Inf Rest Light on 1990 Corvettes

How to correctly and
inexpensively correct the ‘Inf Rest’ light on 1990 Corvettes.

The 90 is infamous for this light staying on. It seems that
there are two sensors, one on the frame underneath the battery box, and
one underneath the windshield washer container. Both bolt directly to the
frame. These little electronic wizards detect a crash via vibration in the
frame, and then set off the air bag.

The problem is two fold.
First, their location promotes getting water on them. Secondly, the water
causes a corrosion problem between the sensor and the frame. These little
wizards are so sensitive to corrosion, 1/2 of one ohm of resistance that
developes between it and the frame will send a fault light code to the
computer, and trigger the trouble light. Most of the time, the air bags
are still functional, just the light is on.

But, on to fixing
the problem…

First, let’s check the codes in your computer
to make sure this is the problem. Using a long jumper wire, jumper pin # K
on the computer link connector to ground, like the seat frame. Pin K is
the fouth slot from the left on the bottom row, or third from the right.
(The connector is under the drivers side dash). Turn on the ignition, but
don’t start the car. Via flashing engine light, you will be able to read
the codes in your computer. It will first flash a code 12 three times. The
light will flash like morse code, a long lit bulb, followed by two short
lit bulbs will be a 12. Once the three code 12’s flash, then you will
have another code, likely it will be a 25 or 26, but could also be a 15 or
16. ( , Mine (Jay) was a code 16, Indicating right side sensor) If it is
not one of these, you have a different problem, so let me know if your’s
is not one of these. Code 26 is most common, right front sensor fault.

Assuming you have a 15, 16, 25, 26 code, you will be following
the service bulletin #90-436-9J. To fix, you have to unhook the battery.
Next, remove the side panel and inner fender well cover from the front
tires. (Note, I also had to remove the tire to get to the bottom 2 torx
screws) Then you can unbolt the sensors. Next sand the frame and back of
the sensors with sandpaper, and then install di-electric grease (I found
permatex tune-up,
di-elecrical grease at Pep Boys) on the back of the
sensor, then re-install it.
After this is done, you can then reset
the computer. Now this is where the dealers have all of the problems.
Since it is very difficult to reset, they usually replace the sensors with
new ones, so they dont have to go through this. But if you can accomplish
this, it will save you bunches of green paper!!! 🙂

Taking a
jumper wire hooked to terminal K, ground it to the seat frame, and count
one thousand one. one thousand two, one thousand three. Then unhook it
from ground, count one thousand one, one thousand two, one thousand three.
Then reground it once more, and count one thousand one, one thousand two,
one thousand three. The code will disappear, leaving only a code 12 if you
are successful. If not, retry it again and again. A friend of mine did it
10 times before it was successful. But, think of the money you would have
to pay a mechanic to do THIS!!! 🙁 ( , this is where I had the most
trouble, until I got an email from Dan’s friend and late-model guru, Ed.

Here is the secret….With the ignition off. Place the jumper
wire in the K terminal and ground it to the seat frame…Switch the
ignition on and AS SOON as the light begins to flash, remove the jumper
from the frame and count 1001,1002,1003, Then reground it and hopefully
you will only see code 12’s flashing. I spent an hour yesterday doing it
wrong and tonight I got it the first try using Ed’s method. Anyway, on
with Dan’s instructions) The A/C condensor is what drops water on this
sensor, and causes the problem.

In 91 they used di-electric
grease, and the problem was fixed. As a precautionary note, do not use a
volt ohm meter to do any troubleshooting with this system. The battery in
the ohm meter will set off the air bag system. This is how mechanics get
really in deep s@#* with their boss! 🙂 As long as you can refrain from
using a meter, you will be ok.