caddilac 1990


Old 03-06-04, 10:15 AM
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caddilac 1990

my engine light comes on, sometimes it stays on and sometimes it will not come on???
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Old 03-06-04, 10:31 AM
Join Date: Feb 2004
Location: So Cal
Posts: 248
check engine light

Assuming you mean the "Check Engine" or "Service Engine Soon" light (both are the same thing), when it's on it means there is an active or "hard" fault present in the on-board computer. When it is off the fault is "soft" or not active.

The code (fault) is, however, still in the computer and can be retrieved by jumping the "A" and "B" terminals in the diagnostic connector which, if I remember is located under the center dash right above the transmission hump.

With the ignition "off" use a piece of wire or paper clip to jumper between "A" and "B". Turn the key to "on" and count the flashes of the light. This will give you the "code" and tell you what circuit requires diagnosis.

Don't automatically assume the part associated with the code is bad. This is a rookie mistake. Yes, sometimes it is just the part, but often it can be something else like a bad ground, short to ground, fuel problem, vacuum leak, etc.

Once you get the code, give us a holler and we'll go from there.


Old 03-06-04, 05:19 PM
Desi501's Avatar
Join Date: Oct 2003
Location: Boynton Beach Florida
Posts: 2,207
The paper clip routine is not necessary on a Caddillac. Turn the key on then press the "OFF" button and the "WARMER" button of the A/C unit simultaniously. This will put the computer into diagnostic mode.
Press the LO fan speed (down arrow) until ACM? is displayed. Press HI speed (arrow up) until ACM codes? is displayed. Press HI fan speed (arrow up) until DTC's are displayed. Report back with the code numbers and we will try to help.

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