Headlight Gremlins
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Headlight Gremlins
I'd consider myself reasonably clued up on the headlights having fitted T85s and adapted the wiring for UK operation.
Last night I shut the car down and the headlights stayed up. I cycled through on normally and then off and one light stowed. Did it again and both stowed. Weird
There are no noises so its not a gear problem. Its working fine now.
Any thoughts?
Last night I shut the car down and the headlights stayed up. I cycled through on normally and then off and one light stowed. Did it again and both stowed. Weird
There are no noises so its not a gear problem. Its working fine now.
Any thoughts?
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Joined: Aug 2003
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My two thoughts are the headlight actuator (located on the headlight bucket on the passenger side) and the switch itself. Make sure all connections are clean and tight......let us know!
Drifting
Joined: May 2000
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From: Southern NH
First thing to check is the Headlight Actuator CONTROL module located under the passenger headlight on the front of the passenger wheel well wall. It translates the ON/OFF signal from the headlight switch/BCM to a RAISE/LOWER signal to the headlight doors. The fact that one headlight stayed up during the process indicates to me it's not the switch.
Here's how the control module works. If you look at the headlight connector just behind each headlight (5 wires total). 2 are for Headlight Open/Close, 1 is for Low Beam, 1 is for High Beam and 1 is Ground for Low/High.
The 2 Open/Close wires are Lt Blue/Dk Blue for the Passenger Side, and Lt Green/Dk Green for the Driver's side.
Take the Driver's side for example, both the Lt Green and Dark Green wires always have +12V in steady state. If you have a DVMM, verify that both these wires are providing +12V even with the car OFF. Sicne they're both at +12V, the motor has a net voltage of 0V across it so it stays where it is.
To Open the headlight, the Dk Green is momentarily grounded by the control module (i.e. +12V on the Light Green, Grnd on the Dk Green). Conversely to close the headlight, the Lt Green is momentarily grounded. It appears that the control module was not doing that either because it's faulty OR posibly the connector could be having problems. The first thing to do is try to access the control module and remove/reseat the connectors (there are 2 connectors, one on each side of it). You may be able to squeeze your hand under the passenger headlight when it's up but it's tight so the best way is to remove the access panel under the bumper and reach up.
Here's how the control module works. If you look at the headlight connector just behind each headlight (5 wires total). 2 are for Headlight Open/Close, 1 is for Low Beam, 1 is for High Beam and 1 is Ground for Low/High.
The 2 Open/Close wires are Lt Blue/Dk Blue for the Passenger Side, and Lt Green/Dk Green for the Driver's side.
Take the Driver's side for example, both the Lt Green and Dark Green wires always have +12V in steady state. If you have a DVMM, verify that both these wires are providing +12V even with the car OFF. Sicne they're both at +12V, the motor has a net voltage of 0V across it so it stays where it is.
To Open the headlight, the Dk Green is momentarily grounded by the control module (i.e. +12V on the Light Green, Grnd on the Dk Green). Conversely to close the headlight, the Lt Green is momentarily grounded. It appears that the control module was not doing that either because it's faulty OR posibly the connector could be having problems. The first thing to do is try to access the control module and remove/reseat the connectors (there are 2 connectors, one on each side of it). You may be able to squeeze your hand under the passenger headlight when it's up but it's tight so the best way is to remove the access panel under the bumper and reach up.
Thread Starter
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Originally Posted by JC in XTC5
First thing to check is the Headlight Actuator CONTROL module located under the passenger headlight on the front of the passenger wheel well wall. It translates the ON/OFF signal from the headlight switch/BCM to a RAISE/LOWER signal to the headlight doors. The fact that one headlight stayed up during the process indicates to me it's not the switch.
Here's how the control module works. If you look at the headlight connector just behind each headlight (5 wires total). 2 are for Headlight Open/Close, 1 is for Low Beam, 1 is for High Beam and 1 is Ground for Low/High.
The 2 Open/Close wires are Lt Blue/Dk Blue for the Passenger Side, and Lt Green/Dk Green for the Driver's side.
Take the Driver's side for example, both the Lt Green and Dark Green wires always have +12V in steady state. If you have a DVMM, verify that both these wires are providing +12V even with the car OFF. Sicne they're both at +12V, the motor has a net voltage of 0V across it so it stays where it is.
To Open the headlight, the Dk Green is momentarily grounded by the control module (i.e. +12V on the Light Green, Grnd on the Dk Green). Conversely to close the headlight, the Lt Green is momentarily grounded. It appears that the control module was not doing that either because it's faulty OR posibly the connector could be having problems. The first thing to do is try to access the control module and remove/reseat the connectors (there are 2 connectors, one on each side of it). You may be able to squeeze your hand under the passenger headlight when it's up but it's tight so the best way is to remove the access panel under the bumper and reach up.
Here's how the control module works. If you look at the headlight connector just behind each headlight (5 wires total). 2 are for Headlight Open/Close, 1 is for Low Beam, 1 is for High Beam and 1 is Ground for Low/High.
The 2 Open/Close wires are Lt Blue/Dk Blue for the Passenger Side, and Lt Green/Dk Green for the Driver's side.
Take the Driver's side for example, both the Lt Green and Dark Green wires always have +12V in steady state. If you have a DVMM, verify that both these wires are providing +12V even with the car OFF. Sicne they're both at +12V, the motor has a net voltage of 0V across it so it stays where it is.
To Open the headlight, the Dk Green is momentarily grounded by the control module (i.e. +12V on the Light Green, Grnd on the Dk Green). Conversely to close the headlight, the Lt Green is momentarily grounded. It appears that the control module was not doing that either because it's faulty OR posibly the connector could be having problems. The first thing to do is try to access the control module and remove/reseat the connectors (there are 2 connectors, one on each side of it). You may be able to squeeze your hand under the passenger headlight when it's up but it's tight so the best way is to remove the access panel under the bumper and reach up.
