P0720

P0720 is the output-side mirror of P0715: the TCM has lost or can't validate the signal from the Output Speed Sensor (OSS), which reads the final shaft speed feeding the driveshaft. The TCM uses OSS for vehicle speed (it's often the source the speedometer reads from on modern vehicles), for gear-ratio math (input RPM ÷ output RPM = actual ratio, compared against commanded ratio to detect slip), and for downshift scheduling. Lose it and you get a dead or erratic speedometer, harsh shifts, no TCC lockup, and often a limp-home default to a single gear. Fluid level and condition come first as always — but P0720 has a higher-than-usual rate of external causes because the OSS sits at the rear of the case, exposed to road debris and harness chafing where the trans meets the transfer case or driveshaft. Scan live data with the vehicle on a lift: in DRIVE, output RPM should rise smoothly with road speed (roughly 1,000 RPM per 25 mph on most trucks, but the exact ratio depends on final drive). A reading of 0 with the wheels turning is a dead sensor or open circuit; an erratic reading that jumps to redline values is usually a chafed harness shorting intermittently.

Vehicle-specific patterns: 2003-2010 Ford Explorer/Mountaineer/Ranger with the 5R55W/S throws P0720 from a failed OSS at the rear extension housing — the harness routing rubs the driveshaft slip yoke at suspension travel, $35 sensor + harness repair. 2007-2013 GM Silverado/Sierra 4WD trucks with the 6L80 throw P0720 when the transfer-case-to-trans wiring loom corrodes at the disconnect plug; cleaning and dielectric grease fixes it more often than replacing the sensor. 2005-2010 Honda Odyssey/Pilot with the 5AT (BGRA/BYBA) commonly throws P0720 from a known countershaft speed sensor failure — there's a Honda TSB and these were warranty-replaced under powertrain coverage on some VINs. 2008-2014 Nissan Altima/Murano with the JF016E CVT throws P0720 alongside a half-dozen other ratio codes when the CVT's pulley pressure sensors degrade — at that point you're looking at a CVT replacement, not a speed sensor. Estimated repair: $120 (sensor + harness) to $4,500+ (CVT replacement on the Jatco).