Headlights flicker on and off with heater fan speed turned up

NIGHTDRAKO33

MEMBER
2017 JEEP LIBERTY RENEGADE
2.4L
4 CYL
4WD
AUTOMATIC
57,000 MILES

Turn the heater fan speed to speed 4-7 (max) causes the headlights (and occasionally every other light) to turn on and off in rapid succession as if I was sending Morse code messages. If I'm parked with the headlights turned off, they still turn on and off with the heater fan. Everything is original including the battery and alternator but there is no corrosion of any kind messing with the connection. I can't find the ground wire though as I'm told there's more than one and I'm not mechanically inclined.

2 Replies

KASEKENNY

MECHANIC
18,907 POSTS

We need to start by checking the battery to make sure it is not low or failing.

Basically, on this vehicle when you put the load on the battery with the fan speed, the BCM is starved of voltage and starts causing all sorts of different issues.

So, let's start with checking the battery and the alternator.

https://www.2carpros.com/articles/car-battery-load-test

https://www.2carpros.com/articles/how-to-check-a-car-alternator

If this issue is only happening when the fan is on, then it could be a ground related issue but the fact that it is when the fan is on a higher speed again points to a battery issue.

So, let's start with a battery test and then we can check the ground.

I attached the location of the blower motor control module which is the ground for the blower motor.

Let me know what you find, and we can go from there. Thanks

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Friday, January 21st, 2022 AT 6:20 PM

JACOBANDNICKOLAS

MECHANIC
109,872 POSTS

Hi,

The idea that the lights flicker with the blower motor on leads me to think it's a ground. However, with the headlights turned off, they shouldn't flicker on when you turn the heater on. That leads me to think there is a short to power somewhere.

I looked through the wiring schematics for both the headlamps and the heater blower motor. Although there is more than one ground, they do have one in common.

Pic 1 is a ground for the HVAC system. Pic 2 is a ground for the headlamps. Note they have the same number, G021. That is where I would recommend checking first.

The schematics indicate they are located at the left kick panel. There will be more than one wire and they should be black in color.

The left kick panel is under the dash on the driver's side. If you were sitting in the vehicle with your feet on the floor and turned your left foot, it would touch the panel. It is behind where the hood release is located.

Pics 3-5 are the kick panel. It is clipped to the body of the Jeep (pic 5). Gently pull in those locations to remove them. Once removed, check for the black wire that is bolted to the steel body of the vehicle, checking it for corrosion, damage, and make sure they are tight.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find or if you have other questions.

Take care,

Joe

See pics below.

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