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I own a 94 Honda Accord LX 4dr, 4 cylinder 5 speed MT model.
I recently decided for some insane reason to replace my interior dome light with an LED. I searched for some time and finally decided on a replacement, ordered it and it came in today.
I figured this was a simple job, remove lens, remove old incandescent lamp, install new LED (checking for polarity), replace lens cover, job done...
Everything went fine until I went to replace the lens cover when all of a sudden the LED went out (drivers door was open, switch set to "door" operation). I noticed the drivers side courtesy lamp was out, so figured I had somehow blown a fuse. Sure enough the fuse was toast, so I switched it to the off position and replaced the fuse.
Got back into the car and switched the dome light to "door" and nothing, looked at the courtesy light and it was again off. Switched it to off and replaced the fuse again.
At this point I decided to remove the dome light and take a closer look. At first I decided I must have just gotten a bad LED, but it did light up initially. Upon closer examination, I discovered what the root issue was. The large rectangular body portion of the new LED, when pushed fully down into the retaining clamps would short out the two retaining clips lower edges, which were closer together than just the upper retaining portion.
I was able to disassemble the lamp holder and trim back the metal that was causing the short and put everything back together again to retest.
This is where I'm currently at... The LED will light up fine when the dome switch is in the "ON" position, but not when the drivers side door is opened with the dome switch in the "DOOR" position (middle). I've done some trouble shooting and tried to follow the wiring diagrams to understand the problem better. What I have found is:
1) The courtesy door light works fine, coming on and going off when the door is opened/closed.
2) The dome light WILL come on fine in the "DOOR" switch position if the passenger side door is opened.
3) The drivers side "door open" light in the dash safety indicator also does not light up any more for the drivers side door, but works for all others.
I believe I have damaged the wiring somewhere from the short condition, but I'm not sure where the damage is at. Since the LED lights up fine when the passenger door is opened, I believe the door wire from the dome fixture to the car is O.K.
My thinking is that the only place in the wiring diagram where I can see this problem occurring is probably on the printed circuit board that is a part of the gauge safety indicator. I've had the gauges out before and of course it's a royal PITA, but the only other place it appears the problem could be, would be in the Integrate Control Unit. The purpose of this unit is not clear to me, but for the life of me, I can't seem to figure out how to unplug the firewall side plug from the unit, before it can be unplugged from the under dash fuse box. Likewise unplugging the wiring harness from the door seems nigh near impossible.
Has anyone been down this road before? Should I just bite the bullet and pull the dash gauges out and look for a fried etch on the circuit board? As much of a PITA that it is, working in that cramped space where the under dash fuse box/ICU is, may be worse. I'm a "plus" sized guy, working in a tiny space. I recently had to replace the small rubber plug on the back side of the clutch petal that operates the starter interlock feature, and eventually had to pull the entire clutch petal assembly out to reach the impossible location of that minor part...
My other hesitation with removing the gauges is that I've had an issue with a flakey lamp not illuminating properly in the gauge array, but currently all are working great, so I hate to touch it again! But if that is where the problem lies, at least I've been there... done that... before.
You can pinpoint where in the circuit the short is by checking continuity with the multimeter. Start with the wires. If you have continuity on your wires then that only leaves the gauge unit or MICU as the cause.
The MICU (Multiplex Integrated Control Unit) is built into the under-dash fuse/relay box and allows the use of very small wires to all the accessories. Otherwise you would have a wire bundle the size of your fist instead of the size of a quarter. If you blew the MICU the you'll have to replace the entire box ($$$).
Unbolt the fuse/relay box and pull it out as far as you can. You should then have just enough space to access the back of the box.
You can pinpoint where in the circuit the short is by checking continuity with the multimeter. Start with the wires. If you have continuity on your wires then that only leaves the gauge unit or MICU as the cause.
The MICU (Multiplex Integrated Control Unit) is built into the under-dash fuse/relay box and allows the use of very small wires to all the accessories. Otherwise you would have a wire bundle the size of your fist instead of the size of a quarter. If you blew the MICU the you'll have to replace the entire box ($$$).
Unbolt the fuse/relay box and pull it out as far as you can. You should then have just enough space to access the back of the box.
5th generation Accords have an integrated control unit (ICU) that is separately replaceable; the whole fuse box does not need to be replaced if the ICU was faulty. There are just regular sized wires connected to the ICU.
It is more likely an open (break) in the circuit instead of a short.
