GEN IV, No Gages, Electrical Fault, No Serial data

Hi to all Gen IV Oldsmobile Toronado owners with the dreaded gage failure problem on the Instrument Panel Cluster (IPC). In my car I have the color Visual Information Center (VIC), though that does not materially alter the diagnosis/repair.

You have this problem if, when you start the car you have no speedo, no gages, a/con packed up, outside temp is -40 and probably the heated rear windshield is on. The Taco works however. This applies to the analog gage cluster, I don't know about the digital one, (but experience indicates now that it does NOT apply, the central power supply is being listed by some as causing a similar problem with their digital IPCs. Also my 1991 car does not have a central power supply, so this must be 1990 and earlier. I do know that a 1990 _Analog_ IPC will work in a 1991 car.)

(Concerning the digital cluster on a 1988 Toro, this came from an e-mail on the Toro list, thanks to Ray : "The fix on Jonathan's site is for 90 model and newer Toros. It will not work on your car. I have an 88 also, and had a completely dead IPC. I tried it, the IPCs are different. I did find some things that might help you. You can send the part to www.directpart.com I believe they charge $180.00 plus shipping to repair your IPC. You can go to www.car-part.com and do a part search and buy a used one, which is what I did. I paid $100.00 for mine.") (The analog display has needle type gages that rotate (point). The digital display has bar type displays that light up segments and numeric readouts say of of mph).

Back to the analog display.

Some time during the day the problem fixes itself.

If you check codes, you have a whole bunch of 33x codes and E047 maybe. (You can only check for codes when the fault is not present.)

The serial data highway (circuit 800) is corrupt.

The IPC is causing a ground to the highway from the transmit Field Effect Transistor (FET) it uses to signal messages out on the highway. The "receive" function of the instrument panel cluster is working fine (though the IPC is in a "reset" state).

The fault is now determined, the necessary "reset" pulse simply fails to happen. It is an internal (to IPC) signal that somehow makes the whole thing come alive. Once the pulse arrives, the board comes on 1 second or so later. The pulse can take up to 2 hours to arrive! The reason the pulse does not happen is because a capacitor has failed and needs to be replaced.

You need to dismantle the Instrument Panel Cluster and replace the failed capacitor, not for the faint hearted. You also need to review all the comments and advice on this page before you begin.

I made some mistakes in my diagnosis that came to the attention of the manufacturer of the IPC. I have included the relevant e-mail at the end of these notes (with permission). Please read and take account of the points raised, my thanks to Mark for taking the trouble to write me.

To get at the IPC you need to remove the trim. I won't explain how except when you remove the bolster above the driver's knees (Gen IV Toronado, one long 7mm bolt from underneath) you _must_ pull horizontally backwards, or you will break the clips on the top face of it (either side of the steering wheel). I find removing the trim surrounding the IPC and VIC tricky too, it simply pulls away horizontally at the right hand end though.

Once you have the IPC out, you need to remove a large quantity of pozi-drive screws. Note how they all come out. You don't need to remove the aluminum heat-sink, but you do need to remove the 4 smaller screws in the middle of it. You need to remove both screws that hold the terminal block in. Make sure you use the exact right size screwdriver or you will damage the heads and on the ones that hold the terminal block in, this is bad news.

You can lift the gages slightly away from the main board (the IPC splits in half). There are three ribbon cables. Two are disconnected from the board by pulling gently straight up on the blue connector block. (Left & Right). The middle one is removed from the gage side by releasing the catch. This is a white bezel that goes right round the cable. Pull it away from the gages' plug by about 2mm, it acts like a sort of wedge. Once it has moved back by 2mm, the ribbon cable will pull out very easily. If you have not seen this done talk to somebody who works on laptops, these connectors are very common in them. (They are used inside CD players too...!)

Now you can separate the two halves. The main board is secured by 4-5 pozi-drive screws similar to the ones you have already removed (there is an insulating sheet as well, note which screws hold it in and which are under it). There are two different looking pozi-drive screws that hold the internal heat-sink in place (same appearance as the 4 on the outside you have already removed), leave those alone. The board will come out very easily when it is loose, but you might need to use slight pressure to get it started. The board is pressed over some plastic mounting pins about 2mm high, so after 2mm of movement it comes completely free. There are two sets of lamps hanging off either end of the board. Don't break their ribbon cables, just live with them getting in the way all the time. Take precautions to inhibit static damage (see below for link). Replace the capacitor described below.

Putting it back is much the opposite of taking it apart, but when reconnecting that center ribbon cable make sure it is _fully_ seated before pushing the bezel back into place. I find the bezel has always managed to go back into "lock" position, so I have to unlock it first. There is not much room and you need to make sure that the bright connector pads are completely inside the connector block. It must also be "square" in the plug. Also be certain that you connect the ribbon cable blocks onto the right posts in the connector, it is easy to miss by one.

I have had problems getting the two screws that hold the terminal block in place back in. I have found that the block holds itself out of alignment and you need to push on it firmly to make the holes line up (the block will move relative to the board on two flexible ribbon cables). You'll see what I mean when you come to do this. If you don't you will strip the brass threaded nuts (as I know only too well <g>). Those bolts travel easily when straight. You _must_ check that the terminal block is firm in the IPC's housing. When the bolts are firm, try to move the terminal block. If it moves you have cross threaded the screws and they have jammed with the block not in place. You _must_ remedy this as the connector holds on the slimmest possible margin electrically speaking.

With the IPC main board out, hold the board with the heat-sinks to the bottom left and the components on the upper side (toward you).

Look to the left of the board and you will find an electrolytic capacitor (one of several) rated at 3.3microFarads, 50v. It is just above a 100microFarad 63v almost touching it. To the left and down slightly is a 220microFarad 10v and slightly right and further up the board is an inductor (white thing looks a bit like a plastic thumb tack). To the right of the inductor are two more 100microFarad capacitors and to the right of those and down a bit is one more 100microFarad capacitor. Going back to the heat-sink, on the very left of it there is a 220microFarad capacitor 25v.

The problem is the 3.3microFarad capacitor. It is tiny and the terminals are _very_ close together. It is also mounted very tight to the board. Crud has built up under the capacitor between the terminals causing a short at about 3000ohms (for me anyway). The capacitor fails to charge up (especially in damp weather...!, conducts through the crud I guess) and so the voltage to the chip immediately to it's right (I assume a Toshiba reset chip) never sees the "time to reset" voltage. The "crud" is the contents of the capacitor leaking out. Anyways, replace it.

And then you are done I hope.

Oh, you don't need to disconnect the battery but you MUST NOT have the ignition on. Well, I never have removed the battery.

As ever any advice is offered on a "use at own risk" basis, if you blow up your IPC don't talk to me, this advice is offered without any warranty express or implied.

Key words:

Gauge failure, Gage failure, No Speedo, No Speedometer, Heated rear windshield on, Circuit 800 serial data highway failure, Circuit 555 Wakeup failure, Circuit 555 wake-up failure, Instrument Panel Cluster failure, IPC failure, General Motors, Oldsmobile, Gen IV, 8192, P4, ECM, BCM, PCM.

Aug/30/2000