P0999 Gearbox solenoid: signal or voltage too high ("F")
P0999 means: Gearbox solenoid: signal or voltage too high ("F"). The automatic gearbox module has found a fault. Drive gently and have the car checked soon. The most common repair costs about €45–90 in Estonia, depending on make and model. The most common cause: connector loose, damp or corroded.
What it means
The automatic gearbox module has found a fault. The gearbox may go into limp mode: it holds one gear and shifts harshly or not at all. The signal voltage is too high. Usually a wire is shorted to power, the ground is broken or the part itself has failed.
Multi-page report for your car: €2.99
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Approximate estimate, not a final diagnosis. We can only say for sure once we've checked the car.
The free answer explains the code. The report tells you what to do with YOUR car.
General explanation of the code and the main causes.
- Causes and symptoms for your make, model and engine
- Step-by-step check path: what you can try yourself, cheapest first
- Fuse box diagrams, if we have data for your model
- Likely repairs and their prices
- Is it safe to drive and how soon to act
- PDF by email, yours to keep
- What the code means
- Likely causes on your car
- Step-by-step troubleshooting
- Repairs and prices
- Can I drive, and what not to postpone
- What to ask at the workshop
- If you come to us
If you come to our workshop in Haapsalu within 60 days, we deduct €2.99 from diagnostics or repair. Same car only; quote the report code.
What you may notice
- Stuck in one gear (limp mode)
- Harsh or late gear changes
- Gearbox slipping
- Engine or gearbox light on
What could be wrong
- 1Connector loose, damp or corroded · Wiring or connector repair €45–90
- 2Wire shorted to power or ground broken · Wiring or connector repair €45–90
- 3Faulty solenoid or sensor · Gearbox solenoid replacement €250–500
- 4Engine computer fault (rare) · Control unit check and software €150–300
Repair difficulty: Hard
What you can check yourself
First look at the connector and wiring: anything loose, melted or green with corrosion? Read the gearbox module's own codes too. If the gearbox slips, drive gently and don't tow a trailer. Best left to a workshop. It needs a diagnostic tool and experience.
How we fix it
- We read the fault data on the diagnostic tool and check whether the fault is constant
- We measure the circuit's supply, ground and signal
- We repair the wire or replace the connector
- If the wiring is fine, we replace the solenoid or sensor
Standard SAE description: Shift Solenoid "F" Control Circuit High