Help! '90 C4 Diagnostic Code Interpretation

[Spinman]

Where in the service manual is the area that would list the various codes received when flashing the ALDL - I can't find the section...

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Returned to the car after lunch - and it would not start.
Click - Click - Click

Had somone jump me, and the car started immediately.
During the drive home, experienced one power surge - almost felt like it was going to stall and I goosed the idle a bit.

Checking the gauges - everything seemed in the normal range. My initial thought was with today's high temperatures (95+) - perhaps the age of my battery gave into the heat (or that the alternator experience the dreaded underhood failure due to temperatures), but didn't notice that the volt gauge was behaving badly.

However, I did notice that the Speedometer display panel started to flash "sys-sys" with a pause then then "sys-sys" again. This continued the remainder of the drive home. There were no other inticators illuminated(such as SES).


When I got home, I jumped ALDL pins "A-B" and flashed "1-2" "1-2" "1-2" "1-2" 1-2", etc - indicating no stored codes.

I then jumped the ALDL pins "A-G" and received the following output on the Speedometer Display Panel:

A very small "1" on the top while the following display occured below in a larger font:

H31
H33
H35
H37

At this point, the small "1" changed to a small "4" and where the larger numbers were display - they were replaced with 3 dashes "---"

At this point, the small "4" changed to a small "10" and the bottom line was redrawn again with 3 dashes "---"

I did not notice any additional information after this point in the display. It continued to show the small "4" and the 3 dashes "---"


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Hoping someone will be able to interpretate this display in conjunction with my starting problems and point me in the right direction.

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BTW - I just purchased an Innova Equus 3140 Scantool that supports both OBD1 and OBD2. I checked the literature before purchase, and with technical support after I took delivery, and both sources indicated that it would work with my 1990 Corvette.

With the Key in the on position - when I plugged the unit into the dash, it recognized that I had an OBD1 system and told me to push the linkup button to read the system. When I pushed the button - there was a loud click and the vehicles power seemed to be "rerouted". I don't know what actually happened, and how to better describe it - but the bottom line is that the 3140 Scantool would not read the computer and instead seemed to reset something in the electrical system.

 

[Spinman]

Digging around, I've discovered:

1) That the Hxxx means history - so no apparently code currently active

2) When all else fails, the flashing sys message with no set codes often occurs with a low voltage situation

So I probably have a weak battery that was affected by the underhood temperatures during todays hot weather.

I disconnected the battery and put a charger on it overnight. I'll see what happens tomorrow...

 

[Hib Halverson]

Your IP display was telling you there are a bunch of CCM history codes set and they relate to various timing signal functions associated with the LSD display. As they are history codes, first thing to do is to clear codes and road test.

The procedure to clear codes is in the CCM section of the factory service manual.

If the codes don't come back, don't worry. If they reset, the solutions, which will either be to repair various wiring or connections or replacing the CCM, are in the FSM.