in a loom is fiddly work.
Is a cheap aftermarket solenoid worth it or should I stick with OEM? +
For a timing control solenoid I'd lean towards OEM or a recognised brand like Bosch or Hella rather than the cheapest one on a marketplace listing. These parts work to fine tolerances and a no-name unit with slightly off coil resistance can either fail early or set the code straight back. A quality solenoid is usually low-to-mid three figures, and given the labour to get at it, you don't want to be doing the job twice for the sake of saving twenty quid.
Can I keep driving with this showing? +
You can drive short distances, but I wouldn't make a habit of it. With the exhaust valve timing stuck where it is, the engine isn't running as it should, and if the car has dropped into limp mode you'll be crawling along well below normal power anyway. The bigger worry is that an underlying short or wiring fault doesn't tend to fix itself and can drag other circuits into the problem. Get it looked at sooner rather than nursing it for weeks.
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 →