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I have a Electrical Issue I can no longer wrap my head around... I am officially very confused.
A couple days ago I Noticed my Cruise Control would not set. The main was on but no set, and then it would randomly enable. I then started tapping the brake pedal randomly and sometimes that would set me set the cruise. So I assumed my Brake Pedal Switch was faulty and replaced it. It took 2 mins and cost $26 or something like that (OEM part). Still no cruise control.
Then I noticed something odd, my shifter can move without pressing the brake. Only while the key is the 2 position or the Car is on. AND when the Head light switch is moved from off to the FIRST position (the one that turns on tail lights and side markers). So, When I turn the lights off with the key in 2 the interlock solenoid clicks and locks the shifter in park. and when I turn them on the solenoid unlocks it without me pressing the brake. With lights on my brake pedal does nothing to stop it from shifting.
Here's where it gets weird, randomly the cruise worked so I pulled over, went into park, checked and I noticed the Headlight switch no longer controlled the interlock solenoid. So I turned the car off, and put the key to 2. Everything was fine, Switch still does nothing. I held the brake down or a few seconds with the tail lights on and then BOOM the headlight switch now controls the interlock solenoid again.
Lastly, I noticed in the 2 position, turning the headlight switch on and the interlock solenoid unlocks but It locks again when I Press the accelerator, then locks when I let go of the accelerator. I have no tested this with the car on but regardless... Weird
I cannot figure out what it is!! Is it maybe the tail light bulb? but how could a bad bulb be giving more power to trigger the interlock solenoid?
All I could find is a diagram of the Interlock System in the manual
When weird stuff like that happens it's usually bunch of broken wires or water in some control module. Since most of the stuff involved is inside the car, I doubt mice or some moving part had a chance at the wiring loom.
Shift lock solenoid is controlled by PCM. PCM also gets input from the brake pedal. It does eventually gets input from the cruise control switches, but that actually goes through gauge cluster first.
Water in PCM is not that uncommon if ac / moonroof drain gets clogged. However, for most of the people on this forum, water in PCM will melt ignition coils.
I think getting into PCM would be my first step all things considered, well not counting connecting the scan tool and letting it rear all modules in the car (as car sometimes sets codes for lost comm etc. that might give me an idea where to look next). You might be able to see water damage / moisture without even getting the PCM out.
I don't know why headlight switch plays a role here. It seems like headlight circuit doesn't really meet with PCM. Maybe MICU is actually diving in water and somehow affecting the rest of the system?
Don't really have any other idea right now.
There is couple things I glanced over when reading your post. Might be useful.
@peter6 I just noticed my tail lights don't say on but the left LED panel is very weak compared to the right. and when braking several led's are not lighting up. You think it could be a bad led panel in the tail light?
If only one light is affected, then most likely tail light is going bad. I've seen couple TLs on the road with burned out leds in the tail lights.
If it would be shorted / causing heavy load, most likely all brake lights would be affected, and then either fuse or brake light switch would go. Technically turning on the headlights would reduce load on the brake light switch circuit, but once again, I think both taillights would be affected.
I don't think it's related, but it should be easy to disconnect suspect tail light and do a test drive.
If only one light is affected, then most likely tail light is going bad. I've seen couple TLs on the road with burned out leds in the tail lights.
If it would be shorted / causing heavy load, most likely all brake lights would be affected, and then either fuse or brake light switch would go. Technically turning on the headlights would reduce load on the brake light switch circuit, but once again, I think both taillights would be affected.
I don't think it's related, but it should be easy to disconnect suspect tail light and do a test drive.
Yup, it was a bad Tail light housing. Turns out the aftermarket housing I got was the problem since we have a wire from inside the housing going into the LED panel. So I bought a OEM tail light and put it in, and boom solved. Can't even trust a single aftermarket cable to not go out...
Yup, it was a bad Tail light housing. Turns out the aftermarket housing I got was the problem since we have a wire from inside the housing going into the LED panel. So I bought a OEM tail light and put it in, and boom solved. Can't even trust a single aftermarket cable to not go out...
OEM goes out too.
The tail lights are wired as part of the cruise control module. Which is why you can sometimes set it in the day time but they go ineffective when you switch to your parking lights. It's same reason why they wouldn't work if your brake pedal position sensor or 3rd brake light has gone bad. It's super common for the tail light LEDs to die out. Looks like broken teeth.
01-06-2022, 09:50 PM
