99 Pontiac Grand Prix gtp

[skatey]

I wanted to ask you a couple questions regarding the vss system, so a couple days ago my Spedo started to jump and the transmission shifts gears while it’s jumping, I’ve replaced the speed sensor on the transmission then I noticed a small cut on the pigtail and put a new one on there too. The problem continued so I checked my abs connectors and cleaned them up and it seemed to get better but still was messing up, now when I let off the thottle that seems to be the time that the car likes to go crazy and usually blipping the gas helps set it back to normal but earlier it seemed to throw itself into neutral and when I pushed the gas the power wasn’t transferring to the wheels when I was moving and the speedometer said 0. I’m having a hard time diagnosing this because I’ve done everything I could have thought of and talked to others about it. What I believe lead to this was an undercarriage wash and maybe water crawled its way up. Now where, I have no clue. If you have some input to throw in that would be helpful. The video attached is only part of what’s happening but it’s around when it started.

[94 olds vert]

Any codes? For the engine or transmission? Have you checked the transmission fluid? Is it low?

I would check your battery cables, and make sure the ground wire is clean. A bad ground wire can cause all sorts of issues. 

Edited August 22 by 94 olds vert

[skatey]

1 hour ago, 94 olds vert said:

Any codes? For the engine or transmission? Have you checked the transmission fluid? Is it low?

I would check your battery cables, and make sure the ground wire is clean. A bad ground wire can cause all sorts of issues. 

No there’s not any codes which is the weird part, the transmission fluid is also full. I have a feeling maybe the battery is going bad but there’s no corrosion or anything like that.

[94 olds vert]

45 minutes ago, skatey said:

No there’s not any codes which is the weird part, the transmission fluid is also full. I have a feeling maybe the battery is going bad but there’s no corrosion or anything like that.

You might want to drop the transmission pan and inspect. My 06 Silverado was doing weird stuff right before the transmission failed. 

A failing battery or alternator can cause issues. A multimeter is helpful with that as these cars dont have a Volt gauge. 

[skatey]

54 minutes ago, 94 olds vert said:

You might want to drop the transmission pan and inspect. My 06 Silverado was doing weird stuff right before the transmission failed. 

A failing battery or alternator can cause issues. A multimeter is helpful with that as these cars dont have a Volt gauge. 

I tested the battery at 12.2 when off and 14.4 when on same with the alternator.

[Black92GS]

I have my doubts that the battery or it's connections are the issue.  In my experience with these cars, you start seeing the typical weak battery symptoms long before you begin experiencing any real drivability issues. 

For starters, you can try disconnecting the VSS sensor altogether.  This should throw a code for the VSS circuit itself, and should also put the vehicle in some sort of limp mode.  At the very least, it should help prove that the circuit itself is good and that it can set a code for it. If you drive the car with it unplugged, just make sure to route the wire somewhere it won't be damaged.

I would then start checking the wiring to the VSS as best as possible.  If the issue started after getting the underside of the vehicle wet, it could be something as simple as the wires having rubbed through and got wet, or possibly water intrusion into the VSS connector itself causing corrosion between the terminals. It's hard to tell in the video...but it seems like the speedometer acting up coincides with hitting bumps. Running the vehicle in the could allow you see if it remains stable, or if the issue persists. I have heard of instances of the reluctor wheel inside the trans (what the VSS reads) either getting damaged or becoming loose and moving around.  That could definitely cause intermittent speed sensor output.   

If all of that checks out...The Ivan (PHAD) and Eric O (SMA) in me is thinking you need a scope to really know what is going on here...as the issue could ultimately be anything from a defective new sensor, to a pin fitment issue at a connector in that circuit, to a broken/damaged wire up to the PCM....to corrosion somewhere along the wire/connector...to a loose/damaged reluctor wheel inside the trans....to a corrupt PCM itself. 

