Code 24 and Fuses Blown (Page 1/1)
Kenpachi DEC 19, 12:43 PM
Hey guys, picked an original 84 Fiero 2M4 with (presumably) 34k miles. The car obviously sat in a garage for many years because it is in immaculate condition. No issues other than the speakers blown, radio crackle, and driver side headlight motor not functioning. I did the usual fixes, pcv valve, fuel filter, rotor cap/button, spark plugs and plug wires and I replaced the terribly squeaky old belt with a new belt.

After these changes, I'm now encountering these random issues. Speedo just stopped working. CEL is coming on and upon checking its code, I'm getting a code 24. Vehicle Speed Sensor? Everything seemed fine before doing the tune-up. I understand that the speedo not working within itself can throw that code. Odometer still working. I disconnected the connector to the VSS and cleaned it with electronic cleaner and plugged it back in. Nothing.

The other weird thing that has me stumped is while test-driving, the radion stopped working. Checked fuses and the radio fuse was blown. All other fuses were fine. Replaced fuse and radio worked for a second and then fuse must have blown shortly afterward. Checked grounds and didnt find anything off. I'm no electrical genius though I am probably missing something.

I do think when disconnecting and reconnecting the battery, the ECM cannot set correct idle because speedo isnt working. I had read that you have to drive up to 35 mph to get the ECM to set correctly.

Any help or thoughts would be greatly appreciated. I've spent hours across forums trying to learn and figure out what's going on to no avail
theogre DEC 19, 02:01 PM
what fuse? look @ label on the box.

Yes, 24 is cause by "Dead" speedo board. The path = VSS, Speedo, ECM.

VSS is OK Because Odo, maybe Trip too, still counts.

All Fiero Speedo board have 3 functions...
1 drive the speedo meter itself
2 drive 2 stepper motors for odo and trip
3 divides speed "data" for cruise and ECM.

Plus 4. 84 speedo is also Cruise Logic even if car doesn't have the option. Cruise in most later Fiero in done w/ separate box under carpet. 87-88 L4 has that built into ECM.

So yes, ECM can't see Speed "data" from that board then won't reset IAC and other problems. Do Not adjust Idle Stop on the TBI thinking that will help.

84 board is wired different then later boards & won't work even if you don't have cruise so don't care later board don't have Cruise logic.
Not sure even mount in 84 dash.

Why "dead?"
Could be a crack solder joint "killing" 1 or more functions above. Bad capacitors etc can do same.

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Kenpachi JAN 01, 03:11 PM
Sorry for the delay, the holidays proved to be a bit more busy than I liked.

Tried lots of things and still stuck. I cannot for the life of me find out what is going on.

It is the 10amp battery fuse that keeps blowing. The 84 models apparently have different fuse locations. This is a fuse box with "CRANK" on the very bottom right as opposed to CTSY/LID

I have checked all bulbs or grounds that might cause this issue. Disconnected the lighter in case that was causing the fuse to blow. I pretty much replaced all fuses with new ones. Pulled the radio out that was getting intermittent power and checked those wires/taped them off. Cleaned and checked the front hood and rear trunk AJAR latches. Still blowing the 10 radio fuse.

I did at one point get the car to keep from blowing the fuse at idle but as soon as I got up to exactly 10mph on the speedo board, it pops. Did this multiple times. At least got some change.

BUT. Just tried again today (I've gone through maybe 8-10 fuses) and now it pops on start up. Just that fuse!

It's particularly frustrating because this is preventing me from driving an otherwise almost pristine Fiero with 34k miles. It can't set idle through speedo and therefore drives kind of erratic.
theogre JAN 01, 06:19 PM
Lighter is on Bat Fuse for later years

But is on 20a ctsy fuse for you.
Pulling the lighter often won't help because of crap in the socket is the problem.

Alldatadiy.com has right data to fix wiring problems for 84.

See https://web.archive.org/web...cast.net/~fierocave/ lighter, wiring section too.

may need short detector kit for cars & other tools like DC Amp Clamp later.
Example: amazon etc search on short detector tool
fierosound JAN 05, 12:53 PM

quote
Originally posted by Kenpachi:

BUT. Just tried again today (I've gone through maybe 8-10 fuses) and now it pops on start up. Just that fuse!

It's particularly frustrating because this is preventing me from driving an otherwise almost pristine Fiero with 34k miles. It can't set idle through speedo and therefore drives kind of erratic.



Sorry to hear that. Hang in there. Persistence is the key.
You may need another 84 cluster for the speedo.

The radio fuse also ties in with the cruise control which circuitry is in the speedo on the 84 models.
Disconnecting the stalk lever and other items one by one may help isolate problem component.
It sucks, but you'll need another package of fuses to isolate this.

Start by unplugging speedo harness C1 from cluster.
It goes in the bottom left after you've removed the bottom trim panel.
If radio fuse doesn't blow and radio works, speedo is definitely the problem.

Get the 84 wiring diagrams here.
https://fieroinfo.com/

This is rear view of cluster showing all 3 harness connectors.


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[This message has been edited by fierosound (edited 01-06-2024).]

PhatMax JAN 06, 07:57 AM
Not a fan of continuously popping fuses….can lead to worse problems like fire. I would find the wiring diagram, locate everything that’s on that fuse circuit and start tracing wires……not fun but better than more burnt wires.