SERVICE MANUAL UPDATE SEC. 7A TRANSAXLE DOWNSHIFT SYSTEM
Subject: AUTOMATIC TRANSAXLE DOWNSHIFT SYSTEM
Model and Year: 1990-91 GEO STORM
TO: ALL CHEVROLET DEALERS
Base model GEO Storm vehicles equipped with automatic transaxles incorporate a switch and a solenoid (rather than a kickdown cable) for the purpose of downshifting during hard acceleration. These components have not, as yet, been covered in any of the existing GEO Storm service publications. Therefore, this bulletin has been written as an addition to Section 7A-l of the 1990 and 1991 GEO Storm Service Manuals (ST371-90 and ST371- 91).
AUTOMATIC TRANSAXLE DOWN SHIFT SYSTEM
GENERAL DESCRIPTION
All 1990 and 1991 GEO Storms, equipped with the KF400 three speed automatic transaxle, incorporate an automatic transaxle downshift system. This system consists of fuse C-11, a kickdown switch, a kickdown solenoid and a kickdown valve. Fuse C-11 is located in the fuse block, the kickdown switch is attached to the accelerator pedal bracket, the kickdown solenoid is screwed into the transaxle and kickdown valve is integral to the transaxle.
During cruise conditions, when throttle angle is changed sufficiently to cause a 3-2 downshift (or a 2-1 downshift), the accelerator pedal strikes the plunger on the kickdown switch. When the plunger is pressed down, the switch closes and applies battery voltage through fuse C-11 and the kickdown switch to the kickdown solenoid. When battery voltage is applied, the kickdown solenoid energizes and opens the kickdown valve in the transaxle. With the kickdown valve opened, hydraulic pressure is rerouted to either the 2nd-3rd or lst-2nd shift valve, causing the appropriate downshift to occur.
DIAGNOSIS
True diagnosis of the automatic transaxle downshift system can only be performed during a road test. During the road test, while cruising in the "D" (DRIVE) range (2nd and 3rd gears), check to see that the 3-2 and 2-1 downshifts occur within the engine vacuum/ vehicle speed limits detailed in the Transaxle Shift Schedule Diagram (Figure 2).
If downshifts occur, but not at the prescribed vehicle speeds, refer to Section 7A-l of the 1990 or 1991 GEO Storm Service Manual for further transaxle diagnosis procedures.
If downshifts do not occur, perform the following diagnostic procedures:
1. Check fuse C-1 1 with a fuse tester. Replace as required.
2. Turn the ignition switch to "ON." Backprobe the kickdown switch connector with a J 340029-A digital multimeter from the BLK/YEL wire to a known good ground. Measure voltage.
* If no voltage is present, repair open (s) in the BLK/YEL wire between the fuse block and the kickdown switch.
* If voltage is present, proceed to step 3.
3. Slowly press the accelerator pedal down by hand until a clicking sound is heard from the kickdown switch.
* If no click is heard, hold the accelerator pedal down and readjust the switch by loosening the locknut and rotating the switch in a clockwise direction until a click is heard. Rotate the switch an additional one-half turn clockwise past the point where the click was heard and retighten the locknut.
* If a clicking sound can not be obtained by readjustment, replace the kickdown switch.
* If a clicking sound is heard when the accelerator pedal approaches wide-open throttle, proceed to step 4.
4. Backprobe the kickdown switch connector with a J 34029-A digital multimeter from the BLU/WHT wire to a known good ground. Measure voltage with the accelerator pedal pressed to the wide-open throttle position.
* If no voltage is present, replace the kickdown switch.
* If voltage is present, proceed to step 5.
5. Backprobe the kickdown solenoid connector with a J 34029-A digital multimeter from the BLU/WHT wire to a known good ground. Measure voltage with the accelerator pressed to the wide-open throttle position.
* If no voltage is present, repair open (s) in the BKU/WHT wire between the kickdown switch and the kickdown solenoid.
* If voltage is present, proceed to step 6.
6. Remove the kickdown solenoid connector. Connect a J 34029 - A digital multimeter from the solenoid terminal to a known good ground. Measure resistance.
* If resistance is not between 3.2 and 3.7 ohms, replace the kickdown solenoid.
* If resistance is between 3.2 and 3.7 ghms, the automatic transaxel downshift system is operating correctly. Refer to Section 7A-1 of the 1990 or 1991 GEO Storm Service Manual for further transaxle diagnostic procedures.
ON-VEHICLE SERVICE
KICKDOWN SWITCH
Figure 3
Remove or Disconnect
1. Kickdown switch electrical connectors.
* Loosen kickdown switch locknuts.
2. Kickdown switch from accelerator pedal bracket by rotating the switch counterclock- wise.
Install or Connect
1. Kickdown switch to accelerator pedal bracket by rotating switch clockwise until a click is heard. Rotate the switch an additional one-half turn clockwise after the click is heard.
* Tighten the kickdown switch locknuts.
2. Kickdown switch electrical connectors.
Figure 4
Remove or Disconnect
1. Kickdown solenoid electrical connector (under RH side of battery tray).
* Raise and suitably support vehicle. Refer to Section OA in the 1990 or 1991 GEO Storm Service Manual.
2. Kickdown solenoid from transaxle by rotating counterclockwise.
3. Kickdown solenoid 0-ring.
Install or Connect
1. New kickdown solenoid 0-ring.
2. Kickdown solenoid to transaxle by rotating clockwise.
* Lower vehicle.
3. Kickdown solenoid electrical connector (under RH side of battery tray).
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
