Anyone know why check engine light wont come on?

[Scott]

So my truck will not pass smog in ca because the check engine light wont come on. I checked the fuses and the horn fuse was blown, as soon as you put a new one in it blows. Are these related? Anyone know what this could be? Thanks
1986 k1500

 

[Chevyboy12]

Check the bulb alot of times it blows out

 

[MrMarty51]

Maby conditions havent given it a reason to come on.

 

[HotRodPC]

Maby conditions havent given it a reason to come on.

It's supposed to come on with Key On, motor not running. This also tells the smog test technicians that it's functional and not been disabled. If it's on after the engine starts then he also fails.

 

[89Suburban]

I'll have to look at my wire diagrams when I get a chance.


Posted From Hell

 

[chengny]

Some basics to check - fuses and ground connection:

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[towjoe]

change wiring around and use it as a charge light lol comes on when key is on and goes right out when started.

 

[chengny]

Diagnostic charts and trouble shooting procedure:

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CHART A-5 - "SERVICE ENGINE SOON" LIGHT INOPERATIVE



Test Description :

1.This checks for open gage fuse or open in "SERVICE ENGINE SOON" light circuit, including IP connector, printed circuit, and "SERVICE ENGINE SOON" lamp.
Normal response is lamp "ON".



2.This checks for a shorted ECM.
Grounded ECM terminal "G" will turn the "SERVICE ENGINE SOON" OFF". If disconnecting ECM turns light "ON", ECM is shorted. Normal response is lamp "ON".



3.This checks for grounded wire from terminal "C" of lamp driver to terminal "G" of ECM, an open circuit to terminal "B" of lamp driver, a bad ground or faulty lamp driver.
A normal reading is about 9 to 11 volts because of the drop through the upper resistor in the lamp driver. Over 11 volts indicates there is no drop in the lamp driver.

This indicates a bad ground or faulty lamp driver.



4.This step checks for an open in the wire to terminal "B".
Normal voltage is approximately battery voltage.



4A. This checks for an open wire to terminal "E" from the "SERVICE ENGINE SOON" lamp. With terminal "E" grounded, the lamp should normally light. Lamp "OFF" indicates an open, and lamp "ON" indicates faulty lamp driver connection or lamp driver.

5.This checks for a grounded wire from driver terminal "C" to ECM terminal "G". Normal response is light "ON".




THIS MAY NOT EXACTLY PERTAIN TO YOUR TRUCK BUT SHOULD BE OF SOME HELP.

 

[89Suburban]

Posted From Hell