When I bought my 2.5L ‘87 Fiero with the 5-Speed two years ago, I didn't know anything about trouble codes or "Service Engine Soon" lights. I know a bit more now. :(

When I bought the car, I didn't realize that the b*st*rd I had bought the car from had disconnected the Service Engine Soon light. He had obviously done that so that I wouldn't notice that there were problems.

One of the trouble codes that had been stored was Code 24 - Vehicle Speed Sensor. Apparently, among other things, it is the information from this sensor that "controls" the electronic speedometer in the Fiero. I've never had any problem with the speedometer, yet I cannot keep this code from reappearing as soon as I move the car after resetting the codes. What does this indicate?

I'd like to be able to replace the Service Engine Soon light, but I've left it out because I got tired of seeing that red light on all the time. The disadvantage of simply leaving it out all the time, is that if something else goes wrong, I don't have that visual indication.

Any suggestions on this code 24 problem?

either the VSS is feeding crudy signal, or the ECM is getting a cruddy signal. Pull the VSS and clean it up. might have a flaky contact on it.

Assuming the VSS & speedo realy are working & acurate, I'd next look at the wire harness really careful. a lose wire feeding the ECM could be a problem. The ECM itself could have a problem. There's not very much connected to the VSS. Make sure you check all engine grounds.

Thanks for the tips, Ogre. I'm just looking over a wiring diagram in my Haynes manual, and it appears like the wiring (YEL & PPL) possibly goes directly from the VSS to the instrument panel. But in the trouble code section it advises to check the connection at the ECM when investigating a code 24. This is very confusing.

Wherever the wiring from the VSS eventually does go, would a continuity test on this wiring with a multimeter be the appropriate thing to do? (After disconnecting the battery?)

Sorry to direct all this stuff at you Ogre, but no one else seems able or prepared to step up and tackle these technical questions.

continuity probably won't tell you much, and done wrong could damage the ECM.

Try pulling apart, and reseating all the connectors to the ECM. any other connectors along the line that look messy. the VSS is a low voltage output, like 1-2 vac, at very low current if i'm reading it right. any corosion could interfere with it.

Cliff,,,, you guys build the dash, what voltage is the VSS output?

To be honest, I'm not sure. We don't use the VSS output directly...

But, if your speedometer is working, than your VSS should be working fine. What might be the culprit is the dashboard itself. The ECM is not fed directly by the VSS. The VSS pulses are cleaned up and divided by two by the dashboard, and this is the signal that is fed into the ECM.

in that case..... you can also pull the dash connectors and reseat them.

that would explian some of the info i'm looking at about how the ECM works.... I thought the thing I was reading had a typo.... it said the ECM uses 2K pulses per mile. didn't make sence when I knew the VSS is twice that.

Well, I'm glad I could finally help you with clearing something up!!! ;)

Heyyyyyy, we got Cliff involved! Waytago Ogre!

You may have something there, Cliff. Now that I'm studying my wiring diagram again, I can see that there is a BRN wire (carrying 2000 pulses per mile) that goes from the instrument panel to the ECM. Shortly after I bought the car, I had the entire dash, instrument panel, out and apart, so all those connections there have already been "reseated", but now I'll concentrate on the BRN wire and it's connection at the ECM. I don't know what, if anything, could go wrong with the device that cuts the pulses in half within the instrument panel. Assuming (dangerous thing to do) that there is nothing wrong with it, I'll deal with the wiring from that point on first. Thanks Cliff.

Ogre, I just wanted to clarify my "continuity" check inquiry. In order to make sure that there was no break in a wire anywhere along it's path, would not disconnecting it at each end and doing a continuity check at least tell me if there was a problem with it or not? Keep in mind that any wiring I would be checking would not still be connected to the ECM or to any source of power.

that might work, you want to use a good meter. you want to see if there's even a few ohm on the wire.

that's kind of a short line to the ECM, and its all inside the car, so it should be ok as long as it didn't get pinched some place. check it to ground as well as end to end.

if the wire is ok, it probably is, you could have a problem with either the ECM, or the dash output. If you have access to an ocyloscope, you can look at the feed from the dash to make sure it's consitant. if it is then the ECM may be failing. could be anything, a bad ECM, a cracked trace or solder joint in the ECM or dash..... You had the dash out, its posible you cracked something and it didn't show up right away.

Well, anything's possible, but I don't think I cracked anything when I had the dash out. Keep in mind that there was this code 24 problem right from the start. Shortly after I bought the car and realized that the Service Engine Soon light bulb had been removed, I installed a bulb and then accessed the codes. A code 24 (among others) had been stored long before I removed the dash.

I much prefer fixing mechanical problems. This electrical stuff is much too finicky. :)

duh,,,, ogre have short memory.... i read that alredy.....

if it's not the wire, it's either the ECM or the dash. If the dash looked good when you had it out, then try the ECM. Remember tho, the dash has been out at least twice now that you know about. There just isn't anything else connected in that circuit to look at.

If it's a cracked solder joint in either one, you may not be able to see it without ripping things apart, and getting a big magnifier. (looking for solder cracks with a hand lens is reeeeealy tedious.)