P0787–P078C Shift Timing Solenoid A Low
The ECU has logged a fault on P0787. The definition below is the exact wording the standard uses for this code.
Can you drive it? 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.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P0787 | Shift Timing Solenoid A Low | Investigate soon |
P078C | Shift Timing Solenoid B Low | Investigate soon |
The definition
P0787: Shift Timing Solenoid A Low.
P0787 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:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
This is the electrical side of the same shift timing solenoid: the transmission control unit is seeing a lower voltage on that valve's control circuit than it should. In practice that usually means a short to earth somewhere in the wiring, or a fault inside the solenoid's winding. The gearbox will normally protect itself by going into limp home - a fixed gear, no kickdown, often a warning on the dash. The solenoid itself lives inside the gearbox, but the wiring that reaches it does not, and that is where the cheap findings are.
Most likely causes, in order
- Gearbox connector or harness. Oil creeping up the loom, corroded or spread pins, or chafing where the harness passes the bellhousing or subframe. Unplug, inspect and refit properly; a wiggle test while someone watches live data will often reproduce it.
- Weak battery, poor earth or a charging fault. Low or unstable supply voltage sets circuit codes in several modules at once. If you have unrelated electrical faults stored elsewhere in the car, test the battery and charging before touching the gearbox.
- The solenoid winding has failed. Coils fail with age and heat. A workshop can compare that valve's resistance or current draw against its siblings in the same unit - a reading well away from the others points at the solenoid rather than the loom.
- Internal driver fault in the mechatronic or control unit. Last on the list and only once the wiring and supply are proven. Many VAG mechatronic units can be reconditioned or repaired by a specialist rather than replaced outright.
Worth knowing: Before agreeing to any internal work, prove the harness, the connector and the battery - they are the cheap end and they are where these codes usually come from. Ask specifically whether the individual valve is available for your gearbox: on VAG DSG mechatronic units the solenoids generally are not sold separately and the valve body or mechatronic is the replacement item, but on some conventional automatics an individual valve can be had, and the difference in cost is large enough to be worth the question. If a mechatronic is fitted, budget for the coding and adaptation it needs; fitted but not adapted, it will not behave.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P0787 mean?
P0787 means Shift Timing Solenoid A Low. It is logged when the ECU sees this circuit outside its expected operating window.
Can I drive with P0787?
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.