Insturment Cluster/PCM Problem? Please help

goldsun767 · 08-24-2007, 01:03 AM

I have a 97 grand prix v6 3.8 no super charger. I started to have some issues with my dash cluster Speedometer, trip reader, odometer, and cruise stopped working. Rpm gauge still works as well as the heads up display except for the MPH it stays at 0 but all the other features work on it. So I took it to a cluster shop in town and they said it was the cluster so I replaced it and had the same problems. I took it back to the shop and they started testing all the wires. His conclusion was most likely the PCM. He can get readings of speed from the VSS but not out of the PCM here’s what he wrote on a sheet for me.
Scan tool indicates a VSS signal
Speedometer, trip reading, odometer, cruise not working
VSS signal to PCM good
VSS output at PCM pin 13 dk. Green no signal to cruise or speedometer
My question here is the GM dealers in town say if we got a new PCM it would be like $400 plus $150 to install plus they have to check the car out them self’s at $100 a hour. But the local junk yard has used ones for $40 and I am looking at doing that. One dealer says they won’t touch a used part must be new the other says they will but we are responsible if anything happens to the car from the part if it does not work. My problem is both dealers said a replacement PCM has to be programmed but I talked to Midas and they said they have done them and never reprogrammed them I don’t know if they are thinking new or used but they said never have to program them. Next one of the dealers said sometimes the PCM can only be programmed once. I have a Hanes repair manual and it says it can be reprogrammed but has to be done at the dealer. Next the junk yard said as long as the 8 digit code matches on their part with the one that’s on the one in the car it may not need to be programmed. I guess I am wondering what I should do I don’t have the money for a new one I would like to try the used one but if it’s wrong I was told it can lock a car. Wondering if anyone has ever replaced one or has any other ideas we would like to try to fix this by Thursday as we are going out of town with this car. Also any help for location or taking the PCM out would be great.

BNaylor · 08-25-2007, 07:41 AM

Well from what you are saying it sounds like some good troubleshooting was performed with a proper scanner so the PCM module sounds suspect other than output wiring to the IP Cluster. The rule of thumb is a new PCM module has to be programmed or flashed. A used one as long as it matches your id label of the PCM and specific year, model should work. Sometimes used or pull is the best route to save money. However, regardless of whether it is new or used the VIN and other pertinent info will need to be programmed in. Reason is so that when a GM Tech II scanner is used it will operate properly and pull up the right menus/tables. Also, a crank variation learn may have to be performed but should not preclude proper operation. The PCM module is located in the airbox assembly and very easy to replace.

goldsun767 · 08-25-2007, 03:06 PM

so do you think the used pcm as long as it is the same model will wwork at all with out reprogramming it. We plan to get the used one and the car is going to be drove into the ground. So if it will work and read speed then I may not flash it. Otherwise I plan on getting the used one and taking it to the dealer to install and flash it. let me know what you think

BNaylor · 08-25-2007, 09:57 PM

There are no guarantees you won't have any problems but it should work and for troubleshooting purposes to see if you get the proper VSS signal processing. I've tested one from a salvage/pull in my GTP and it worked fine. However, it was later sent in to get re-programmed by Intense but that is a different matter altogether.

GrandPrixLady · 09-15-2007, 02:01 PM

I had a similar problem on my 2000 GT. I had problems with the fuel gauge at first, then the trip computer and trac control. On a 2000, there is a serial data bus that sends data to the cluster, traction control and trip computer. I found a TSB (techinical service bulletin) that pertains to the wiring harness. The harness is routed past the a/c accumualtor and it rubs against the mouting flange. I would check the harness for broken wires. Mine had 5 wires that had been worn through. Everything now works fine. Hope this is helpful.

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