Is it common for the CEL to come on only when I shift (auto) from Park to Reverse or Drive and vice versa? It only seems to do it if I shift semi-quick, but not all the time and it only comes on for a brief second. Also, is this anything that will make me fail inspection next month?

 

Your state laws will determine if that's enough to fail you, but it shouldn't take much time or money to fix it.

Do you have the E4OD transmission (code E on the door sticker)?



If so, the old MLPS (Manual Lever Position Sensor, aka neutral safety switch) has been identified as having a water intrusion problem, and it was redesigned. You can get a replacement at any parts store, and it should include a new connector shell. You have to disassemble your original connector & transfer the wires to the new shell, but it's not hard.

 

Looks like the door sticker was removed at some point (didn't notice until I just checked) Is there a way to check tranny type on the VIN number?

Also, where is this sensor, and do you have a part# for it? I'm having trouble finding one online.

 

No, the transmission isn't coded in the VIN. You can ID slushboxes by the shape of the pan, but I don't have that diagram. It should come up if you do some Googling.

The MLPS is on the L side of the trans, around the shift lever. At the bottom of the 2nd page of this thread, you can read the TSB about the MLPS. This diagram is a different transmission, but the MLPS is the same as the Digital Transmission Range (DTR) sensor at the bottom center.

 

'91 you didn't say what motor, but the three possible choices are the...

C6, PRND21, 17 pan bolts
AOD, PRN(D)D1, 14 pan bolts
E4OD, PRN(D)21, 20 pan bolts, OD lockout button on the dash.

Adrianspeeder

 

I do have an OD button on the dash, haven't gotten under the truck to see if there are 20 pan bolts. At least I don't have to lift it to do this work

 

The O/D OFF button is enough to ID it as the E4OD. The only other truck trans that used it was the 4R70W, but it wasn't used until '94.