P0730

P0730 means the TCM has calculated an actual gear ratio (input RPM ÷ output RPM) that doesn't match any of the commanded ratios for the gear it thinks it should be in, but the TCM can't tell which gear specifically is wrong — so it sets the generic 'incorrect ratio' code. This is the canary in the coal mine for internal trans wear: clutch slippage, band wear, a stuck pressure-control solenoid letting line pressure droop, or fluid-level/quality problems aerating the pump. Fluid check is non-negotiable here — burned or low fluid is the cause more often than any single internal component on a P0730. Once fluid is verified, the next live-data check is line pressure with a gauge tap'd into the test port: at idle in DRIVE most automatics want 60-90 psi; at wide-open throttle in 1st you want to see 180-240 psi depending on application. Low line pressure under load with good fluid points to the pressure-control solenoid (cheap external fix) or to internal seal leakage (rebuild territory). Note that a slipping torque converter clutch can mimic P0730 by creating an apparent ratio mismatch even when the gearset is fine — that's why P0741 has to be ruled out before condemning hard parts.

Vehicle-specific patterns: 2003-2010 Honda Accord/Odyssey V6 5AT is the textbook P0730 vehicle — the 3rd gear clutch pack wears out, the trans slips, ratio math goes wrong, and Honda issued multiple TSBs and a class-action settlement on certain VIN ranges (BAYA/MGFA codes); fluid changes early extended life but rebuilds are common past 130k miles. 2004-2008 Chrysler/Dodge with the 42RLE (Wrangler, Liberty, 300) throws P0730 from a failed overdrive solenoid causing the overdrive band not to apply — external solenoid fix, not a rebuild. 2007-2013 GM 6L80 throws P0730 when the 3-5-Reverse waveplate fractures (a known internal failure mode) — this one IS a rebuild. 2006-2012 Ford with the 6R80 (F-150, Expedition) commonly throws P0730 from a stuck pressure-control solenoid in the lead-frame; a $400 solenoid body swap fixes what would otherwise look like a rebuild. Estimated repair: $250 (external solenoid + filter) to $4,800+ (full rebuild on the Honda 5AT).