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Discussion Starter · #1 ·
How would know if your ECM/PCM is bad on 94 Impala SS? I’m having electrical issues but I think my computer went bad…
 

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How would know if your PCM is bad? ... having electrical issues but I think my computer went bad …
Either by:
1. definitively eliminating every other possible electrical problem before suspecting the pcm
2. checking the pcm for trouble codes (why do I think it's Error 54?)

Since you have a '94 & a '96, you can TEMPORARILY use the '94 to operate the '96 SS.
This will throw Error 43 Knock Sensor Diagnostic.

What other codes does the OBD1 pcm throw?
 

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You could get another computer from the local P-N-P junk yard. There is a 94 RMS and a 94 FW in local yards here.
 

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Maybe elaborate on your exact issues first and see if there are codes before trying a different PCM.

If your PCM has failed output drivers
( maybe wrong terminology)
it is possible an issue with the car killed them.

If swapping PCMs , I would personally try yours in a diff car as there is a small possibility your car could hurt a different PCM.
SMALL possibily yes , but ,,,
 

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Discussion Starter · #6 ·
How would know if your ECM/PCM is bad on 94 Impala SS? I’m having electrical issues but I think my computer went bad…
Lots of issues…. Started in March of 2021 and progressively have gotten worse….
  • · Very bad Idle
  • · Transmission not shifting
  • · Secondary fan not turning on
  • · Primary fan constantly running
  • · Volt meter on dash moves with when idle drops
  • · When blinker is put on – makes volt meter on dash moves to the sound of the blinker.
  • · Check engine light on – cannot read code *
  • Three different scanners cannot communicate
  • Rear speakers do not work

 

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Discussion Starter · #7 ·
Lots of issues…. Started in March of 2021 and progressively have gotten worse….
  • · Very bad Idle
  • · Transmission not shifting
  • · Secondary fan not turning on
  • · Primary fan constantly running
  • · Volt meter on dash moves with when idle drops
  • · When blinker is put on – makes volt meter on dash moves to the sound of the blinker.
  • · Check engine light on – cannot read code *
  • Three different scanners cannot communicate
  • Rear speakers do not work
Items I have replaced/repaired in the past 12 months
  • · PCV value replaced
  • · Ignition coil replaced
  • · “ICM” Ignition control Module replaced
  • · “IAC” Idle air control value replaced
  • · “EGR” valve replaced
  • · “EGR” valve solenoid replaced
  • · Coolant flushed twice
  • · Fuel Filter
  • · New relays for both primary and secondary fans
  • · Throttle body gasket
  • · Throttle body position sensor
  • · 8 new spark plugs and wires
  • · Mass Air Flow sensor


NOTE : Opti Spark changed in 2019
 

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Discussion Starter · #8 ·
Note: cleaned the grounds on the starter, alternator, ignition coil, battery, passenger fender. Checked the grounds under rug on drivers side… all clean… volt meter check on all grounds and all in the 12volt range.. no fluctuations…
 

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If swapping PCMs , I would personally try yours in a diff car as there is a small possibility your car could hurt a different PCM.
SMALL possibily yes , but ,,,
Before sacrificing a different PCM to this car have the alternator checked for bad diodes and the battery checked for proper operation.

Have you been "boost starting" the car? Has the battery been depleted to low voltage and left that way for days or weeks?

volt meter check on all grounds and all in the 12volt range.. no fluctuations…
Check that the ground and power connectors can supply amps to the PCM. A volt meter will not always show a bad ground. A common way to check for bad power or ground wires is to use a headlight bulb to load the wiring with 5-10Amps.

The ground connections to the PCM are very important as they are used to control injectors, transmission, radiator fans, etc.

The most important things to be sure of with testing ground wires are that at rated current (amps) that the wire from one end to the other is not "dropping" voltage. (you could measure this) Bad wires and ground connections become resistors and reduce voltage to the equipment they are connected to and cause hard to diagnose issues.
 

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Wow that's one hell of a issues list. Being a 94,have you replaced the zinc aux battery post that sits along side of underhood fuse center?
My 94 started showing strange electrical gremlins......the zinc aux post was heating up.Replace it with the brass 95/96 upgraded bolt/stud unit.

Also,last year a B Body friend was having all kinds of crazy symptoms like yours.Long story short,he too thought pcm was bad.
Turned out to be broken ground wires from pcm, to left front cyl head ground stud at coil mounting. There's 4 ground wires(one for each plug) coming from pcm,they all go to one gang connection in the left side engine harness.Approx 8cm from the grounds break out to coil bracket. I'd check this,very easy to do a visual. It's a 4 into 1 crimp of black and blk/wht wires.

Here's a couple pics I took that point to approx location,and a pic of the description of location in service manual.It's the bottom one listed,S119.
Jim
 

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If your '94 SS pcm can operate the '96 SS properly (except for Error 43 Knock Sensor Diagnostic), that would point away from the pcm, & toward wiring & grounding issues.
 
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