5th generation Accords have an integrated control unit (ICU) that is separately replaceable; the whole fuse box does not need to be replaced if the ICU was faulty. There are just regular sized wires connected to the ICU.
It is more likely an open (break) in the circuit instead of a short.
Did not know that. Must be nice, those things can get expensive. It should make it easier to diagnose.
No doubt that I now have an open circuit as a result of the initial short caused by the metallic body of the replacement LED dome light.
The fact that the driver's side courtesy light still works and the dome light still works from the passenger door switch indicates to me that the basic car wiring is still intact.
I have no idea what the internals of the ICU is comprised of, but I have seen the gauge circuit boards closely, and smoking one of the thin etches seems highly probable. I just don't clearly understand where the actual ground comes from for the door switch supplied dome light activation, and I'm not clear on the exact role of the ICU in the whole picture.
I was hoping if the ICU could be easily unplugged, I could examine the internals to look for a burned etch or fine wire. Perhaps it can't be examined.
I could see the one bolt securing the fuse block. Do either of you know how many are used to secure it to the vehicle?
1. The ground signal from the driver’s door switch is used for more than just the driver’s door courtesy light, dome light, and dash door open indicator. It is also used as part of the headlight reminder circuit, key-in reminder circuit, power window key-off timer system (open driver’s door cancels the delay function), and entry light timer system light. With the exception of the driver’s door courtesy light, the driver’s door ground signal goes to/through the integrated control unit for these other circuit/functions.
2. Although the door indicator on the dash does not work, does either of the following reminders work?
• With the key in the ignition (position Accessory (I) or Lock (0)) and driver's door open, does the key-in reminder chime?
• With the key in the ignition (position Accessory (I) or Lock (0)), headlights on and driver’s door open, does the headlight reminder chime?
If they work, the driver's door switch probably has sent a ground input to the ICU. If not, then the ground input from the driver's door switch may not be getting to the ICU.
3. The driver's door switch connector is located at the left B-pillar, and the Grn/Orn wire is part of the left side wire harness; where it splices off to following connectors:
• the Grn/Orn wire is part of a harness connector at the driver’s door jamb for the driver’s courtesy light
• the Grn/Orn wire also runs directly to the rear of the under-dash fuse/relay box. The Grn/Orn wire is part of a harness that plugs into the back of the under-dash fuse/relay box; via a 12P blue harness connector (terminal no. 1 of the connector). The 12P blue connector at the rear of the under-dash fuse/relay box connect directly to terminals at the front of the under-dash fuse box for the integrated control unit (ICU located at the front of the fuse/relay box).
4. You can test whether the ground signal is passing through the Integrated Control Unit. At the front of the under-dash fuse box is an 18-P blue connector (Connector C602), a Grn/Orn wire at terminal no. 7 of Connector C602 is where the ground signal should come from the ICU with the driver’s door switch when opened. The wire here has passed through the ICU and is going to the instrument gauge panel – You can test for continuity to ground on the Grn/Orn wire at Connector C602 harness terminal no. 7; or for continuity between the wires from the door switch to Connector C602. If there is no ground signal at Connector C602 terminal no. 7, then you may want to test if there is the ground signal coming to the ICU.
5. The integrated control unit can just be unplugged from the under-dash fuse box, without removing the fuse box. (A 16P green harness connector is disconnected from the side of the ICU, then the ICU is just unplugged/pryed gently from the front of the fuse/relay box.)
With the ICU unplugged from the under-dash fuse/relay box, and the driver’s door opened, you can test whether the ground from the driver’s door switch is making it to the ICU. Terminal A1 (upper-left hand corner terminal where the ICU was previously plugged in is where the ground from the Grn/Orn wire feeds into the ICU). – There should be continuity to ground at terminal A1 with the driver’s door opened.
Thanks so much for all the detailed information! That's great stuff and will be a great help in running down the problem.
I have removed the ICU and preformed a detailed inspection including doing a test of all the diodes on the module. No apparent damage was detected so far, but I decided to cut it short due to being Mother's Day!
I'll pick it up tomorrow and do the additional testing of driver's side door switch functioning to see what functions do or don't work.
I see that there are several integrated circuits on the ICU module that I suppose are involved with the additional functions. When you mention testing for continuity to ground at various points, is this passed directly through, or is it a "logical" ground supplied by active components. In other words, is this something I can measure from those points to the chassis with power off, or should I be taking a voltage check to determine a near 0 voltage with power on? Considering the dome light would normally come on with the ignition off, I would guess it's a direct pass through, or else the ICU must have power always supplied to it, as long as all the fuses are installed.
