CEL, GMPP harness for LS3
 

Does anyone know if the "Check Engine Light" on the GMPP LS3 harness is triggered by a negative source ?? My new gauges CEL needs a positive trigger for the light to turn on. I know I need a relay to convert from neg to positive. I just wanted to confirm the negative source for the CEL. Thx.

What gauges are you running? I am currently running the VHX gauges and just have the CEL wire from the GMPP bulkhead wired directly into their control box. I used the have an LT1 (before the LS3) using an another companies EFI harness and it did provide the negative side of the circuit from the PCM side. I just had to hook the other side of the LED to an IGN source.

Typically you supply the CEL with a keyed/fused +12V circuit. The ECM switches a negative signal to the CEL when a DTC is set. Easy way to check if you have HP Tuners is to toggle the CEL with the software.


T,

Thanks guys for the reply. I'm using New Vintage Gauges 69 series 3 in 1. The gauges call for a positive trigger (12V) on the warning lights. I know the parking brake is triggered via a ground. I will be using a relay to convert neg to positive for the brake light in the gauge. I also think the CEL is triggered via a ground, so in order for the CEL to light up in the gauge I have to convert it to positive, (another relay).

I am not sure that the CEL signal can drive a relay. What is the coil resistance of the relay you are using?

Don

You know Don I am not exactly sure. Typical 30a Bosch relay. The relay is just converting from negative to positive trigger (reverse polarity)

I guess you can try and see if it works. 30A is a bit of overkill for this application. :D

Something like this is all you need:

http://www.ebay.com/itm/2pcs-Blue-41...QAAOSwT6pV4XRo

Don

I agree the 30a is overkill. That small signal relay looks pretty good. Hmmm.

You could also use a simple single transistor inverter. Not sure if you are comfortable with wiring something like that. I have the same gauges and will go that route when I finally get to wiring them up.

Don

This Bosch 12V 30A relay has a coil current of 160 mA which is a lot more than an LED.

http://www.texasindustrialelectric.c...0332209150.asp

I will dig around and see if I can find the CEL current capability.

Don

Thanks Don !!!! So the Bosch relay may work ??

No I think it requires considerably more current than an LED and as such it may not be able to sink enough current to turn the relay on.

This is all I could find regarding MIL current capacity:

This circuit requires any 12v low current light and an ignition 12v power source. The ECM MIL output supplies the ground for the circuit.

I am not sure that 160 mA would be considered a low current light.

Looks like all you can do is try it and see if it works. Sorry I could not be of more help other than raising questions.

Don

Hey, thank you very much !!! FYI Don, I'm also over on Team Camaro. I asked the same questions over there LOL. Thx again.

How about this little solid state relay? If I am reading it right you can use a positive or negative trigger. Just connect the negative trigger input to the MIL signal and add a 4.7kohm pull-up resistor to 12V. Then use the relay as you had planned.

http://www.ebay.com/itm/1-Channel-SS...QAAOSw4SlV8f4-

Don

why can't you just give the light constant power and hook the ground to the check engine light wire? Thats what i did

Don, just curious. The picture I saw on New Vintage's website showed a CEL in the right side gauge. Why not use the one already built in? Are you 100% sure that the CEL requires the POS signal? Just seems weird that the industry standard is a Neg signal from the PCM and New Vintage is totally different. Just seems like alot of trouble to go through for the light to work.


http://www.newvintageusa.com/images/69-set-lit.jpg

Yep, that's the one. It calls for 12V positive.

For whatever reason the gauge wants a positive drive for all the indicators. Both LED pins are not brought out, only the positive side as far as I know. Why they didn't do their homework is a bit of a mystery. There may even be a controller between the input signals and the LED's.

Don

Because you don't have access to both LED pins.

Don