Turning it on
On the Check Engine Light wiring page, Light Output switches the function on or off. Once it's on, Output Mode sets where the signal goes.
Picking an output mode
| Output Mode | Use it when | What you need |
|---|---|---|
| Digital - Switched | You have a standalone warning lamp or LED | A spare DPO wired to the lamp |
| CAN Output - Switched | You want the factory cluster's own check engine lamp to work | A CAN connection to the factory cluster |
| Haltech CAN Supported Dash | You run a Haltech dash that supports it | The dash on the Haltech CAN bus |
Wiring a lamp to a DPO
ECU digital outputs normally switch to ground, so feed the lamp from switched 12V and let the DPO complete the circuit. Most small indicator lamps and LEDs are fine on a DPO directly. For anything that draws real current, use a relay. Test it by making the ECU turn the light on in NSP before you close up the dash.
A check engine light that stays off all the time might mean a blown bulb or a broken wire, not that everything's fine. Recheck the lamp from time to time, especially after any dash or harness work.
What turns the light on is set in the check engine light settings. Codes are listed in the DTC index.
