P0717: How to Diagnose & Fix — Input/Turbine Speed Sensor Circuit No Signal

The 722.9 7G-Tronic transmission conductor plate (internal electrical board with speed sensors) fails, causing limp mode, harsh shifting, and loss of gears. The electrical connector corrodes or the sensors crack from heat cycling.

The electronic conductor plate integrated into the 722.9 7-speed automatic's valve body (which houses the internal TCM, speed sensors and shift solenoids) is a widely reported failure on R171 SLKs equipped with the 7G-Tronic. As the plate's internal speed sensors and soldered joints degrade with heat cycling, the transmission drops into limp mode, typically locking into a single forward gear (often 2nd). The condition is temperature-sensitive and commonly appears from roughly 50,000-90,000 miles.

The 4T65E (and 4T65E-HD behind the supercharged L67) used in 1997-2005 Bonnevilles develops progressively harder 1-2 and 2-3 shifts as the PCM adapts to lengthening shift times, eventually setting P1811 (Maximum Adapt and Long Shift). Owners on GM Forum and the Pontiac Bonneville Club describe a slam-shift that appears after 20-30 minutes of driving, then becomes constant. Root causes identified by the community and rebuilders are broken 1-2/2-3 accumulator springs, a worn pressure control solenoid (PCS), worn Teflon sealing rings, and burned 2nd/3rd clutch material clogging shift and EPC solenoids. Pre-2003 units also have a non-hardened 4th-clutch shaft that wears its teeth. GM TSB 02-07-30-022B covers harsh shifts with multiple transmission DTCs on 2000-2004 Bonnevilles, and TSB 04-07-30-028 covers fluid leaks from a reverse-servo seal that shrinks below 20F.

Behind the Northstar, the 2004-2005 GXP uses the Cadillac 4T80E. Owners in GM Forum's GXP section report the second most common GXP failure after head gaskets: an internal torque converter seal that shrinks or tears, producing a rumble-strip shudder at light throttle around 35-45 mph in 4th with the converter clutch applied, temporarily relieved by a light brake-pedal touch or cancelling overdrive. Left alone the converter clutch burns and the transmission starts slipping. The 4T80E input speed sensor is also a frequent failure that sets P0716/P0717 and forces limp mode; because it sits inside the case, it is normally replaced during the converter job. GM issued a bulletin on a 4T80E torque converter design change for 2005 DeVille and Bonneville.

Equinox models with the GM 6T70/6T75 six-speed automatic suffer shudder, harsh or delayed shifts, slipping, and loss of reverse. A common root cause is failure of the 3-5-reverse wave plate, which can crack and cause extreme shudder when reverse is engaged and eventual loss of drive. Overheated/degraded fluid that loses viscosity accelerates internal wear. Failures typically appear between roughly 60,000 and 150,000 miles. Owners report bucking when engaging gear, failure to shift out of 2nd, and inability to engage reverse.