[skatey]

23 minutes ago, Black92GS said:

I have my doubts that the battery or it's connections are the issue.  In my experience with these cars, you start seeing the typical weak battery symptoms long before you begin experiencing any real drivability issues. 

For starters, you can try disconnecting the VSS sensor altogether.  This should throw a code for the VSS circuit itself, and should also put the vehicle in some sort of limp mode.  At the very least, it should help prove that the circuit itself is good and that it can set a code for it. If you drive the car with it unplugged, just make sure to route the wire somewhere it won't be damaged.

I would then start checking the wiring to the VSS as best as possible.  If the issue started after getting the underside of the vehicle wet, it could be something as simple as the wires having rubbed through and got wet, or possibly water intrusion into the VSS connector itself causing corrosion between the terminals. It's hard to tell in the video...but it seems like the speedometer acting up coincides with hitting bumps. Running the vehicle in the could allow you see if it remains stable, or if the issue persists. I have heard of instances of the reluctor wheel inside the trans (what the VSS reads) either getting damaged or becoming loose and moving around.  That could definitely cause intermittent speed sensor output.   

If all of that checks out...The Ivan (PHAD) and Eric O (SMA) in me is thinking you need a scope to really know what is going on here...as the issue could ultimately be anything from a defective new sensor, to a pin fitment issue at a connector in that circuit, to a broken/damaged wire up to the PCM....to corrosion somewhere along the wire/connector...to a loose/damaged reluctor wheel inside the trans....to a corrupt PCM itself. 

While working on the sensor i had noticed a small cut in the rubber where the sensor pigtail was and wired a new one to the harness because the cut was too close to the male end to rewire the old one. Also bumps tend to cause it to freak out because I first started seeing symptoms when I was using cruise control and hit a big enough bump it would shut off. Now I did try looking into the pcm but I couldn’t find a diagram that would show me where they ran into it and I’m also not the best at reading them. So far I’m only thoughts left on this are it’s the pcm or as you mentioned the reluctor wheel is loose and not giving accurate readings. I don’t have the funds to take this car to the shop and I’ve always done the work myself so I’m working with what I can, I do appreciate the help.

[skatey]

Just now, skatey said:

While working on the sensor i had noticed a small cut in the rubber where the sensor pigtail was and wired a new one to the harness because the cut was too close to the male end to rewire the old one. Also bumps tend to cause it to freak out because I first started seeing symptoms when I was using cruise control and hit a big enough bump it would shut off. Now I did try looking into the pcm but I couldn’t find a diagram that would show me where they ran into it and I’m also not the best at reading them. So far I’m only thoughts left on this are it’s the pcm or as you mentioned the reluctor wheel is loose and not giving accurate readings. I don’t have the funds to take this car to the shop and I’ve always done the work myself so I’m working with what I can, I do appreciate the help

[Black92GS]

If it seems to be affected by bumps, I wouldn't come close to condemning the PCM just yet. Checking the reluctor wheel should be as simple as pulling the VSS and reaching inside the hole with your finger.  You should be able to touch the reluctor just enough to be able to feel for any play.  It's supposed to be tight and should only want to move along with the rest of the diff. If it feels like you can move it around without much effort...then you have an idea of where to look next.  At least pulling the diff on 4t65e can be done by a single person, with the trans in the car using fairly basic tools.

If that checks out, you could re-install the VSS and try running the vehicle up in the air and seeing what happens.  If the speedometer reading seems fairly stable, you could carefully try playing around with the wire while it's running in the air to see if you can cause it to act up.

The reluctor is the silver toothed thing on the right side, and the hole for the VSS would be in the differential carrier directly above it.  

[Schurkey]

8 hours ago, skatey said:

I tested the battery at 12.2 when off and 14.4 when on same with the alternator.

12.2 volts means the battery is half-dead.  CHARGE THE BATTERY and see what happens.  A slow-charge overnight would probably be best.

