PSI harness - Check Engine/MIL light constant on

SStavin

Apprentice
Apr 3, 2015
80
33
Chicagoland
Wrapping up Dakota Digital RTX gauges and the check engine light is constant on while key-on or running. I have the MIL wire from the PSI Conversion harness running to the Dakota Digital box engine connector location. I contacted them and they said I may need to put a 1k resistor in-line. Anyone have a similar situation? I want to better understand what is going on here.
 
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fleming442

Rocket Powered Basset Hound
Dec 26, 2013
11,157
113
It sounds like the Dakota box is sensitive to what it needs as an input for the light. Or, the PSI harness is mislabeled/miswired. Unhook it from the Dakota interface, put a meter on the MIL wire from the PSI, and verify that it's working properly, first. Then, you could try the resistor.
 

fleming442

Rocket Powered Basset Hound
Dec 26, 2013
11,157
113
Checked the MIL wire with a multimeter and I'm getting 75 ohms
Uhhhhh, no. Determine whether it is a negative or positive output, and test accordingly. And, by test I mean, is it operating correctly? Does it come on with ignition on, then go dead or is it putting out a constant signal?
Have you put a scanner on it? Maybe it has a code and the light is supposed to be on?
 
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SStavin

Apprentice
Thread starter
Apr 3, 2015
80
33
Chicagoland
haha thanks for entertaining my inept electrical diagnostic skills. the MIL wire is a ground. I originally had it running to a 12v bulb and from the bulb to 12v switched power and now to the dakota digital gauges with the same results. It comes on with key-on and stays on while the car is running. I have checked for codes using the torque app+BT scanner as well as HP tuners. No codes pending or stored.
 

thesalboy

Not-quite-so-new-guy
Jul 17, 2020
5
3
Did you solve this? I have the same issue with same setup: RTX gauges, LS, PSI harness, CEL/MIL always on. I got same advice from DD, but it makes no sense to me - they are telling me to tap a 12V hot wire into the PCM signal wire - which is grounded when activated - which it seems to me even with a resistor will just short something out. It's a ground signal - how can the PCM provide some sort of "partial" ground that would cause the light to light?
 

thesalboy

Not-quite-so-new-guy
Jul 17, 2020
5
3
I haven't tried it - I'm asking SStavin whether he tried it, or otherwise how he resolved the issue.

I saw a few posts on LS1Tech referencing a resistor, but those involved putting the resistor inline with the light's power source. Can't do that here - it's all inside the DD control box.

DD says: "The resistor will prevent any type of short circuit, and since the control box draws so little current from the signal wire coming from the ECM there’s no chance that the resistor will burn up." The "signal wire" provides a ground, so I'm nervous about trying it. He said to use a "1k to 10k ohm resistor" - I'll go with 10k if I try it.

I found a post on another board that it could be a burnt trace in the ECM. I'd have to pull my entire dash out if that's what happened to me (ECM is used). Also don't want to fry the ECM trying the resistor trick.
 

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