Hello i went on a 1-2 hour cruise last night with cruise control across town on my way back i noticed it bucking so i braked to kill off cruise control and had stopped at a gas station to check under my car to make sure i had no fluid leaks after doing maintenance to it a few months ago. Directly after i noticed my speedometer wasnt working but was peaking up 2-3-10 mph when in 2nd maybe 30 mph and the car wouldnt shift so i was able to make it home. Overnight i disconnected the battery and took it around the block today now the speedometer is working and its shifting but i noticed its real slow to go up in mph as well as decel in mph vs what the cars actual speed is. The speedometer has a real slow response or delayed in catching up in terms of mph vs what the car is actually doing. Once at 50-60mph it stays hanging up there or banging around while im braking down towards 30 mph. Anyone have this problem? Only thing i can of is the vehicle speed sensor or some magnetic interference. Does anyone have a picture of what the vss prongs/spade terminals should look like so i can confirm my speed sensor harness plug isn't opened up too much and is making contact just fine. I had only unplugged it 2-3 times and was working great before running into this issue. Should i spray some qr electric cleaner? I do have a battery that goes dead in a week if i dont start the car every few days but is more of a daily driver vehicle if you ask me. Tomorrow ill have the funds for a new walmart battery VP-78 which it calls for.

 

Heres what it does. Speedometer has a slow resposne or when driving it takes a while for the speedometer to catch up and does jump around 5-10mph once at a speed. I believe it operates like an electromagnetic pulse. Ill buy a battery and if its still doing it maybe a speed sensor. Anyone know where the vss wires are linked to up at the front or easy way to access them to make sure there's no damage to them and a continuity test? When braking the speedometer has a slow response as well for the needle to drop and bounce around so maybe its the speed sensor if its possible to have one that acts like this?

 

I would get a cheap Bluetooth adapter and using an app like torque on your cell phone read the vehicle speed. If it's stable it's probably the speedometer stepper motor going bad. What's it do when you switch to km

 

I'll try km tomorrow after swapping out new batteries. So you're saying it would need a new gauge cluster? Yes I should be able to download a speed app but it does indeed need the speedometer for it to shift correctly as it's an automatic 99. Will any 97-04 gauge cluster work, a z06 has the left side HUD? controls I believe will one of those work or can you replace just that part of the speedometer or repair? Also anything wrong with the standard 600CCA batteries or should I try to get an 800CCA. I think the 600CCA should be fine.

 

Any sensors in the car that are AC driven...Knock Sensors, VSS (speedometer), Wheel Speed Sensors (your bucking possibly ??) can whig out if unwanted AC from a bad or failing alternator diode creeps into the electrical system...if you have had a parasitic battery drain this could be a symptom...simple test is with a multimeter....positive lead to alternator B+ and negative lead to ground...run the car at 2000 RPM with some loads on it and see what you have. Not saying this is your problem but something that can be quickly looked at if you have some issues with one of these sensors...0.1 to 0.2 volts AC is OK !!...why are you changing your battery ??????????

 

I think the OP has a battery that dies in a week, based on this quoted part from post 1:

 

Well if it is a parasitic drain a failing or failed diode in the alternator should be addressed !!

 

I don't believe there's a battery drain but is an older battery 1 year 7 months old. I found out the battery was old after having the car down for 3 weeks with cables disconnected when adding headers and doing some other maintenance that the battery was dead when I went back to start the vehicle. After jump starting I figured out it takes about a week for the battery to go dead on it's own if you don't start the car twice a week. I usually use the auto mobile daily driven or take it out a few times a week. Today I have the funds I'm going to purchase a new battery. The cars never gave me " high or low voltage" that would come from a bad alternator and reads 13.4 usually sometimes higher it stays about the same as it has the decoupler pulley or regulator somewhere. I do have led tail lights and projector or the cheaper 250$ was the cheapest I believe headlights but seen they use a regular bulb. The led tail lights and turn signals hyper flash or blink twice as fast when on. Only thing I noticed was after putting the car back together after rebuilding torque tube was it throws a c1761 sometimes and another code for both front shock sensors and service RTD. I believe I read they'd throw this code with LED and no resistor for hyperflash.

 

Your vss is in the top of the differential.

 

Yes, I checked it with a 6" harness connector a couple weeks ago and tested 1480 on the ohm meter. I read that 1300-1800 was the correct ohm resistance for vss. Anyone know where to two wires from the same speed sensor go to inside the cabin and/or engine bay of the vehicle? That way i can check it for a continuity test for no damaged wires?

 

Your battery should NOT be going dead after a week !!…you should get about a month based on a 30 mA drain on a fully charged battery…if you have a drain and your new battery goes dead a few times it’s service life is shorted immensely but you can do what you want…you should also buy a battery with a 120 or 140 RC.

