Triggered...Using Kaizen Relays with Aftermarket ECUs
As Kaizen Relays are beginning to ship, one particularly curious situation caught our eye enough that we thought we should share our findings:
Disclaimer: The 'issue' described below, is evident in many aftermarket ECUs, and not just the Haltech Elite 2500 that this particular customer was using. We are not placing blame on any ECU company for their internal hardware design.
Background: The customer was using a Low Side Digital Output (DPO) from the ECU to trigger a Kaizen Relay. The ECU and Kaizen Relay worked great when the car was on and running, no issues to report. The Kaizen Relays were wired to Battery Constant Power, not Switched Power.
The Issue: When the customer would go to turn the car and subsequently the ECU off, the Kaizen Relay would suddenly Turn ON.
The Reasoning: In the Haltech hardware (and many other aftermarket ECUs), each DPO is by default connected to a pulldown resistor, and can be selected via the software to use a pullup resistor instead. See below simplified circuit schematic:
When the ECU is ON and software has selected the pullup resistor to be active, the circuit becomes the following:
But when the ECU is turned off, the circuit flips to a pulldown resistor, like the following: