LT1-LT4 Modifications 1993-97 Gen II Small Block V8

1993 Z28, how in the world do I fix this

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Old 04-14-2013, 12:27 PM
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Default 1993 Z28, how in the world do I fix this

After I got my entire ignition system replaced ( ICM was causing massive backfires and it was misfiring so I said screw it and replaced all of it. Opti, Coil, plugs, etc ) After driving on the highway for about 10 minutes or so, my SES light will come on and then go away maybe 1-2 minutes later.

It will come back 5 minutes or so after than and then go away in a couple minutes again.

During all this, there is absolutely NO change in how the car is driving, my gauges, anything. This ONLY happens on the highway ( which I rarely take with the Camaro anyway ) I've driven around town for over half an hour on multiple occasions and I've never been met with a SES light.

For whatever reason, my SES light was not illuminating when I switched the key to ON so I couldn't pull codes via paperclip.

Well FINALLY today, I got lucky and was able to pull the code.
Code 71 : A/C evaporator temperature sensor circuit ( Open or shorted )
Which in retrospect, would make sense since my heat does take a while to get warm even though the car hits normal temp within a few minutes. Surprisingly, the A/C does work.

I can't even find this particular part on Autozone or Rockauto.com ( even though Rockauto has it listed in the search bar ) so I'm assuming I would either have to replace the entire heater core ( Which I'm REALLY not eager to do ) or am I going to have to suck it up and take it to a shop?

Just FYI, I AM currently trying to sell the car but if it doesn't sell soon, this is going to have to be fixed along with a new Catalytic Converter ( still have to take emissions in Northwest Indiana all the way back to 1976 model year )
And no junkyards around here have ANY F-Bodies for me to pull parts off of.

Last edited by Kevin Lee 487; 04-14-2013 at 12:34 PM.
Old 04-15-2013, 10:12 AM
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Changing the heater core isn't that bad REALLY, Pretty simple
Old 04-15-2013, 11:04 AM
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Originally Posted by djjab57
Changing the heater core isn't that bad REALLY, Pretty simple
That would be great if he had a problem with the heater core, but he doesn't as guppymech indicated.
Old 04-15-2013, 12:59 PM
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Originally Posted by shbox
That would be great if he had a problem with the heater core, but he doesn't as guppymech indicated.
I was going off this statement

Which in retrospect, would make sense since my heat does take a while to get warm even though the car hits normal temp within a few minutes. Surprisingly, the A/C does work.

Sounds like heater core is getting clogged, No not the problem on SES light but a problem if he wants heater working correctly
Old 04-15-2013, 02:27 PM
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Yeah, he has two problems going on, but replacing the heater core won't fix his a/c sensor problem, which it seemed he was confused about.
Old 04-15-2013, 08:55 PM
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Since we have established that the sensor and core are two separate components, how would I go about fixing this if/when I do decide to fix it? I'm mainly interested in getting sensor fixed. The heat/ac isn't really an issue to me with summer around the corner and me having T-Tops.

Extra bit of info. May just be a coincidence, but the heat never took a long time to heat up before this SES light popped up. It was a few days after the Opti & other ignition parts were replaced.
Old 04-15-2013, 11:49 PM
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I'm not sure but its worth mentioning that an A/C sensor should not turn on the SES lamp. It will store the code however. Since you seem to be having other issues related to the SES lamp(random on/off, bulb check innop.) you may have a short or failing PCM.
Old 04-16-2013, 02:08 AM
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If all of your grounds are good which sounds like that may be the case, I would suggest a PCM issue.
Old 04-16-2013, 06:24 AM
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Clear the computer code or codes and see if they reappear.
Old 04-16-2013, 09:49 AM
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DJJAB57,

Pay your debt man. Bad Chad went out of his way to help you. Do the right thing.
Old 04-16-2013, 12:41 PM
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Originally Posted by Kevin97ss
I'm not sure but its worth mentioning that an A/C sensor should not turn on the SES lamp. It will store the code however. Since you seem to be having other issues related to the SES lamp(random on/off, bulb check innop.) you may have a short or failing PCM.
Possible. The wiring in this car is a complete hackjob ( part of the reason I'm selling it )

I'm also not keen to having to put close to $1000 into the car when I'm trying to get rid of it in the first place.

But thanks for the responses guys. I appreciate it.
Old 04-19-2013, 03:14 PM
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Small update

Checked the codes again today for the hell of it and it gave me a code 63 in addition to the 71 which is odd because they're supposed to be displayed from the lowest - highest, which it did this time, but not last time.

" Right heated O2 sensor lean indicated "
I took a peek under the hood and it looks like the wires are burned off of the 02 sensor on the passenger side.

Wouldn't that make the SES light stay lit all the time? Or does it work differently on the SBCs?

Edit : Spelling is hard



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