Dome lights (both) don't come on when door is opened, but the courtesy lights on the doors work and the map lights (all 4) work. any ideas? headlight switch has already been replaced. could it be a relay? and is there a relay for the dome lights located near the fuse box?

If the dome lights in your 2009 Cadillac CTS are not turning off, it can be a frustrating issue. Here are some steps to diagnose and potentially fix the problem:
1. **Manually Turn Off the Dome Lights:**
- In most vehicles, including the Cadillac CTS, there's typically a manual switch on or near the dome light itself. Ensure this switch is in the "Off" position.
2. **Check for Open Doors:**
- Make sure all doors, including the trunk and the hood, are completely closed. Sometimes, a door ajar can prevent the dome lights from turning off.
3. **Interior Light Dimmer Control:**
- Check the position of the interior light dimmer control, which is usually located on the headlight switch or dashboard. If it's turned all the way up, it may keep the dome lights on. Adjust it to the lowest setting.
4. **Ignition Switch:**
- Ensure the ignition switch is in the "Off" position. Sometimes, if the ignition switch is left in the "Accessory" position, the dome lights may stay on.
5. **Faulty Door Switches:**
- Each door usually has a door switch that signals the lights to turn on when a door is opened and off when it's closed. One of these switches may be malfunctioning. You can try manually pressing and releasing each door switch to see if the lights respond.
6. **Battery Disconnect and Reconnect:**
- If the above steps don't work, you can disconnect the vehicle's battery for a few minutes and then reconnect it. This can sometimes reset the electrical system and resolve the issue.
7. **Consult the Owner's Manual:**
- Refer to your Cadillac CTS owner's manual for specific information about the dome light controls and troubleshooting tips.
8. **Professional Diagnosis:**
- If the issue persists, it may be related to a more complex electrical problem. In this case, it's advisable to consult a professional mechanic or an auto-electrician to diagnose and repair the problem.
It's important to be patient and methodical when troubleshooting this issue, as it can have various causes. If you're not comfortable working on the electrical system of your vehicle, seeking professional help is a wise choice to avoid further complications.

Check fuses under the hood on driver side

The courtesy lamp supply voltage circuit of the body control module (BCM) supplies battery positive voltage to the dome lamp, the liftgate lamps, and the map lamps. When any door is opened, the door jamb switch contacts close providing a door open input to the BCM. The BCM then provides a ground to the interior lamps with the switch in the AUTO position. The interior lamps receive a ground at G401 with the switch in the ON position.
The following lamps may be manually turned ON by placing the interior lamp switch in the ON position, or by opening a door while the switch is in the AUTO position.
?€¢
The dome lamp

?€¢
The liftgate lamps

?€¢
Courtesy/map lights

You can't turn them on manually ?
This could be a BCM problem , this best left to a ASE certified repair shop or the dealer .

The following lamps may be manually turned ON by placing the interior lamp switch in the ON position, or by opening a door while the switch is in the AUTO position.
?€¢
The dome lamp

?€¢
The liftgate lamps

?€¢
Courtesy/map lights

The courtesy lamp supply voltage circuit of the body control module (BCM) supplies battery positive voltage to the dome lamp, the liftgate lamps, and the map lamps. When any door is opened, the door jamb switch contacts close providing a door open input to the BCM. The BCM then provides a ground to the interior lamps with the switch in the AUTO position. The interior lamps receive a ground at G401 with the switch in the ON position.
Important: If the liftgate is opened after all the modules go to sleep, the dome light will not come on. The liftgate ajar switch input to the BCM will not wake up the BCM once it has gone to sleep, so the dome light will not come on. Once the BCM gets an input to wake it up, from remote keyless entry (RKE) or a door handle, the dome light will turn on when the liftgate is opened.
If the driver inadvertently leaves any interior lamp ON, the BCM will turn it OFF after a 20 minute time-out.
The courtesy lamps will turn OFF immediately if the ignition switch is turned to the ON position or approximately 20 seconds after all doors are closed.
The courtesy lamps are controlled by the body control module (BCM). Inputs from the dome lamp switch and the door ajar switches are monitored by the BCM. When a door ajar switch is closed, or the dome lamp switch is turned to the ON position, the BCM supplies the B+ for the courtesy lamps.
With out a factory Tech2 scan tool or equivalent an knowing how these systems work ,you best bet is to take your vehicle to the dealer or some other ASE certified repair shop !

there are at least 3; 1 is using the dash light switch-turn all the way up;2 that show 4 lights on it-push it and it will turn them off-push it again and it will turn them on; three push on one end or the other end of the actual light.

The SJB supplies power to the interior lighting system. The SJB will set DTCs if certain circuit failures exist with the interior lighting system.
Visual Inspection Chart Mechanical Electrical

• Courtesy lamps
• Map lamps
• Luggage compartment lamp
• Vanity lamps
• Glove compartment lamp

• Smart junction box (SJB) fuse 3 (15A)
• Circuitry
• Courtesy lamps
• Map lamps
• Luggage compartment lamp
• Vanity lamps
• Glove compartment lamp
• SJB

Check fuse # 3 SJB

Check and see if the lights come on with the passenger door, if so you have a defective courtesy light switch inside the door.

yes- could be one or more fuses- either a acc or courtesy fuse or could be and int(intermintent)fuse- check all and replace with the right fuse size

Why didn't you hook into the entertainment system (radio ) ?
The one that turns on when the door opens is controlled by the BCM -body control module .You probably shorted out the transistor in side the BCM .
These lamps may be manually turned on by placing the interior lamp switch in the ON position, or by opening a door.
• The Dome Lamp
• The Rear Compartment Courtesy Lamp
• The Rear View Mirror Map Lights
The inadvertent power control circuit of the BCM supplies battery positive voltage to the dome lamp and the map lamps. When any door is opened, the door jamb switch contacts close providing a door open input to the BCM. The BCM then provides a ground to the interior lamps. The interior lamps receive a ground at G401 or G403.
If the driver inadvertently leaves any interior lamp on the BCM will turn it off after a 20 minute time-out.
The courtesy lamps will normally turn off using the theater dimming feature. The BCM provides a pulse width modulated ground to the interior lamps for the theater dimming feature. The courtesy lamps will also turn off immediately if a door lock command is received with all the doors closed, or if the ignition switch is turned to the ON position.