A "12-volt" battery when fully-charged should show 12.6--12.8 volts AFTER the battery has been off the charger for an hour or two.  This somewhat depends on the battery temperature--higher temperature leads to higher voltage; freezing-cold will produce low voltage.  The battery might show 13+ volts directly off the charger, but the excess is "surface charge" that will self-dissipate if left alone for awhile, or it can be removed with a 50 amp load for five or ten seconds.

[Schurkey]

5 hours ago, Black92GS said:

I have my doubts that the battery or it's connections are the issue...

...If all of that checks out...The Ivan (PHAD) and Eric O (SMA) in me is thinking you need a scope to really know what is going on here.

It's good diagnostic procedure to verify the battery and cables/fuses/fusible links etc., early-on in the process.  We know the battery is not properly charged, perhaps actually defective.  It's worth a shot.  Besides...corrosion in the battery cables can be hidden under the insulation, or behind the "sealed" side-terminal cable ends.

A 'scope is a useful tool, but in this case I'd be connecting a decent scan tool with graphing capability.  You'd get the same graphic representation of the various sensor signals as with a 'scope, but better in that you know the computer is actually receiving what the sensors are sending.  And you could verify EVERY sensor with a scan tool in the time it takes to back-probe and connect a 'scope to one or two sensors.

[Black92GS]

41 minutes ago, Schurkey said:

It's good diagnostic procedure to verify the battery and cables/fuses/fusible links etc., early-on in the process.  We know the battery is not properly charged, perhaps actually defective.  It's worth a shot.  Besides...corrosion in the battery cables can be hidden under the insulation, or behind the "sealed" side-terminal cable ends.

A 'scope is a useful tool, but in this case I'd be connecting a decent scan tool with graphing capability.  You'd get the same graphic representation of the various sensor signals as with a 'scope, but better in that you know the computer is actually receiving what the sensors are sending.  And you could verify EVERY sensor with a scan tool in the time it takes to back-probe and connect a 'scope to one or two sensors.

I definitely agree.  While 12.2 volts at the battery is on the lower side, it’s not what I would consider low enough to be suspect in this particular situation, especially if the voltage at the battery is 14 when running. Since there is no separate TCM, and everything is run within the PCM, I would expect power and ground issues there to manifest themselves in other, possibly more obvious ways first. This is just based on my personal experience with these cars over the years  

And yes, a scan tool that can graph the sensors is a valuable check as well. The thing that will catch you is when you find the VSS data the PCM is receiving to be faulty…what is the cause?  The VSS has already been replaced with no improvement. Coupled with the trans shifting weird right when the speedometer fluctuates…I’m all but certain that scan data will mirror the speedometer. If you were able to scope the output at the VSS and it’s clean while the scan tool data is faulty, you have a better idea where to look next. If the data at the VSS itself is faulty or the amplitude is weak, then you focus your efforts there.  
 

One other thing I forgot to mention before, double check the length of the new VSS against the original one you removed.  Verify that they are the same length.  If the new one happens to be a touch shorter…it could be generating a weaker signal than the PCM would like potentially be problematic.  

 

[skatey]

9 hours ago, Black92GS said:

If it seems to be affected by bumps, I wouldn't come close to condemning the PCM just yet. Checking the reluctor wheel should be as simple as pulling the VSS and reaching inside the hole with your finger.  You should be able to touch the reluctor just enough to be able to feel for any play.  It's supposed to be tight and should only want to move along with the rest of the diff. If it feels like you can move it around without much effort...then you have an idea of where to look next.  At least pulling the diff on 4t65e can be done by a single person, with the trans in the car using fairly basic tools.

If that checks out, you could re-install the VSS and try running the vehicle up in the air and seeing what happens.  If the speedometer reading seems fairly stable, you could carefully try playing around with the wire while it's running in the air to see if you can cause it to act up.

The reluctor is the silver toothed thing on the right side, and the hole for the VSS would be in the differential carrier directly above it.  

