P0730 Incorrect Gear Ratio

The definition

P0730: Incorrect Gear Ratio.

P0730 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. 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.
2. Check the connector at the part for corrosion, and that it is fully seated.
3. Clear the code and see whether it returns, and under what conditions.

What actually causes this on a VAG

The gearbox controller knows how fast the input shaft is turning and how fast the output is turning. Divide one by the other and you get the ratio the box is actually in - and if that doesn't match the gear it just asked for, you get this code. So this isn't a wiring fault: it's the gearbox not doing what it was told, either because something is slipping, because a valve or solenoid didn't do its job, or because one of those speed signals is lying. It usually arrives with limp home, revs flaring between shifts, or a hard bang into gear.

Most likely causes, in order

1. Old, low or cooked gearbox oil. VAG filled a lot of these boxes with what was sold as a lifetime fill; it isn't, and worn fluid loses the friction properties the clutch packs depend on. The level has to be checked with the box at the correct temperature, using the level plug and a scan tool watching the fluid temperature - checking it stone cold or fully hot gives a false answer and is a very common mistake.
2. Valve body or a shift solenoid. A sticking solenoid or a worn valve bore lets pressure bleed away, so the clutch for that gear never fully clamps and the ratio comes out wrong. If there are also gear-specific ratio codes stored, or the problem always happens on the same shift, that points firmly this way rather than at general wear.
3. A speed signal that's wrong but not obviously broken. If an input or output speed sensor drops out briefly, the ratio maths goes wrong even though the gearbox is perfectly healthy. It's less likely than genuine slip, but it costs nothing to rule out, so do it before anything comes apart: compare input and output speed side by side in live data through a road test, and check the gearbox plug for oil and corrosion while you're there.
4. Worn clutch packs. Genuine mechanical wear inside the box, and the expensive end of this list. The signs are dark, burnt-smelling fluid, heavy clutch material on the sump magnets, and slip that doesn't improve at all after a proper fluid and filter service.

Worth knowing: Get a proper fluid and filter change done with the correct specification fluid before anyone opens the gearbox - where tired fluid is the root cause it can be the whole repair, and it has to be done after any repair anyway. Just don't expect it to rescue a box that's already slipping badly and full of clutch material, and be cautious about a high-pressure 'flush' on a high-mileage car.

Common questions

What does P0730 mean?

P0730 means Incorrect Gear Ratio. It is logged when the ECU sees this circuit outside its expected operating window.

Can I drive with P0730?

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

• DSG juddering or jerking: what's normal and what isn't
• DQ200 7-Speed Dry DSG: Problems and What to Check
• DQ250 6-Speed Wet DSG: Problems, Servicing and Buying Checks
• DQ500 & DL501 S tronic: Problems, Servicing, What to Check
• Why the same fault code has completely different causes