My check engine light came on yesterday (Code 51: PROM) and then the center console started smoking. I quickly found a spot to park the car and pulled the center console off the car to see the smoke coming from the computer.

Tonight I pulled the computer case apart and found this:







As you can see the smoking is coming from a diode on the board.

**NOTE: I also tried a second known-good computer and it did the same thing, so that rules out a faulty computer.

Also, the smoking stopped after a few seconds when the 10A fuse for the gauges popped. I replaced the fuse and the component started smoking again until the fuse would pop.

Before the fuse would blow all of the gauges would work fine, so I am stumped as to what could be shorting out inside the car making the gauges fuse blow and the ECM to smoke.

Could this be a result of having the wrong PROM chip in the computer?

The ECM is a 7170, and the PROM is HWX5184

According to this site:
http://www.exatorq.com/ludis_obd1/fieroprom.html

The HWX5184 is for a 4-speed car. Mine is an automatic.

Unplug your MAP sensor, and your TPS sensor and see what happens.

I am just throwing this out there as I really dont know. But is it possible it has to do with the VSS feed that comes from the speedo to the ECM? Its crossed hot somewhere it shouldnt be or something?

I don't think so but just in case you should also unplug your TCC untill the right prom is in the ECM. The wire the 4 speed ECM sends the 'shift' light signal to on an automatic is the TCC wire. This would make your TCC lock up at weird times but shouldn't burn out the ECM.

Thanks for the input guys!!
The only problem with unplugging stuff until the problem goes away is I'll have to go through a lot of computers!! Haha

Where did you come up with the suggestion to unplug the MAP and IAC?

The ECM sends +5v power out to them. If it's the gauges fuse then I doubt it's the MAP or TPS.

There is no reason the gauges fuse would do this that I can see so I am going to say really look hard for a burnt wiring harness.

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Edit

Strike that - look at my next post

[This message has been edited by phonedawgz (edited 09-21-2010).]

Find the line that the diode feeds to on the ECM connector (and look it up in an ECM pinout chart to identify the signal) .

If it is the TCC solenoid (or some other output) then the TCC (or other load) is shorted out, shorted to ground, or shorted to another line. (as previously mentioned as a possibility)

Unplugging things until it stops smoking is an expensive way to fix this, you are better off measuring the load (resistance if you like) of each wire with an ohmmeter against the schematic with the ECM (and the battery) unplugged. A working TCC solenoid, BTW, will have a fairly low resistance, but not zero.

quote Originally posted by DavidM: Find the line that the diode feeds to on the ECM connector (and look it up in an ECM pinout chart to identify the signal) . If it is the TCC solenoid (or some other output) then the TCC (or other load) is shorted out, shorted to ground, or shorted to another line. (as previously mentioned as a possibility) Unplugging things until it stops smoking is an expensive way to fix this, you are better off measuring the load (resistance if you like) of each wire with an ohmmeter against the schematic with the ECM (and the battery) unplugged. A working TCC solenoid, BTW, will have a fairly low resistance, but not zero.

So which at which resistance would you call it bad for which outputs? Are you reading the resistance to ground? Or to the positive battery terminal?

Go here: http://web.archive.org/web/....cruzers.com/~ludis/
1227170
Schematic
Output

CR23 is a Zenier (sp?), a very basic volt regulator. Handle 1 amp by the size of it.

You have a short in something ECM drives. Pin A5 same schematic.

And note... short can be to 12v to... Check all splice/rewire from switch fiero ecm to 1227170

------------------
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[This message has been edited by theogre (edited 09-22-2010).]

quote Originally posted by theogre: Go here: http://web.archive.org/web/....cruzers.com/~ludis/ 1227170 Schematic Output CR23 is a Zenier (sp?), a very basic volt regulator. Handle 1 amp by the size of it. You have a short in something ECM drives. Pin A5 same schematic. And note... short can be to 12v to... Check all splice/rewire from switch fiero ecm to 1227170

Pin A5 is AB_SES - what do you think that means?

That it supplies the ground for lighting the SES light. Is the SES light still working? Did the SES light burn out and short? The SES light is powered by the GAUGES fuse and gets a ground via the ECM.

[This message has been edited by phonedawgz (edited 09-22-2010).]

Yes the SES light still works...

So as I look at the board the smoke seems to have been coming from U26

U26 is the driver that runs the outputs for the TCC and ALDL and AC control

The TCC gets it's power from the GAUGES fuse and grounds via the ECM

The AC relay (control side) gets it's power from the HTR A/C fuse and grounds viw the ECM

The ALDL I will assume isn't connected and will ignore for now.

So if you agree U26 is the burnt looking component, and the GAUGES fuse is the one that is blowing, it sure looks like your TCC is shorted.

[This message has been edited by phonedawgz (edited 09-22-2010).]