Now if the reluctor wheel is the issue how do I go about tightening that or is it something I just need to replace?

[skatey]

3 hours ago, Black92GS said:

I definitely agree.  While 12.2 volts at the battery is on the lower side, it’s not what I would consider low enough to be suspect in this particular situation, especially if the voltage at the battery is 14 when running. Since there is no separate TCM, and everything is run within the PCM, I would expect power and ground issues there to manifest themselves in other, possibly more obvious ways first. This is just based on my personal experience with these cars over the years  

And yes, a scan tool that can graph the sensors is a valuable check as well. The thing that will catch you is when you find the VSS data the PCM is receiving to be faulty…what is the cause?  The VSS has already been replaced with no improvement. Coupled with the trans shifting weird right when the speedometer fluctuates…I’m all but certain that scan data will mirror the speedometer. If you were able to scope the output at the VSS and it’s clean while the scan tool data is faulty, you have a better idea where to look next. If the data at the VSS itself is faulty or the amplitude is weak, then you focus your efforts there.  
 

One other thing I forgot to mention before, double check the length of the new VSS against the original one you removed.  Verify that they are the same length.  If the new one happens to be a touch shorter…it could be generating a weaker signal than the PCM would like potentially be problematic.  

 

The vss was a direct match and didn’t notice anything different in terms of the shape of them. Now when I’m not moving, the speedometer is fine no issues and when I start moving, usually around 20-35 mph it likes to start unless there’s a bump then it’ll start earlier on as far as I’ve noticed. I actually ended up finding out that I needed to check my tranny fluid with the car started and she was about 2 quarts low from a time where the trans cooler line fitting on the radiator broke and it was peeing out tranny fluid. But I would’ve thought a tranny issue would happen sooner if it being low was the issue or even start whining. While I’m doing what I can I’m new to electrical on cars and worried about messing some up but so far I’ve done all the work and nones gone wrong once i fixed it but this one is throwing me for a loop since I’ve been doing continuous research.

[Black92GS]

Just out of curiosity, what brand of VSS did you install, and what is the part number of it? You also said you changed the pigtail. I'm assuming the new VSS came with the pigtail as well, and you didn't have to buy it separately, correct?  It's not a uncommon occurrence to receive a defective new part right out of the box, especially when it comes to aftermarket electronic components of any type....so keep that in mind as well that the new part could simply be bad.

The pigtail is what I focused on though.  Rockauto lists a number of different VSS options for a 99 GP GTP.  Walker is the only option there that includes a pigtail...but they list 2 different sensors for a 99 GP GTP. One states is for the 4t60e (3100 powered cars only....which no GTP would have) and the other for the 4t65e. Each has their own part number. They both look virtually identical to each other in the pictures, and since the 4t65e is essentially an updated and beefed up version of the 4t60e....They likely are physically the same.  Electrically though, they are almost certainly different, hence the different part numbers.  It's possible that the electrical connectors are ever so slightly different between the 2 that they shouldn't plug into each other's connectors....but if the new sensor came with a new pigtail which was installed.....it's going to plug in.

Check all of that out first before you go any further.   Based on the pictures of all the sensors on rockauto, the 4t60e sensors have a small exposed metal circle on the end that sits inside the trans.  The ones that state they are for the 4t65e are solid plastic. 

[skatey]

18 hours ago, Black92GS said:

Just out of curiosity, what brand of VSS did you install, and what is the part number of it? You also said you changed the pigtail. I'm assuming the new VSS came with the pigtail as well, and you didn't have to buy it separately, correct?  It's not a uncommon occurrence to receive a defective new part right out of the box, especially when it comes to aftermarket electronic components of any type....so keep that in mind as well that the new part could simply be bad.

