I replaced the transmission on my 1998 Chevy Astro Van.

Probably the transmission internal mode switch . But , without hooking up a scan tool an checking for DTC'S - diagnostic trouble codes an checking input data from the switch to the TCM - transmission control module i'd only be guessing . You don't want to waste money just replacing part's . Have a qualified repair shop check it out. Need factory service info an professional type scan tool .

Circuit/System Description
The transmission manual shift shaft switch assembly, also known as the Internal Mode Switch (IMS), is a sliding contact switch attached to the manual shift shaft inside the transmission case. The Park/Neutral Position (PNP) Switch is integrated into the IMS and connects to the Transmission Control Module (TCM) lead-frame through a short wire harness. The 5 inputs to the TCM from the transmission manual shift shaft switch assembly indicate the transmission gear selector lever position. This information is used for engine start enable, engine controls as well as determining the transmission shift patterns. The state of each input is available for display on the scan tool. The five input parameters represented are Signal A, Signal B, Signal C, Signal P (Parity), and Signal N (Park/Neutral Start Signal). Park/Neutral Signal is sent from the Park/Neutral switch directly to the Engine Control Module (ECM) and is used for engine start enable. The Park/Neutral Signal circuit is not connected to the TCM internally. The circuit uses the TCM as a pass-through connector only. The ECM Park/Neutral diagnostic monitors the Park/Neutral signal circuit to detect low voltage when the ECM expects high voltage and high voltage when the ECM expects low voltage.

DTC P1825: Internal Mode Switch - Invalid Range
DTC P182E: Internal Mode Switch - Invalid Range
DTC P1915: Internal Mode Switch Start/Wrong Range

is the selector lever engaging in the right place i'd have this checked as could be showing park but actually in neutral

On 1992 and later models, the neutral safety switch is incorporated into the Manual Lever Position or Transmission Range MLP/TR sensor.

RENOVAL & INSTALLATION

1. Disconnect the negative battery cable.
   
2. Raise and support the vehicle safely on jackstands.
   
3. Place the transmission in Neutral.
   
4. Remove and discard the manual control lever nut, then remove the lever from the transmission.
   
5. Detach the TR sensor electrical harness connector, remove the TR sensor retaining bolts, then pull the TR sensor off of the transmission case.
   

To install:

1. Position the TR sensor against the transmission case and loosely install the 2 retaining screws.
   
2. Attach the TR sensor electrical harness connector.
   
3. Use an alignment tool, such as the TR Sensor Alignment Tool T93P-70010-A, to align the TR sensor slots.
   
4. Tighten the TR sensor bolts to 80-100 inch lbs. (9-11 Nm).
   
5. Position the manual control lever onto the TR sensor, then install the new lever nut to 22-26 ft. lbs. (30-35 Nm).
   
6. Lower the vehicle.
   
7. Connect the negative battery cable.

ADJUSTMENT

Fig. : Adjusting the MLP sensor (click image for zoom)


Park is the last detent when the manual control lever is full forward. Return 2 detents toward the output shaft for Neutral.

1. Position the manual control lever in Neutral .
   
2. Raise the and safely support the vehicle.
   
3. Loosen the sensor retaining bolts.
   
4. Insert Gear Position Sensor Adjuster tool T93P-700 10-A or equivalent, into the slots.
   
5. Align all 3 slots on the MLP sensor with 3 tabs on the tool.
   
6. Tighten the attaching screws to 80-100 inch lbs. (9-11 Nm).
   
7. Lower the vehicle.

Hope this helps (remember to rating ans leave a testimonial commnet about this free answer).

So what it only does it in park or neutral ! The vehicle starting circuit is only suppose to let it start in park or neutal . Park neutral safety switch won't allow B+ voltage to S terminal on the starter solenoid unless the vehicle is in park or neutral . It's probably the starter relay contacts stuck closed . You really should learn how it works before guessing as to the problem . Plus learn automotive electrical testing ! The ignition switch when turned to the start position send's a voltage signal to the PCM - engine computer .The PCM will energize the starter relay to crank the engine . PCM / ABS 10amp fuse in the I/P fuse box supply's B+ voltage to the park / neutral safety switch . When in park or neutral the B+ voltage goes through the control side of the relay to the PCM which will supply a ground to energize the starter relay .

Neutral Safety/Back-up Light Switch

This is a combination switch which controls both Neutral Safety and Back-up lamp circuits.

C6 Transmission



C6 neutral start switch

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle on jackstands.
3. Remove the downshift linkage rod return spring at the low-reverse servo cover.
4. Coat the outer lever attaching nut with penetrating oil. Remove the nut and lever.
5. Remove the 2 switch attaching bolts, disconnect the wiring at the connectors and remove the switch.
6. Installation is the reverse of removal. Adjust the switch and tighten the bolts to 55-75 inch lbs. (6.2-8.5 Nm).
7. Remove the jackstands and lower the vehicle.
8. Connect the negative battery cable.

AOD Transmission



Removing the AOD neutral start switch

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle on jackstands.
3. Disconnect the wiring from the switch.
4. Using a deep socket, unscrew the switch.
5. Installation is the reverse of removal. Tighten the switch to 10 ft. lbs. (14 Nm).
6. Remove the jackstands and lower the vehicle.
7. Connect the negative battery cable.

4R70W Transmission




Removing the Manual Lever Position (MLP) sensor

As of 1994, the neutral safety switch is referred to as a Manual Lever Position Sensor (MLP).

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle on jackstands.
3. Disengage the harness connector from the MLP sensor.
4. Remove the 2 sensor attaching bolts and remove the sensor.

To install:

1. Install the MLP sensor and install retaining bolts. Do not tighten, the sensor requires adjustment.
2. Adjust the MLP sensor then tighten attaching screws to 80-100 inch lbs. (9-11 Nm).
3. Remove the jackstands and lower the vehicle.
4. Connect the negative battery cable.

ADJUSTMENT

C6 Transmission

1. Hold the steering column transmission selector lever against the Neutral stop.
2. Move the sliding block assembly on the neutral switch to the Neutral position and insert a 0.091 in. (2.3mm) gauge pin in the alignment hole on the terminal side of the switch.
3. Move the switch assembly housing so that the sliding block contacts the actuating pin lever. Secure the switch to the outer tube of the steering column and remove the gauge pin.
4. Check the operation of the switch. The engine should only start in Neutral and Park .

4R70W Transmission




Adjusting the MLP sensor

Park is the last detent when the manual control lever is full forward. Return 2 detents toward the output shaft for Neutral.

1. Position the manual control lever in Neutral .
2. Insert Gear Position Sensor Adjuster tool T93P-700 10-A or equivalent, into the slots.
3. Align all 3 slots on the MLP sensor with 3 tabs on the tool.
4. Tighten the attaching screws to 80-100 inch lbs. (9-11 Nm).

I hope help you. Good luck (rated this help).

try starting it in neutral,the neutral safety switch could be bad,its on the transmission linkage

im sorry to say no it will not.

try checking the park,neutral position switch

drop down relay in trans

replace the starter