Okay so I have a1996 Blazer LS four-wheel drive. It has 214,000 miles. It will not shift out of first gear and the ABS light comes on after driving a few mph. (3-5 mph)?? The speedometer and odometer do not work.

I did have the vehicle speed sensor code, it is not coming on now.
P0502
Control unit:10
Vehicle speed sensor (VSS) - low input


Current DTC code:
P0102
Control unit:10
Status: Confirmed
OBDII: Mass air flow (MAF) sensor/volume air flow (VAF) sensor - low input

ABS codes:
Current:
C1236
Issue in Low System Supply Voltage

History:
C1265
Issue in Left Rear Inlet Valve Solenoid
C1268
Issue in Right Rear Outlet Valve Solenoid
C1281
VSES Sensors Uncorrelated
C1286
Issue in Steering Sensor Bias

I currently have fuse # 2 and # 11 pulled because the battery keeps going dead. My history with the vehicle: it was sitting for about 2 years before I got it. I had the fuel pump replaced, new fuel filter, new battery and changed the oil. When I first got it the horn worked, one time I hit it and it kept going off after I had pressed it. It quit working at some point and I never looked into fixing it. I ended up towing a vehicle and I bought a adapter for the trailer lights. After that, the door ajar tone (when the key is in the ignition) did not work, which I didn't mind because it's really annoying. It started working again just recently. When I was driving and would turn left, there was a clicking noise coming from one of the front wheels. Somebody said it was the CV joint or something that was going out? It does not do that any more. There's something going on electrically that keeps draining the battery. I thought it was a door ajar switches, that it wasn't telling that the doors were closed and it would leave the interior lights on. I just pulled the courtesy lights fuse (fuse # 2). I recently put it back in and the passenger side light near the floorboard would not turn off even the doors were closed I didn't go and check all the doors and close them again to make sure the switches were working I just pulled the fuse again. Someone had disconnected the driver side mirror light on the visor. I'm not sure what was going on there. An aftermarket stereo had been installed and I had taken out the remote wire that was ran from the battery to the back of the vehicle when it was not working and parked. Whoever installed the stereo had went through a weird spot through the wheel well instead of the firewall. There are so many electrical connectors from the radio to the vehicle harness in the dash. Also in the steering column underneath the dash there was something that was wired in like a GPS or an alarm system or something at one point. Somebody cut some wires and left wires exposed underneath the dash. The vehicle does have a leak in the driver side door, close to the fuse box causing corrosion. I did take out all the fuses and clean them and put them back and I've replaced some them. One time I put the cigarette lighter in and it blew the fuse. The heater fan makes a noise too. But then there's a couple weird noises coming from the middle of the dash and from the instrument panel, steering column area. I don't believe the four wheel drive light on the dash buttons ever worked since I've had the vehicle. I know the 4x4 was engaging not too long ago. There are two wire harnesses on the outside passenger bottom frame that are kind of hanging over the frame. It seems like they should be up underneath the vehicle more. There's currently water coming down on the passenger side upper door, going down the door panel to the floor. It actually soaked the whole seat and floorboard. I'm aware that there is something relating to the ABS system (I think) that's hidden underneath the carpet there. So the ashtray.. I was trying to get it back in or just take it out. It was stuck and then when I was touching the metal little clip thing that holds the ashtray in, one of the weird dash sounds stopped. By wiggling the ashtray around it started, stopped the noise. Seems like a loose connection in the wires located behind the ashtray area. I don't know if the cruise control works or ever worked because I never used it. It's now leaking transmission fluid from somewhere underneath the vehicle. A friend saw that the rear differential was low on gear oil and added some. Also low on brake fluid and added some of that.

I've tried searching for a diagram for all of the ground locations, at least for the engine, but my brain's about to pop and I could not find any. I know there's two that are by the battery near the radiator. I changed out the battery terminal connectors and had to relocate one of those ground wires because the bolt holding it on was stripped. I just need to pinpoint whatever I'm doing because I have to get somebody to help me. I do have a multimeter and the light up the circuit tester, an OBD-II scanner and a couple apps. Where do I start?

 

Water intrusion, that's first place to resolve. There are too many circuits involved in the places you mentioned that got wet that will have you chasing your tail. Are you able to work on the truck in a dry location like a garage in the meantime until you get the water intrusion resolved?

Go to my.alldata.com and buy a subscription for your specific vehicle. It’s only like $60 for a year and will give you the Technical Service Manuals, OE wiring diagrams as well as colored wiring diagrams, TSB’s, troubleshooting procedures, etc.

P0502 will put the truck into limp mode (2nd gear only). Alldata will also provide all test procedures for this fault to narrow down the issue to a faulty sensor or circuit issue. Unless someone here has it for a ’96. I there were some differences with the pre-’98 trucks in general.

Is the aftermarket stereo still installed? If so, I would pull it out for now. Hopefully whoever put it in didn’t cut the truck-side harness connector off, hopefully they used an interface. I don’t know about a ’96, but as an example one wire that goes to the stereo in a ’98 involves the VSS circuit. Also that same wire connects at a splice pack in front of the ash tray. I would start disassembling that area to do some visual inspections of the splice pack/wires.

What kind of shape is the braided ground strap between your engine and the firewall on the passenger side? Trace your B(-) cable down to where it connects to the engine. Inspect and clean as needed.

Generally you start with the lowest numbered codes first, but personally I think I might clear the codes next to see if that P0502 pops up again as “Current” before I worried about P0102. I’m thinking that there is a short issue in the cab that is your main concern for now. Either way, solving the VSS issue should get you shifting again. That’d be my first priority.


EDIT: Right after you clear the codes (if you decide to go that route) disconnect the battery, then depress your brake pedal for a few to unload any stored energy. Reconnect your battery and start from there. Personally, when I have a vehicle that someone has added mods and am having problems I like to get it back to OEM so I have a clean slate to work with.