CEL P0690 after DD gauges

[Ghost's68]

Hello everyone!

Just installed my DD HDX gauges into my 68. Using a BIM-2 module to read info, it is LS swapped using a E38ECM and T42 TCM. Oddly enough after the install, I’m getting a P0690 code, ECM/PCM Power Relay Sense Circuit high.

Prior to install no CEL of any kind were being thrown. I powered the gauges doubling up the radio power via the Cig lighter and radio connectors on the fuse block. Used the factory ground that was on the OE gauge connector. I even tried using a 16g wire and relocated the ground, still having the same issue. With the code cleared, if I start the truck up with the DD gauges UNPLUGGED into the OBD port, no check engine light is thrown. I can connect the BIM to the OBD after the truck is started and still no CEL. It only throws it if I start the truck with the BIM PLUGGED into the OBD port.

What am I missing here guys? Any help is appreciated. Thanks everyone in advance

[BR3W CITY]

Is it able to operate the gauges, and can it communicate with the BIM?

[Ghost's68]

Yes it connects to the BIM and pulls the data. Getting temp, oil, tach and other various inputs. It won’t read what gear it’s in though.

[BR3W CITY]

Try swapping out your IGN relay, or smacking it with a screwdriver. It sounds like your getting voltage to the IGN relay even when the car is off, which triggers the code. The factory descriptor says more than 2v with the IGN off should trigger that code.

You might have a bad/stuck/corroded ign relay, or you have a wiring short leaking voltage on that circuit.

I'd also consider powering the gauges from an alternate 12v source and seeing if anything changes.

[Ghost's68]

Originally Posted by BR3W CITY

Try swapping out your IGN relay, or smacking it with a screwdriver. It sounds like your getting voltage to the IGN relay even when the car is off, which triggers the code. The factory descriptor says more than 2v with the IGN off should trigger that code.

You might have a bad/stuck/corroded ign relay, or you have a wiring short leaking voltage on that circuit.

I'd also consider powering the gauges from an alternate 12v source and seeing if anything changes.

Thanks Brew for the help so far.

So I checked to see if the ign wire going into my relay box was getting voltage with the truck off, it was reading zero. Started it and jumped up to 12-13v. Should I be checking this wire or is there another one? I also changed the ign and constant power sources. Still the same issue.

I am running a modern vintage systems standalone harness BTW.

[BR3W CITY]

The ECM interfaces on the ground side of that relay, so I'd doublecheck all your grounds. Are you getting full charging from your alternator? The thing thats throwing me is that its only when the gauges are plugged in.

[Ghost's68]

Originally Posted by BR3W CITY

The ECM interfaces on the ground side of that relay, so I'd doublecheck all your grounds. Are you getting full charging from your alternator? The thing thats throwing me is that its only when the gauges are plugged in.

Yea double checked all the grounds. Even played with different grounding on the gauges. Reading about 13.7v when charging, which seems about right. I made a video just earlier to show the problem better then I could prob type it out. Check it out and let me know what you think. It’s a bit long but I try and cover all of it. I’m at a loss. Truck still pulls hard and doesn’t seem to be “real”.

https://youtu.be/rYBI8dKHIm0