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Dome Lamps Inoperative
ematic Reference: Interior Lights Schematics
DEFINITION: Only the dome lamp is inoperative.
1
Did you perform the Diagnostic System Check - Vehicle?
YES - Go to Step 2
NO - Go to Diagnostic System Check - Vehicle
2
Place the instrument panel (I/P) dimmer switch in the DOME position.
Does the dome lamp illuminate?
YES - Go to Testing for Intermittent Conditions and Poor Connections
NO - Go to Step 3
3
Disconnect the dome lamp assembly.
Probe the courtesy lamp supply voltage circuit with a test lamp that is connected to a good ground.
Does the test lamp illuminate?
YES - Go to Step 4
NO - Go to Step 6
4
Connect the test lamp between the courtesy lamp supply voltage circuit and the courtesy lamp low control circuit.
Does the test lamp illuminate?
YES - Go to Step 5
NO - Go to Step 7
5
Inspect for poor connections at the harness connector of the dome lamp assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
YES - Go to Step 9
NO - Go to Step 8
6
Repair an open, high resistance, or short to ground in the courtesy lamp supply voltage circuit. Refer to Circuit Testing and Wiring Repairs .
YES - Did you complete the repair?
NO - Go to Step 9
--
7
Repair an open or high resistance in the courtesy lamp low control circuit. Refer to Circuit Testing and Wiring Repairs .
YES - Did you complete the repair?
NO - Go to Step 9
--
8
Replace the dome lamp assembly. Refer to Dome Lamp Replacement .
YES - Did you complete the replacement?
NO - Go to Step 9
--
9
Operate the system in order to verify the repair.
Did you correct the condition?
YES - System OK
NO - Go to Step 3

The interior lamps system consists of 2 main features. Illuminated entry and a battery saver feature that will turn the interior lights off after 20 minutes if they are left On with all doors closed and the ignition Off. The body control module (BCM) controls both of these functions. Battery power is supplied by the BCM through CKT 1732 to the following lamps:
• The dome lamp
• The map lamps
• The rear reading lamps
• The rear dome lamp
• The cargo lamp
• The glove compartment lamp
• The courtesy lamps
• The sunshade lamps
The BCM also controls the ground circuit side of the dome lamp and reading lamps for illuminated entry. The dome lamp and reading lamp will remain on for 20 seconds after the ignition key is removed and the last door is closed. In addition, if the vehicle is equipped with remote keyless entry (RKE), the dome and reading lamps will turn On and stay on for 20 seconds after an UNLOCK signal is received from the keyless entry transmitter.
The reading lamps, dome lamp and map lamps can be turned On at any time by moving the appropriate switch to the On position.
The rear dome lamp is fed battery voltage through CKT 1732 from the BCM, through the liftgate ajar switch, and is grounded through CKT 650 to the rear ground splice pack. The rear dome lamp will turn on when the liftgate is opened. The cargo lamp is fed battery voltage through CKT 1732 from the BCM, through CKT 744 and grounded through the decklid ajar switch.
The courtesy lamps are fed battery power through CKT 1732 and are grounded through CKT 745-- left front, CKT 747--left rear, CKT 748--right rear, CKT 746--right front. These circuits will ground through the door jamb switches. The courtesy lamp will be illuminated when the affected door is opened. For example, when the right rear door is opened, the right rear door courtesy lamp will turn on.

Not a fuse problem , if the BCM had blown fuse other thing's wouldn't be working as well . . Probably wiring or BCM . Using factory diagnostic,s instead of guessing as to what the problem is , is the proper way .

Interior Lamps Diagnosis
Symptom
Procedure
Important: Before proceeding with these diagnostics, check for DTCs. If DTCs are present, complete the associated diagnostics. If the condition still exists, return to this chart.
All of the interior lamps are inoperative when any door is opened.
Chart 1
The dome lamp is inoperative in the ON position, but OK in the door position. The map lamps operate normally.
The dome lamp switch is faulty. Replace the dome lamp switch.
The dome lamp is inoperative in the DOOR position, but is OK in the ON position.
Chart 2
The dome lamp is inoperative in any position and both reading lamps are inoperative.
Disconnect the dome lamp connector (BLK 3-way).
Check for voltage at terminal "C" CKT 1732 ORN wire.
If OK, the dome/map lamp is faulty. If no voltage is present, there is an OPEN in CKT 1732.
Either the right or the left sunshade mirror lamp is inoperative.
Chart 3
Either the right or the left rear reading lamp is inoperative in the ON or the DOOR position.
Chart 4
The rear reading lamp is inoperative in the ON or the DOOR position.
Chart 5
Battery rundown protection is shorted to ground - B1482.
B1482
The left rear reading lamp is inoperative in the ON or the DOOR position.
Chart 6