P0733
PowertrainGear 3 Incorrect Ratio
Your gearbox works out which gear it's in by comparing input shaft speed against output shaft speed. When you select third, the ratio between those two should land on a fixed number the TCM expects. P0733 means the maths didn't add up in third: the box is turning at the wrong speed for the gear it thinks it's in, which usually points to clutches slipping inside the transmission. For the driver, that's third gear feeling like it's revving without pulling, and an automatic that's starting to show its age.
ⓘ Information only. This page provides general educational information about fault code P0733. 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 P0733 mean?
P0733 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Gear 3 Incorrect Ratio.
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:
- • Engine warning light on, sometimes with a flashing gear indicator or 'D' light
- • Third gear slips, the revs climb but the car doesn't pull the way it should
- • Shifts into or out of third feel delayed, then arrive with a thump
- • Sluggish acceleration in the speed band where third would normally do the work, roughly 25 to 45 mph
- • Car drops into limp mode and refuses to shift past third, sometimes locking in a single gear
- • Whining or shuddering through the gearbox under load when the fault is mechanical
Possible causes
Causes commonly associated with P0733, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Worn clutches or bands inside the gearbox, the most common reason on a higher-mileage automatic. The friction material lets go under load and third can't hold the ratio
- 2. Low or burnt transmission fluid, which kills the hydraulic pressure the clutches need to clamp. Sniff the dipstick, burnt fluid smells like scorched toast
- 3. A sticking or failed shift solenoid that won't apply third gear cleanly
- 4. Input or output speed sensor giving a dud reading, so the TCM calculates a ratio that was never really wrong
- 5. Valve body fault or a blocked fluid passage starving the third gear circuit of pressure
- 6. Corroded wiring or a poor connector at the gearbox plug feeding the speed sensors false data
- 7. TCM software glitch or, less often, a hardware fault in the control module itself
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. Check the fluid level and condition with the engine warm and running, on the proper procedure for that box. Low or dark, burnt-smelling fluid explains a lot of P0733s before you touch anything else
- 2. Pull all stored codes. If you've got input or output speed sensor faults sitting alongside it, fix those first because they can throw a false ratio error
- 3. Plug in and watch live data on a test drive, comparing the actual third gear ratio against the manufacturer's spec figure. A genuine mechanical slip shows the ratio drifting under load
- 4. Inspect the gearbox wiring and the main connector for corrosion, oil contamination, or chafing. ATF creeping up the loom into a sensor connector is a known troublemaker
- 5. Check for any TCM software updates or service bulletins for the model, then test the shift solenoids for correct resistance and operation
- 6. If fluid, sensors, wiring and solenoids all check out, the slip is internal. At that point you're looking at clutch packs or the valve body, and a transmission specialist needs to take it apart
Common questions about P0733
How long is the car off the road if it needs sorting? +
Depends entirely on what's behind it. A fluid and filter service is a half-day job at a garage. A solenoid or speed sensor swap is usually a day, sometimes less if access is decent. If the clutches inside have gone and the box needs stripping or replacing with a reconditioned unit, you're realistically looking at two to four days, longer if the specialist has to source a unit. Get the diagnosis nailed first so you're not paying for a box you didn't need.
Is a cheap aftermarket part worth fitting or should I go OEM? +
For speed sensors and solenoids, a decent quality aftermarket part from a reputable brand is fine and saves real money over a main dealer. Where I'd be careful is the gearbox itself. A no-name eBay 'recon' box with no history is a gamble, and you'll often pay twice when it fails. If the box is done, use a specialist with a proper rebuild warranty or a known reconditioner. Whatever fluid goes in must be the exact spec the box was designed for, no generic ATF, because the wrong fluid alone can cause slip.
Can I keep driving it like this? +
Short hops to get it diagnosed, yes. Carrying on regardless, no. A slipping clutch generates heat and shreds friction material into the fluid, which then circulates and wears everything else faster. You can turn a £200 solenoid job into a £1,500 rebuild by ignoring it for a fortnight. If it's dropped into limp mode, take that as the box protecting itself and book it in.
Will this fail my MOT? +
The MOT doesn't test how your gearbox shifts, so P0733 on its own won't fail you. The catch is the warning light. If the engine management lamp is glowing on the dash when the tester checks, that's a fail on the MIL, and on most cars a transmission fault will light it. Sort the underlying problem, clear the code, and make sure the light stays off before you book the test.
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 →