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Old 10-27-2012, 07:58 PM   #1 (permalink)
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03 MDX key wont turn off engine if lights are on

An interesting problem just popped up on our 2003 MDX base model (not touring) - non-nav.

If the MDX is running and you turn the key to the off position, while the headlights are on (parking lights, on or auto), the engine will not shut off.
It seems like everything else happens that you would normally expect when you turn off the key - the climate control system turns off, the big info display (mpg, time, etc) shuts off, the interior lights come on, the tach drops to 0, etc.
If you then turn off the headlights, the engine will shut off. very strange...

If you turn off the ignition with the headlights in the "off" position, the engine shuts off in a normal fashion.

Other notes
- even if the headlights are off, the headlight indicator light on the dash is lit (as if the lights are on).
- if you have the key out, headlights on, engine running, occasionally, the odometer will flash and the tach needle with jump a little.

I was thinking this might be a faulty ignition switch, but the whole headlight thing has me very confused.

Has anyone encountered this before? any ideas on what to check/fix?

Thanks
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Old 10-28-2012, 11:25 AM   #2 (permalink)
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There is an ignition coil relay that is always hot and energizes the COP's for each cylinder. Hard to believe it's not switched, but that is what the circuit diagram shows. Sparks are actuated by ECM supplying ground path at correct time to send spark to the plugs. For some reason your ECM is continuing to run the engine; supplying both fuel pressure and ignition.

Why, a faulty ignition switch seems most likely. Keyswitch is remaining partially on. This doesn't work w/ other parts going off, but there are multiple ganged switches in the ignition switch assy, and perhaps one set drives the ECM.

Other Honda/Acura products have trouble w/ worn ignition switches so maybe MDX's also. Check DIY section for further guidance on replacing the ignition switch assy. It's an easy diy on most honda/acura products.

good luck
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Old 10-28-2012, 07:25 PM   #3 (permalink)
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Thanks - I'll start searching the forums for the process to replace the ignition switch.

Just to make sure we are talking (typing?) about the same thing, is this the correct switch assembly (reference #8 in the diagram)? SWITCH, STEERING: Discount Honda and Acura parts and accessories - OEM Acura Parts
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Old 10-29-2012, 06:53 AM   #4 (permalink)
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Yes, that is the ignition switch assembly.

good luck
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Old 11-07-2012, 09:30 PM   #5 (permalink)
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We haven't replaced the ignition switch yet (just going through the shop manual now)
but we now have some interesting new new behaviors

If the car is running, with the lights on and you turn off the ignition and remove the key (but leave the headlights "on") the engine continues to run as before, but all accessories are turned off just as if you had removed the key.
If you then step hard on the brake pedal (or turn off the lights), the engine will stop.

We now suspect that it's something like a relay that's getting stuck on - keeping the engine running, and the extra load of pressing the brakes, or the chnage from shutting off the lights is just enough to cause the relay to release - and stop the engine. Just guessing here.

oh, and just to add to the fun, now the dashboard lights (background lighting, warning lights, etc) periodically blink when the ignition is in the on position - before the car is started.

My daughter has now named the mdx "Christine"....
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Old 11-15-2012, 02:33 AM   #6 (permalink)
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I have the same problem with my 03 MDX Touring. I turn the key to the "off" position and the engine continues to run. I turn the lights from "auto" to "off" and lo and behold the engine shuts down. It is the craziest thing.

I took it to my mechanic and he "ran some tests", $400 later I still have the problem.

So did replacing the ignition switch solve your problem?
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Old 11-15-2012, 09:08 PM   #7 (permalink)
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do you have remote start on it? (perhaps original owner installed it but never gave you the remote for it or never told you?)

may i recommend ohm-ing out the ignition switch before replacing it?
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Old 11-24-2012, 02:54 AM   #8 (permalink)
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It doesn't have a remote start. I'll have suggest to the mechanic to ohm out the ignition switch before replacing.
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Old 11-25-2012, 12:19 PM   #9 (permalink)
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I'm sorry for the delay in responding, I got sidetracked by the holidays
.
I'm working on the ignition switch replacement right now.
On a positive note, I didn't need to chisel out any bolts to get the switch replaced - it was just 2 Philips head screws - once I got the top and bottom plastic steering column covers off.

On a negative note, I can't see where the new ignition switch plugs into. It looks like it might be behind the fuse box - I'm not looking forward to pulling that mess out.

