98 1500 Speedo/tranny Problems?

[nsgmc]

So I have a 96 1500 4X4 ext. cab, it is an automatic with a 305 and as of today something is going wrong. While I am driving all of the sudden the speedo goes dead (falls off back to zero normally) and then WHAM comes back up to speed and a way I go. Seems to happen in the 40 mph area mostly. When this happens it is almost like it is slipped into neutral. Please help me with this before I have just a parts truck LOL.

[Nytemare]

So I have a 98 1500 4X4 ext. cab, it is an automatic with a 305 and as of today something is going wrong. While I am driving all of the sudden the speedo goes dead (falls off back to zero normally) and then WHAM comes back up to speed and a way I go. Seems to happen in the 40 mph area mostly. When this happens it is almost like it is slipped into neutral. Please help me with this before I have just a parts truck LOL.

Sounds like a vehicle speed sensor issue.

[nsgmc]

Is there any type of test you can do on these? Seems they are not a cheap part to replace.

[Nytemare]

Is there any type of test you can do on these? Seems they are not a cheap part to replace.

It should throw a code, but not always. I would think that a scan tool like the tech 2 could do a real time test of the sensor, but it would have to happen with a tech in the vehicle and the tool connected to the ECM.

 

 

I would get up under the truck and check that its securely mounted and that the wires are not screwed up

[nsgmc]

Is there any type of test you can do on these? Seems they are not a cheap part to replace.

It should throw a code, but not always. I would think that a scan tool like the tech 2 could do a real time test of the sensor, but it would have to happen with a tech in the vehicle and the tool connected to the ECM.

 

 

I would get up under the truck and check that its securely mounted and that the wires are not screwed up

 

 

 

So I got under it and took the speedo sensor out, cleaned it up looked at wires and thought for shits and giggles I'd check the fluild level. One full litre low! Topped it up and took it for a drive, it worked the whole time. Would this low fluid level caused the issue?

[Nytemare]

Is there any type of test you can do on these? Seems they are not a cheap part to replace.

It should throw a code, but not always. I would think that a scan tool like the tech 2 could do a real time test of the sensor, but it would have to happen with a tech in the vehicle and the tool connected to the ECM.

 

 

I would get up under the truck and check that its securely mounted and that the wires are not screwed up

 

 

 

So I got under it and took the speedo sensor out, cleaned it up looked at wires and thought for shits and giggles I'd check the fluild level. One full litre low! Topped it up and took it for a drive, it worked the whole time. Would this low fluid level caused the issue?

 

Fluid level should have nothing to do with the speed sensor...but having it covered in crap would have.

[nsgmc]

Really not much crap on it, I will drive it some more and see what happens. Looks like a new rear seal will be in order.

[Nytemare]

Really not much crap on it, I will drive it some more and see what happens. Looks like a new rear seal will be in order.

yeah, you could have a wire going bad too....the moving around you did may have pushed the break back together.

 

Yeah...see what happens

[nsgmc]

yeah, you could have a wire going bad too....the moving around you did may have pushed the break back together.

 

Yeah...see what happens

 

 

 

Oh don't put that hex on me LOL, me and broken wires are not a good pair, could end up being a parts truck . Thanks for your help thus far.

[Nytemare]

yeah, you could have a wire going bad too....the moving around you did may have pushed the break back together.

 

Yeah...see what happens

 

 

 

Oh don't put that hex on me LOL, me and broken wires are not a good pair, could end up being a parts truck . Thanks for your help thus far.

LOL...you can buy an entire replacement harness for that sensor...its not expensive.

[nsgmc]

OK so days later with all well and good, got in the ol truck to head to work............ NO SPEEDO! Should there be a check light coming on, what do I look for? Is there a voltage I can check when I un plug the sensor or a check to see if the sensor is working? I am now officially frustrated.

[Nytemare]

OK so days later with all well and good, got in the ol truck to head to work............ NO SPEEDO! Should there be a check light coming on, what do I look for? Is there a voltage I can check when I un plug the sensor or a check to see if the sensor is working? I am now officially frustrated.

Its just a magnetic pick-up so holding a piece of metal on the end that goes in the trans should make the magnetic switch close and complete the circuit and you should read a very low resistance on two of the wires that are connected to the switch. I do not know which wires to read though, it should be a 3 or 4 wire sensor.

[nsgmc]

OK so days later with all well and good, got in the ol truck to head to work............ NO SPEEDO! Should there be a check light coming on, what do I look for? Is there a voltage I can check when I un plug the sensor or a check to see if the sensor is working? I am now officially frustrated.

Its just a magnetic pick-up so holding a piece of metal on the end that goes in the trans should make the magnetic switch close and complete the circuit and you should read a very low resistance on two of the wires that are connected to the switch. I do not know which wires to read though, it should be a 3 or 4 wire sensor.

 

 

There are only two wires going into the switch, are thet both "live" if I disconnect the switch while the truck is running?

[Nytemare]

OK so days later with all well and good, got in the ol truck to head to work............ NO SPEEDO! Should there be a check light coming on, what do I look for? Is there a voltage I can check when I un plug the sensor or a check to see if the sensor is working? I am now officially frustrated.

Its just a magnetic pick-up so holding a piece of metal on the end that goes in the trans should make the magnetic switch close and complete the circuit and you should read a very low resistance on two of the wires that are connected to the switch. I do not know which wires to read though, it should be a 3 or 4 wire sensor.

 

 

There are only two wires going into the switch, are thet both "live" if I disconnect the switch while the truck is running?

 

Whats the drop across the sensor?

 

Its an electromagnet, in other words its a coil, so you should see under 1000Ohms of resistance across both terminals of the sensor...disconnected obviously.

 

A parts shop should let you meter a new sensor if they have one in stock....just to see if the readings are the same.