CEL box function

[81cutlass]

Working on integrating my 87 grand national dash harness into my 85 cutlass dash harness.

The c437 plug is what goes from the ECM to the OBD2 plug, ECM power, VSS and check engine light among other things.

Connector Pinout Diagrams

Turbo Regal Performance Recipes

www.gnttype.org

I'm good on everything except this random green box from the 307 dash harness that's in my cutlass. I also have a spare from my 305 2+2 dash harness.

What does this box do? It has power, ground, and check engine signal from the ECM on one side (white/green) and yellow to the gauges on the other side.

I don't believe GN's had this but I can't confirm. Reason I say that is the c437 pinout for location C is green/white on the 307 harness which uses this box, but the GN pin c which is still check engine light is brown white and I don't believe it uses the box.

Can I just cut the box out or???

 

[PVDave]

Can I just cut the box out or???

Without a signal from the PCM (on the white/green wire), the green box grounds the yellow wire, which illuminates the check engine light. So the default condition is CEL ON, until the PCM commands it off.

I think GM used this box to keep people from cutting the green/white wire at the PCM to defeat the check engine light.

If you cut out the entire box, the CEL is dead. If you connect the yellow wire to the brown/white from the GN PCM, the CEL should work normally.

 

[81cutlass]

Without a signal from the PCM (on the white/green wire), the green box grounds the yellow wire, which illuminates the check engine light. So the default condition is CEL ON, until the PCM commands it off.

I think GM used this box to keep people from cutting the green/white wire at the PCM to defeat the check engine light.

If you cut out the entire box, the CEL is dead. If you connect the yellow wire to the brown/white from the GN PCM, the CEL should work normally.

Awesome, thanks!

I dug quite a bit for the info on that box and couldn't find anything.

Makes sense, I won't feel bad cutting it out.