salaamq

Before I start I would like to say hello to everyone at the LS1 Forum!

I recently bought my 2002 Camaro Z28 4AT - about 2 weeks ago. I just started experiencing an odd issue with it a few days ago.
It began with the speedo randomly dropping a few mph when I am driving. Earlier today I noticed when this happened, my cruise control would get shut off. Then it started dropping to 0 when I was coasting on occasion, but it would hop back up right when I get back on the gas, and go back to dropping down a few mph while I'm on the gas.
A few miles after this, I notice it starts, and is stuck in second gear. (limp mode? No lights on in dash) The speedo is fairly jittery.
From what I have read, speedo issues could be caused by the voltage regulator acting up. I have noticed on occasion that the volt meter will drop to around 13 for a few seconds and go back up to the normal position after that. The voltage drops do not seem to directly affect the speedo. However, the second gear issue and cruise control getting shut off has really made me look elsewhere.
I am now thinking it could be either the VSS or the wiring. Is there anything else that could be causing this? Wondering if anyone else has had this issue before and could point me toward potential causes. Thanks everyone

salaamq

Bump...
I changed the vss and I still have the same problem. Anyone know where to look next?
Also any tips on following the transmission harness from the vss? It looks to be routed above the transmission so I cannot really inspect it well.

mrvedit

I would hook up a scanner that can read MP/H from the PCM and see what it reads. This will help you isolate if it is before or after the PCM.

I don't have a Gen-4, but from what I read here, the trans wiring goes straight up, is clamped above the trans and then goes forward to join the main engine harness. It is very hard to inspect in a Gen-4, so start with a scanner.

salaamq

Well the other day it was acting up a lot. It threw a code p0503 which is vehicle speed sensor a intermittent/erratic/high. Not sure if that would narrow it down any. I soldered in a new wire from the pigtail to the pcm, and still the same problem. Unless its the pigtail itself or the few inches of wire that I soldered to, I am lost. Would the dealer be able to tell me where it is exactly if I took it to them? I got an appointment with them in case I need it.

salaamq

There have got to be more people on this forum who can help.

The dealer was unable to get it to act up, and neither was I when I drove it back home today. What exactly could this be??? I'm not sure if I should re wire the whole vss? Or swap out the pcm?

The one reason I would suspect the pcm is cause when it throws the p0503 vss code it also throws a p0122 throttle position sensor code.

mrvedit

I also hope other have ideas, but these electrical gremlins can be difficult to figure out in person, much less through a forum.

Before blaming the PCM, I would double check ground connections. Determine where the PCM grounds and run a 14+ gauge wire from that point to the engine block. And make sure the battery to engine block connection is good and solid.

salaamq

And now, since the dealership is long closed, the car decides to act up.

There is one other thing I noticed while driving it tonight. Sometimes the volt meter will dip to 13 volts for a second, then go right back up to the normal 14-ish. The dash lights dim a little when this happens. Could this somehow be related?

mrvedit

Yes. This is sounding more and more like a bad ground connection.

salaamq

Didn't know grounds would cause intermittent issues like that.

I will try to trace and test them later on. Looks like they are on pins 1 and 40 on each connector to the pcm.

Should I just check resistance, or run new grounds to test?

mrvedit

Figure out where those PCM grounds connect to the engine or chassis. If to the engine, make sure those connections are clean; if to the chassis, run an additional ground wire to the engine block or heads.

Since your volt meter is reading erratically, your ground problem might not be with the PCM, but with the dash area or with the chassis to engine.

If you check resistance, remember to disconnect the battery first.

I am not guaranteeing it is a ground problem; just saying what I would do. (I've done cars and electronics for 40+ years.) While my '81 Camaro is in excellent condition with no corrosion, I still run my own ground wires so that I never have to count on the chassis for ground.

salaamq

The volt dip is not erratic, but occasional. Just so happened to notice that the lights dimmed a little when this happened for a second yesterday.

When the voltage dips, the speedo doesn't go whack at the same moment. I still will have a look at the grounds though, cause the throttle position code that also came up could also be on the same ground. The GM tech also suggested checking grounds. Throttle position is on the same plug as vss on the harness (blue section), and between 1 and 40 just like the vss connections. (Guessing pins 2 - 39 use the same ground? being ground at pin 1).

The only other things that I would know to do after grounds is re-wire the vss completely and if that doesn't solve it, then replace the pcm. Hopefully it's grounds and I don't have to go that far.

I have taken some video of the speedo jumping around, and if that would help I could post it somewhere.

Thanks for all the help you have given

salaamq

Noticed today when I had the AC on the voltage drops. It was steady around 13 and a bit (I would say 13.7 based on gauge) vs it's normal 14 and a bit. A couple times when the engine was just idling at a stop, it would drop down below 13. I think this was when the ac compressor engaged, via its clutch.. My blinker would also slow down as would the blower fan. When I got on the gas again the voltage would come back up. So I'm really thinking ground issue or maybe back to a whacky voltage regulator/alternator.

Also the car has started to be affected over speed bumps. The speedo will jitter when I go over them now and then. The issue is getting worse as miles pass.

Just have to find the time now to work on it.

salaamq

Finally got this car fixed.
I ordered a new VSS pigtail, pcm wiring pins, and re-wired the whole sensor. Works just fine now.
The voltage gauge still dips but does not have any effect on the speedometer.

mrvedit

Thank you for the update. Glad to hear you got it fixed.
Perhaps the VSS pigtail got yanked and damaged in the past the copper wiring finally split. Sorry if my ground connection suggestions wasted your time.