I've been searching the forums to find a description of how to do this, but, so far - I've come up empty. I'll try to post the procedure if/when I get this finished.
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Old 11-25-2012, 02:23 PM   #10 (permalink)
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I just finished installing the replacement ignition switch and putting all the pieces back together.
The MDX seems to be running better, but I'll have to report back in a week or so, as the problems were intermittent.

A few notes on replacing the ignition switch
0. Definitely disconnect the battery before starting this process.
1. Remove the Instrument panel trim first - it's only 2 screws and a few wiring harness plugs and makes it a lot easier to get out the bottom and top halves of the steering column covers
2. If you are just replacing the electrical switch and not the key lock, you'll only need to remove 2 screws on the back of the existing electrical switch to remove it. You do NOT need to remove the whole ignition assembly.
3. You will need to remove the lower dashboard side cover and lower dashboard cover
4. I removed the lower kick panel cover - the one that has the cutout for the hood release. I'm not sure how much it helped, but it didn't hurt to remove it.
5. The ignition switch harness plug into the back of the fusebox, you will need to move the one nut that holds in the fusebox (the one by the brake pedal). and try to gently push the fusebox out an inch or two (you wont get much more slack in the cables) to remove/insert the harness plug. This is the most painful part of the whole process - took me over an hour to get it right.
6. As long as I was messing around with removing dash panels - it seemed like a good time to replace the broken air vents. Got those from the same place that I had ordered the ignition switch from.
7. I did think about running through the tests in the service manual to test the ignition switch before replacing it - but with an intermittent problem like this, it could test fine now and still be broken tomorrow. In the end, I decided that, as long as I had to take things apart, I might as well replace the switch.
8. The official Acura Service Manual was mostly useless in this process - the diagrams didn't show much and the procedure for replacing the switch mentioned nothing about having to get to the back of the fuse box.
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Old 12-01-2012, 09:34 AM   #11 (permalink)
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The problem is back - so replacing the ignition switch didn't help (or maybe it didn't solve the whole problem - who knows?)

To recap - if the MDX is running with the lights on, and you turn off and remove the key, the car engine continues to run and can only be turned off by turning off the lights.
When the keys are removed all accessories (radio, heater fan, dash lights, etc) shut off as expected, just not the engine.

One other symptom we've noticed: If the car is off, and you put the key in the ignition and turn the key to the "on" position, the parking lights will come on - even if the switch for the lights is set to off. Also at the same time, the indicator on the dash for lights on is lightly illuminated.

Maybe it's time to start replacing relays?
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Old 12-01-2012, 11:24 AM   #12 (permalink)
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Since the lights normally work with the car on or off, it seems the ignition wire is shorting with a light wire. Most likely with a parking light wire since your ignition will power the parking lights and the lights will power the ignition.

Before changing relays I would try to find out where those wires are in the same harness. Something might have gotten pinched.
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Old 12-01-2012, 01:21 PM   #13 (permalink)
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Have you tried replacing the ignition relay? See attached file image. I'm not sure this would cause the engine to run on by itself, even if shorted. ECM must still supply spark timing and fuel pump, and injector pulses, but maybe so.

tough problem! my condolences.

good luck
Attached Files
File Type: pdf MDX_IgnitionDiagram.pdf (78.3 KB, 43 views)
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Old 12-02-2012, 05:02 PM   #14 (permalink)
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I have not tried replacing the ignition relay - have to wait for parts to do that.

I just finished going through the test procedure for the automatic light control unit and it tested out fine.
I also ran through the procedure for testing the Combination Light Switch (the turn signal & headlight stalk) and that failed - but only when in "high beam" mode, and only with pin 2 not having continuity with any other pins. I believe that's the pin that is supposed to shut off the fog lights when you turn on your high beams. By the way, the fog lights work fine

One other note - If the key is in the on position and the combination light switch is disconnected then the headlights and the parking lights turn on - as soon as you plug back in the combo light switch, the headlights turn off (parking light stay on). Definitely something is shorting. Time to trace more circuits.

I've been looking for damaged wires too, but, so far, I haven't found anything
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Old 12-03-2012, 12:15 PM   #15 (permalink)
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I did swap the ignition coil relay with another relay that uses the same part - no change. So, it looks like that relay is still good.

I keep looking for frayed wires - no luck so far.

When I turn on the lights now (without the key in the ignition), the whole instrument console comes on, including the fuel gauge coming up to the proper level and all the warning lights going on. Note that the trip computer display (temp, mpg, time, etc), the radio, and the ac unit/fan do NOT come on without they key in the "On" position.

the replacement combo switch gets here in 2 days - maybe that will help?
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