silver twin

I have just purchased a 2001 Z06 and the speedo quit working where should I begin in trying to figure this out,or should I just replace the cluster or get it repaired.
Thanks
Phil

dadaroo

Let's do some diagnostics before we decide to start replacing parts. Do this for me, can you set the cruise control and have it work and display the speed setting on the DIC? That can maybe tell us if the Vehicle Speed Sensor (VSS) is working and getting a signal to the dash thru the PCM. The PCM feeds the speedo and the DIC via 2 different ways. My guess is that it is working since you don't apparently show an issue with active handling which the VSS feeds also thru the PCM.

Also pull up any codes you have and post the results for us.

In addition, do you have HUD? If so does it indicate MPH?

silver twin

Dadaroo
Thank you for your quick response,but I am not sure what the Dic is are you saying for me to set the cruice and see if it registers on the speedo.Maybe this is a shop issue for me.The car does not have HUD.
Phil

lionelhutz

Go driving down the road and set the cruise. The car will show the cruise setting in the DIC (driver information center, the display under the gauges) if the cruise is working. The DIC is fed via the serial bus and the speedo is fed via a dedicated signal from the PCM so this test will help narrow down the problem.

If the cruise doesn't work then it could be the vehicle speed sensor, the wiring from the VSS to the PCM or the PCM.

If the cruise does work then it could be the speed output from the PCM to the cluster or it could be the wiring between the PCM and the cluster or it could be the cluster itself.

I would also pull the battery and look at the tray below. The PCM and a bunch of wiring is below the battery and if the battery leaks it gets acid all over the PCM and wiring.

silver twin

Took the car for a quick ride and the criuse does work and it registered the speed on the DIC for about 10 sec,so from what you said it will either be the speed output from the PCM to the cluster or the wiring or the cluster correct.
Phil

lionelhutz

Yup, it's one of those 3.

silver twin

Thanks for your help.
Phil

dadaroo

Thanks for your help Lionelhutz. Phil, we worked on a similar issue recently at this post (http://forums.corvetteforum.com/c5-t...ering-mph.html). It was a bad PCM but he was getting a suspension code also. If you look at the attached 2001 schematic you will see the VSS signal output at PCM Connector C2 goes into Splice 204 which feeds the IPC and the suspension module. Since you are only having a problem with the speedo the problem would appear to be somewhere from the splice to the IPC. Most likely a connector or the actual guage. With that being said, many things have been fixed by just disconnectiong the battery for a few minutes and then reconnecting. At least it is easy and free.

So everyone knows, Phil gave me 2 codes from the DIC:

P0410HC PCM code related to the secondary air pump. I suggest we dismiss this issue as being a related problem. Would be better to chase in another thread.

P0608HC PCM related code to the IPC which is our issue at hand.

At this point I can't think of anything else to do. Maybe someone else has some additional ideas or some magic dust. Hope you don't have to pull the IPC. I will stick with you until you get it resolved.

SPEED750

When you turn the key on, does the speedo do a full sweep of the gauge? If it never moves it could be the little motor that moves the needle.

lionelhutz

One thing to note is that you have a Z06 and it won't have the ESC module.

P0608 indicates that the PCM has measured the VSS output signal and that it doesn't match what the PCM was commanding.

This is basically how the circuit works.
The IPC has a resistor connected between +12V and the VSS wire.
The PCM has a transistor switch connected between the VSS wire and ground.
The PCM turns the switch on and off.
When the switch is off, the wire will measure around +12V.
When the switch is on, the wire will measure around ground or 0V.

The PCM will measure the voltage on the output pin. If the voltage isn't 12V with the switch off or 0V with the switch on then it will set the code.

The first step I would do is measure the voltage on the wire at the PCM or one of the connectors between the IPC and PCM (C102 or C150). You're looking to see if the wire to the PCM has 12V on it with the key on.

I think if you wanted to do a crude speedo test you could connect a jumper wire to the VSS wire at one of the connectors and then keep rapidly touching it to ground and see if the speedo reads. If it's like the older GM stuff (which it likely is), 2000 touches per minute would be 60mph, so it shouldn't be that hard to "morse code" the wire to get a reading.

The bad condition to set P0608 has to persist for 5 minutes while >400rpm so I suspect the PCM is not seeing the 12V from the IPC due to a broken wire. The code will likely set again if you just start the car and let it idle for about 5 minutes.

silver twin

Lionelhutz
If there is a suspension code,what will it show up as on the DIC.
Phil

lionelhutz

It would but if you don't have the ride control shock switch on the console you don't even have the module that would give a code. My understanding is that Z06's never came with the F45 or F55 ride control option.

silver twin

Lionelhutz
Cleared all the codes last night,went for a quick ride this morning so that I could recheck the codes as before I got a PO410-c PO608 hc and a BO-RFA-U1064-H which is new.
Phil

dadaroo

Lionelhutz is correct and your Z06 did not come with the ESM module from the factory. I I got confused and thought it provided active handling which uses VSS input. However, that is done with the EBCM. Thanks for correcting my mistake. I am attaching the PCM connector (red one) showing pin 50 has the VSS signal to the IPC.

BTW: I would really like to know if you speedo does the full sweep at startup. That is important info.



Also here is the connector for the IPC in case you need it:

silver twin

The speedo and the odometor have no movement.
Thanks everyone for your help.
Phil

lionelhutz

The other gauges in the cluster work?

Just to clarify, the speedo never moves when you turn the key on.

I could see the odometer not acculating any mileage. It would make sense that the speed signal driving the speedo would also be used for the odometer.

silver twin

All other guages work just no speedo and no movement.
Phil

dadaroo

Lionelhutz, do you know where the start up speedo full sweep signal comes from? If you remember our friend in the UK would get a full sweep at startup but no normal MPH reading in the IPC or HUD. In addition his ESC module was throwing a RTD code. However his cruise worked and showed MPH in the DIC since these are serial bus signals on a different circuit. Ended up it was his PCM. If the same normal MPH circuit in the PCM sends the false signal at startup, then he should not have gotten the full sweep.

Knowing the false signal source could help determine the next step in diagnostics. My 2001 FSM only says at startup the MPH gauge is illuminated. Does not even say it does a sweep.

lionelhutz

I'm pretty sure the cluster or gauges will do the sweep internally.

The gauge not sweeping doesn't explain why the PCM thinks it's not outputting the correct speed signal. The circuit signal on a gauge with a stuck or damaged stepper motor would still most likely work and the PCM wouldn't know that the output signal was getting to the gauge cluster but not moving the needle.

Possibly the speedo part of the cluster has lost power due to an internal broken connection or the speedo circuit has completely fried so the input circuit is dead too.

silver twin

I was able to take to car to my friends body shop today and put the car on a hand held and drive it the hand held read the speed so from what my friend says its the speedo thats bad,whats your thoughts.
Phil