More updates tomorrow. Again, thanks so very much for the detailed help!!!
#2: with everything plugged back in, if the headlight reminder chime or key-in chime works, the ground from the driver's door switch went through to the ICU.
#4: With the driver's door open, ground (-) should go from the door switch to the ICU. This test at Connector C602 is at the Grn/Orn wire after it passed through the ICU. You touch one of the ohmmeter's lead to the Grn/Orn wire terminal here and other other ohmmeter's lead to body ground (such as a ground bolt or bracket). There should be continuity, which would indicate the ICU may not be the issue. (#4 is to check the exit of the ground from the ICU (passed through).) Nothing has to be turned on with this test, only the driver's door opened.
To test for continuity, set the multimeter to either the "ohms" or the setting it will beep when you hold the two leads together.
• If your meter beeps, it means you have continuity.
• If it is on ohms scale, you will have continuity when it reads close to 0 ohms.
• If it doesn't beep , shows OL (open line) or a 1 (infinity ohms); it means you don't have continuity.
#5: If the test in #4 shows continuity, there is no need for the #5 test. This test is see if the ground is present at the ICU. (#5 is to check that the ground from the driver's door switch is directly entering the ICU.)
#2: with everything plugged back in, if the headlight reminder chime or key-in chime works, the ground from the driver's door switch went through to the ICU.
#4: With the driver's door open, ground (-) should go from the door switch to the ICU. This test at Connector C602 is at the Grn/Orn wire after it passed through the ICU. You touch one of the ohmmeter's lead to the Grn/Orn wire terminal here and other other ohmmeter's lead to body ground (such as a ground bolt or bracket). There should be continuity, which would indicate the ICU may not be the issue. (#4 is to check the exit of the ground from the ICU (passed through).) Nothing has to be turned on with this test, only the driver's door opened.
To test for continuity, set the multimeter to either the "ohms" or the setting it will beep when you hold the two leads together.
• If your meter beeps, it means you have continuity.
• If it is on ohms scale, you will have continuity when it reads close to 0 ohms.
• If it doesn't beep , shows OL (open line) or a 1 (infinity ohms); it means you don't have continuity.
#5: If the test in #4 shows continuity, there is no need for the #5 test. This test is see if the ground is present at the ICU. (#5 is to check that the ground from the driver's door switch is directly entering the ICU.)
So I did a quick functionality test and the headlight reminder (key removed, headlights or parking lights on) and I do get the reminder. Likewise, with the key in the ignition, opening the door results in the reminder chime. The driver's side window delay cancel function also works fine.
I'm thinking that the ICU must be intact, which is consistent with the no visible damage to the ICU module.
I will verify the ground out in the morning and if that is as it should be, I will remove the instrument cluster and start inspecting it for damage. I will post the results sometime tomorrow.
I was able to confirm the ground presence at the output of the ICU on pin 7 of C602, so I proceeded to remove the instrument cluster.
Here's the before shot showing the fried etch coming off of pin 5 of the B instrument connector.
Damaged etch on instrument cluster circuit board.
So I repaired the damage by soldering in a 24 gauge wire over the damaged area as shown.
Repaired etch
All is much better now! Of course that flaky lamp went completely out and it's one of those with a blue rubber "condom" over the light bulb that was baked on and impossible to remove without destroying it, so now I'm waiting on a replacement set of blue LED bulbs to replace all 4 of them...lol.
I want to give a huge shout out / thank you to tech8 for all the outstanding and detailed help in running down the problem.
The problem was where I suspected it would be, but I now know a lot more about the functions of the Integrated Control Unit! I had never thought about the warning chimes for the key left inserted, lights still on with key removed/driver's side door opened and the "kill" function of the power windows operation after the driver's door is opened.
I will mention that as I expected, ohm checking for continuity with the electrical system is problematic.
With the driver's door open, pin 7 of the ICU connector C602 is near 0 volts, and goes to 12 volts with the door closed. This makes taking a continuity check to the chassis a bit problematic, but it was not a real issue. I only mention it in case someone inexperienced happens to follow this thread with a similar problem.
05-09-2015, 05:41 PM
Need wiring help 94 Accord LX
Re: Need wiring help 94 Accord LX