The pigtail is what I focused on though.  Rockauto lists a number of different VSS options for a 99 GP GTP.  Walker is the only option there that includes a pigtail...but they list 2 different sensors for a 99 GP GTP. One states is for the 4t60e (3100 powered cars only....which no GTP would have) and the other for the 4t65e. Each has their own part number. They both look virtually identical to each other in the pictures, and since the 4t65e is essentially an updated and beefed up version of the 4t60e....They likely are physically the same.  Electrically though, they are almost certainly different, hence the different part numbers.  It's possible that the electrical connectors are ever so slightly different between the 2 that they shouldn't plug into each other's connectors....but if the new sensor came with a new pigtail which was installed.....it's going to plug in.

Check all of that out first before you go any further.   Based on the pictures of all the sensors on rockauto, the 4t60e sensors have a small exposed metal circle on the end that sits inside the trans.  The ones that state they are for the 4t65e are solid plastic. 

I got the sensor at AutoZone and the pigtail at o Riley’s because I was forced on getting the car fixed since it’s my way of transportation and work two jobs. Now ik the pigtail isn’t bad because it’s still reading the speed, but a defective vss could be a problem as you mentioned 

[skatey]

12 hours ago, skatey said:

I got the sensor at AutoZone and the pigtail at o Riley’s because I was forced on getting the car fixed since it’s my way of transportation and work two jobs. Now ik the pigtail isn’t bad because it’s still reading the speed, but a defective vss could be a problem as you mentioned 

UPDATE: I unplugged the speed sensor and while ofc there’s no speed on the speedometer it’s not throwing me a check engine light. So now could that be a sign of a break maybe in the wiring farther up the harness or something with the pcm?

[skatey]

Do you guys know how many ohms the vss pigtail should be reading with the car on the on position but no running, I checked it  and got about 28 and some change

[Black92GS]

3 hours ago, skatey said:

Do you guys know how many ohms the vss pigtail should be reading with the car on the on position but no running, I checked it  and got about 28 and some change

That doesn’t sound right. I don’t know the value off the top of my head, but the speed sensor itself appears to be in the 1000 ohm neighbourhood. The empty circuit would need to be much higher than that to function properly. 28 ohms on the circuit without the sensor connected could also explain the lack of circuit codes when the sensor unplugged, since the typical high resistance in the circuit that would indicate an open isn’t there. It may also be just high enough to not set a circuit low code either to indicate a short. 
 

The sensor should feed into the PCM directly. I would carefully unplug the connectors at the PCM and measure the resistance at the sensor connector again. You should have a completely open circuit. If not, the issue is in the wiring or the connectors between the PCM and the sensor, and you would need to find the corrosion or the short.

If you do have an open circuit with the PCM disconnected, check for any signs of corrosion on the pins of the PCM. If it looks good, reconnect and check again. If resistance is still in a similar range at the connector, try tapping on the PCM while you watch the resistance to see if jumps around. If it does…then the issue is within the PCM. 

[skatey]

I still have the issue going on, after taking it to aamco, they said they tightened the battery terminal bolts and it was fixed, well that was true for a couple days. So now it’s doing it again but not as bad. The last couple days tho my car had stalled a couple times while driving and I read that the sensor reading wrong could cause it to. Kind of stuck on this and the last thing I can think of is to solder those wires on the pigtail together inside of using a butt connector. Besides that I’m thinking I’m going to need a new harness or get it rebuilt. Last thing I wanna do is have to pull a transmission from a junkyard or some even tho it would only be a couple 100 bucks, just don’t have all that time right now.

[Black92GS]

I’m still convinced there is something up with the wiring itself between the VSS and the PCM. If tightening the negative seemed to help…take a look to see what else might have been touched in the vicinity.  Go as far as to follow the battery cables and see what other wiring could be disturbed by the battery cables being moved around. 
 

They likely found the negative connection to be loose by moving it. I don’t think that was the issue itself, but the battery cables being moved around a bit might have touched or moved another wiring harness just enough to temporarily fix your issue.