P0659–P2686 Actuator Supply Voltage A Circuit High

Which code is which

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

The definition

P0659: Actuator Supply Voltage A Circuit High.

P0659 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.

What to check first

Cheapest and fastest checks first:

1. Unplug the sensor and check whether the signal falls. If it stays high, suspect the wiring rather than the sensor.
2. Check the earth path - a missing earth makes a sensor read high.

What actually causes this on a VAG

This is the same actuator supply rail as P0657, but the opposite complaint: the ECU sees voltage on it that is higher than expected, or present when the rail should have been switched off. The car may drive normally, or it may light a warning and go into a reduced power mode. The most likely cause is a short to a live feed somewhere in the wiring - but there is one whole-car check worth doing first because it costs nothing.

Most likely causes, in order

1. Whole-car charging voltage out of spec (check this first, it's free). Before anything is unplugged, have the charging system output measured and compared against the specification for your car. If system voltage is running high, over-voltage complaints can turn up in several unrelated places at once, and an overcharging alternator or regulator quietly damages the battery and control units while you chase looms. Modern VAG cars deliberately vary charging voltage under energy management, so it needs comparing against spec rather than against a number off the internet. If it checks out, you've ruled it out and lost nothing.
2. Short to positive in the loom. This is the usual answer for a 'circuit high' fault. A chafed wire touching a permanently live feed back-feeds the rail and holds it up when the ECU has switched it off. Look where the harness crosses metal edges, passes near the exhaust, or has recently been disturbed by other work - and check inside connectors for damp or corrosion bridging between a live pin and the rail.
3. Relay contacts stuck closed. If the supply relay's contacts have welded, the rail stays live regardless of what the ECU commands. Less common than a wiring short, but it costs nothing to test: swap it with an identical relay from the same carrier and see whether the behaviour follows the relay.
4. ECU internal fault. The ECU's own monitoring or switching of that rail can fail, but treat this as the last explanation rather than the first, and only after the charging system and the wiring have been checked and cleared.

Worth knowing: Have the charging system output checked before anyone starts probing looms - it's a minute's work and it rules out a fault that affects the whole car. And when this code appears next to a batch of other unrelated over-voltage faults, look for the one thing they all share rather than treating each code as its own separate repair.

Common questions

What does P0659 mean?

P0659 means Actuator Supply Voltage A Circuit High. The voltage on this circuit is sitting near battery voltage. Typically a short to a positive feed, or a disconnected sensor floating high.

Can I drive with P0659?

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

• Battery Keeps Going Flat on a VW or Audi: Finding the Cause
• VW or Audi will not start: working out which problem you have
• Several warning lights on at once: usually one cause, not many
• Why the same fault code has completely different causes