Don’t agitate the immobiliser -- power source for LED DRLs

This post is about risk associated with jumping off the 10A IGN fuse in the engine.

I installed 2018 headlights/assembly in 2016 Tundra SR5 with halogen type DRL. Jumpered off the 10A IGN fuse/circuit in the engine bay. Although rare, several times it made the immobiliser circuit unhappy. For theory on why, See attached pages from service manual: 1) lists all the circuits that operate on the 10A IGN fuse; 2) shows the associated wiring diagram.

This video https://youtu.be/mGGQMxqLDRI shows step one in relocating to a better IGN 12V connection point.

Then step two: https://youtu.be/fqohGtJenwQ.


Initial plan to tie into the DRL hardwire from Main Body ECU to Flasher Relay module proved to be a flawed approach, as this circuit drops to ~0.8V when the DRL is on. So tied ultimately into the Flasher Relay J29 connector pin 3 (7.5A LH-IG) line as shown in this video https://youtu.be/szT5W0YPPdk.

The theory is the risk of agitating the immobiliser circuit has now been removed

 

FYI... This is a link to the LED DRL wiring harness I used: https://automotivecustomlighting.com/store/toyota-tundra-oem-led-conversion-2014-2020/

 

Why do I think the Immobiliser system was unhappy? ... Glad you asked...

I don't have TIS, thus somewhat handicapped when diagnosing the problem. The symptom however is:

• crank but no start (out of the blue)
• turn key off, then back on; and notice check engine light isn't lit
• attempt to read code with ODB scanner and get a link error

Learned at this point need to get back to point where check engine light comes on when key is on (as normal). Disconnect battery to make this happen. (Usually wait 30 seconds for capacitors to drain. And after reconnecting battery, leave ignition switch on for ~5 seconds before trying to start.[see hint below]) Once engine light is functioning correctly (i.e., being on when key is switched to ON) engine will start.

And, Why do I suspect immobiliser system (IS)? While I can't provide specific proof (thus this remains theory ), I had 2018 headlight LED DRLs powered with a jumper fuse holder directly off the 10A IGN fuse in the engine bay. Attached are a couple pages from the service manual implies the IS checks this circuit as part of its power on self test. (Also the ~80 pages entitled "Title: ENGINE IMMOBILISER:" in the service manual describes no shortage of secret handshakes, waveforms, and "hints" ... making it clear the IS logical is complex and proprietary to say the least.)