 

i changed my diff out and have a similar issue. speedo only goes to like 10mph until i hit about 50mph and it jumps to correct speed. i have a feeling I squished a wire somewhere while reinstalling the real subframe. id like to know where those vss wires go to check continuity/shorts also

 

Not saying you need a new cluster. You have to troubleshoot it to isolate the failure first. An easy way is to use a cheap obd2 scanner J1850 compatible and your phone to see what the digital speed reading is doing. If you had a hand held scanner you can also get the same information from there. As per C5 diag suggestion If you have a digital voltmeter you can set it to the AC mvolt scale and see what the AC ripple is at the battery After you have this information you may have a clue as to what's happening.

 

Ok just purchased a new vp-78 battery from walmart and the previous owner had a vp-75 550cca that was 1.5 years old but didnt have any problems with it just being an old weak battery. Directly after swapping it in my car gets the pull key wait 10 seconds. Tried 2 or 3 different key cycles and still does the same thing. I noticed the car dies right away with the speedometer at 0 as it did a few months ago with the speedometer working. After having that issue 4 months ago i put the lcm5 module and didn't have issues with it until today. I also cut the brown loop as instructed as it did do the pull key wait 10 seconds but that was months ago. So now what could the issue be? So apparently with the speedometer at 0 or having its lag the VSS is reading 2 mph as it dies instantly after letting off the brake. The speedometer does go up the few mph but after the cars already died from the 2 mph cut off from pull key wait ten seconds. So what could the issue be here? It would appear the vss is working but speedometer is slow to respond. This is interesting to say the least. So i guess ill wait a while before starting the car again. What do i do if i get the pull key wait 10 seconds and the car keeps dieing with the lcm5 module installed from a previous thread which had solved that issue? Car is a 99 auto do you just leave the battery disconnected overnight for the pcm to reset?

 

Ok new battery in i checked every fuse with a power probe without supplying power most read 14.3 volts some 13.7 i guess under a load with the vehicle idoling and they all checked out good. Didn't have the "pull key wait 10 seconds" 10 minutes after checking the fuses i took it for a test drive it seems to have cleared the SES light due to the battery swap for rear o2s deleted so will probably take a few key cycles. Sometimes the speedometer gets hung low making it shift od/d which seems to be a big problem as the auto uses the speedometer for shifting as we learned in a previous thread. Heres what its doing with the new battery which tests good I believe with the alternator testing good as well so still a speedometer issue.

 

Thanks any help on this is greatly appreciated. I can maybe jack it up and spin the wheels in neutral should maybe read higher in ohms with a 6" pigtail connector i have and an ohm meter.

 

The PCM controls the transmission shifting from the VSS not the speedometer. The PCM sends the vehicle speed to the speedometer. You said that the transmission is not shifting properly so it's most likely a VSS circuit problem, wiring or the Speed sensor itself. The VSS sensor is pretty cheap so you could replace it, about $20 on Amazon. If you don't want to do that you can check all of the wiring and maybe look at the VSS output with a graphing Multimeter or a scope.

 

I've confirmed that if the speedometer mph isnt within range of engine rpm the shifts will act up. So i've found an ac delco VSS for 32$ on amazon. Certain electronics or sensors i would get name brand i've had a new ebay map sensor that was junk on a turbo car. Anyone have a spare vss sensor they can test or know the ohm resistance of one? Mine tested 1480 on the ohm meter unplugged from the harness but with that being said is it possible that it be faulty once generating AC or current? I'll give it a few days and if its not corrected ill probably fork over the 32$ for a new one but does anyone know where the 2 VSS wires go to inside the cabin fuse box or engine bar or directly to the cluster? One schematic showed them going straight to the Instrument panel i had seen in another thread. The transmission shifts great when the speedometer is working the only issues i have is it shifting funny while this speedo bounces around with slow response up and down in mph. May i ask if the speed sensor contains a magnet? Any way metal could be stuck on it causing this issue.

 

It is a magnetic pickup. Not sure how the wires are routed from the VSS, but it goes directly to the PCM. It won't hurt anything to remove the sensor and look at it. You can check that the wires are not shorted or open at the VSS connector.

 

I don't think there's a wire problem unless there's a problem right at the plug on the harness. I did have it unplugged and hanging for 2 months in the driveway while rebuilding the torque tube. I did trouble shoot this a few weeks ago when the speedometer was reading 0 the whole time. How would you got about testing the wires on the harness with an ohm meter? I may spray some electric cleaner on the plug but looked pretty clean to me. How would you check to see if the wires werent shorted or disconnected at the sensor? Only way i can think of is find them in the cabin and a continuity test from the plug to where they lead in cabin and or engine bay.