Code P0730: incorrect gear ratio in the automatic gearbox

Original definition (SAE J2012): Incorrect Gear Ratio^[1][2]

• P0730Incorrect gear ratio: the actual gearbox ratio does not match the one corresponding to the commanded gear.
• P0731Incorrect ratio in 1st gear.^[5][7][8]
• P0732Incorrect ratio in 2nd gear.^[9][10]
• P0733Incorrect ratio in 3rd gear.^[11][12]
• P0734Incorrect ratio in 4th gear.^[13][14]
• P0735Incorrect ratio in 5th gear.^[15][16]

1. 1Low, dirty, burnt or contaminated gearbox oil (ATF), which does not allow the pressure needed to hold the gears to be maintained. It appears in all the sources and is the first thing to check.^{[1][2][3][4][17]}
2. 2Faulty shift solenoids or ones with damaged wiring.^[1][3][4]
3. 3Valve body with a valve stuck or blocked (often by debris), or a blocked hydraulic control circuit.^[1][3][4]
4. 4Internal mechanical wear: worn clutches and bands, leaking clutch seals, broken springs or damaged gearbox parts (gears, bearings).^{[1][3][4][17]}
5. 5Faulty input and output speed sensors, which send wrong data to the control unit.^[2][3]
6. 6Blocked oil filter, worn pump or torque converter lock-up clutch locked (CódigosDTC).^[1]
7. 7Electrical faults: corroded connectors, damaged wiring or a faulty gearbox control unit.^[1][3][17]

• Engine fault warning light on, often with the gearbox in limp mode or forced into neutral.^[1][3][4]Engine warning light: faults that cause it
• Limp mode: the gearbox stays in one gear or drops to neutral; in some cases it corrects itself after restarting the engine.^[3]Limp mode: faults that cause it
• Abrupt, delayed or absent shifts, and weak acceleration.^[1][3][17]Gears will not engage: faults that cause it
• Gearbox slipping: the revs rise but the speed does not follow, or a revs flare between gears.^{[1][3][4][17]}
• Higher fuel consumption.^[1][3][17]Uses more fuel: faults that cause it
• In some cases no noticeable symptom at all (Rerev).^[17]

1. 1Read the codes from all the control units (not only the engine one) and look at the freeze frame data. Deal first with any ABS, speed sensor, solenoid or electrical code, and check whether there is a specific gear code (P0731 to P0735): it indicates the gear in which the ratio is failing.^[2][3][4]
2. 2Check the level and condition of the gearbox oil: colour, burnt smell and debris. Fix any leaks and, if it is degraded or contaminated, change it (with the filter) according to the manufacturer.^{[1][3][4][17]}
3. 3With diagnostic equipment, plot the input and output speeds during gear changes and compare the ratio obtained with the expected one for each gear; or compare engine speed with the calculated output speed.^[1][3]
4. 4Check the gearbox speed sensors, the wiring, the connectors of the gearbox control unit and its power supplies and earths before replacing any module.^[1][3][4]
5. 5Carry out an oil pressure test and check the solenoids (a workshop test with suitable equipment).^[17]
6. 6If the fault persists, open the sump: inspect the filter and the valve body and then the clutches and internal parts. For the torque converter, CódigosDTC proposes a speed test using the manufacturer's references. Replacing or reprogramming the gearbox control unit is only considered once all of the above has been ruled out.^[1][3]