If your Vehicle has....Harsh 1-2 Shifts.....and you have your Vehicle Scanned and Trouble Code.....P1870...Appears...the Below Link may apply to your Vehicle This is a G.M. Service Bulletin.... TSB # 01-07-30-023A Harsh 1-2 Up-shift, SES, MIL, or CEL Illuminated, DTC P1870 Set (Replace Control Valve Body) 1996 Buick Roadmaster 1996 Cadillac Fleetwood 1999-2000 Cadillac Escalade 1996-2000 Chevrolet Camaro, Corvette 1996-2000 Pontiac Firebird 1996-2000 Chevrolet and GMC Light Duty Truck Models 1996-2000 Oldsmobile Bravada with 4L60-E Automatic Transmission (RPO M30) Built Prior to January 15, 1999 (Julian Date 9015) This bulletin is being revised to update the Parts Information Please discard Corporate Bulletin Number 01-07-30-023 (Section 07 -- Transmission/Transaxle). CONDITION, .......Some customers may comment on a harsh 1-2 up-shift and the Check Engine Light or Service Engine Soon indicator is illuminated. Diagnosis, .......Typically, these vehicles will have been driven more than 32,000 km (20,000 mi) before this condition occurs. .......The scan tool may show a DTC P1870 set as a history code. ........A Harsh 1-2 Shift or DTC P1870, caused by wear in the..."Control Valve Body", may be difficult to duplicate when the transmission temperature is below 93°C (200°F). CAUSE, ......The condition may be due to wear in the control valve body. This wear occurs in the bore that contains the TCC isolator and regulator valves, and results in poor, or no, TCC apply IMPORTANT, ......DTC P1870 is a type B code. The conditions for setting the P1870 DTC must occur on TWO CONSECUTIVE TRIPS (ignition cycles, with a drive cycle) before setting a P1870 history code. ......When the conditions for setting DTC P1870 are met (first trip), the PCM commands maximum line pressure and harsh 1-2 shifts are the result. ......This may result in a harsh 1-2 shift with no history code if the conditions for setting the DTC required for the second trip are not met, on two consecutive trips (Ignition cycles, with a drive cycle). ......When the conditions for setting the DTC are met, on the second consecutive trip, a DTC P1870 is stored as a history code. ......When the P1870 code is stored, the PCM will turn on the Service Engine Soon (SES), ......Check Engine Light (CEL), or Malfunction Indicator Lamp (MIL). CORRECTION, Install a control valve body with the revised TCC regulator and isolator valves. These valves are used in all transmissions produced after January 15, 1999 (Julian Date 9015), and all of the service parts currently available through GMSPO contain revised TCC regulator and isolator valves. Also, ......If all of the following conditions are true, it is not necessary to Rebuild the transmission or to replace additional transmission components beyond the "Control Valve Body". .......Transmission operation is normal before the transmission reaches operating temperature, or before DTC P1870 is set (no slips, flares, or missing gears). ......The torque converter is not blue or overheated. ......The transmission fluid is not burned or has no burned odor. ......The transmission fluid pan contains no abnormal debris (clutch material, bronze, brass, or metal fragments).