Problem diagnosis game

[Byteme]

Diagnosis game.

Back in the day if a light didn't work the order of diagnosis was fuse - switch - wire, socket - bulb  Today's fully electronic integrated cars have killed that simplicity.

The MB CLK320 started having electrical problems.  To wit:

Ignition off, turn on lights. There is a large tubular black thing under the plastic engine cover on the air intake side that clicks when the lights are turned on. Followed by a faint buzz from the left bank of coils.

Turn on the lights and insert the key and it won't turn. Turn off the lights and it turns and the car starts normally.

If you leave the key in position 1 and turn on the lights the license plate lights come on faintly. If I then start the car the license plate lights go out.

The tell tail for the rear fog light, that little round orange light near the light switch, comes on anytime I turn on the lights, even if I do not pull the switch out to the second detent to turn the rear fog light on. With the ignition off the rear fog light lights up very faintly, start the car and it goes out when it should be on.

Leave the lights on after shutting the ignition off and the warning lights on the instrument display start flashing randomly, along with the climate control and radio displays. This is accompanied by lots of clicking in the dash like relays being activated. If I step on the brakes while this is going on all that flashing and clicking stops. Also if the trunk lid was open when this goes on the trunk light is flashing. If I pull out the trunk light switch plunger to shut off the light or push it in like the trunk lid has been closed the flashing and clicking stops.

Sometimes when I open the trunk with everything else off the trunk light pulsates and there is an irregular clicking from the area behind the trunk liner behind the CD changer. There are some electrical items back there but I have no idea what they are.

The reverse lights have quit.

If I turn the ignition to run and put on the turn signals I can remove the fuse that is suppose to feed the turn signals and the signals continue to function without the fuse being in it's slot.


I gave up and took the car to the dealer and let them sort out the problem.

Your job:  Guess what they found and fixed.

[shp4man]

Modern cars are controlled by a network of modules . One bad module or short in the circuit can affect the whole network.

[giant_mtb]

[Morris Minor]

Bad grounding strap somewhere? Or loose connection to one of the battery posts? Guessing something simple

[MX793]

Bad O2 sensor.

More seriously, probably the control module for your lights.

[MexicoCityM3]

Bad O2 sensor.

More seriously, probably the control module for your lights.

This. Or the harness/wiring going in/out of that module.

[Morris Minor]

Rodents nesting in the wiring

[shp4man]

Rodents nesting in the wiring

That's pretty common, actually.

[CaminoRacer]

Blinker fluid needs to be replaced

[Byteme]

Turns out it was a broken ground wire in the part of the harness that feeds the trunk lid lights.  The factory ground wire is made of a 3-4 thick strands covered with brown insulation instead of many, many thin strands so it's more prone to failure.  With the way the electronics on cars are interconnected today it's almost like something quits working and the other electronic parts go on a sympathy strike.  And the brake light switch was faulty, despite the brake lights still working.  And the dealer replaced a few bulbs they thought were suspect (cheap enough so I didn't object).

The cost was more than I was hoping and less than I expected.  I did ask for and the dealer gave me a discount.

[GoCougs]

I was gonna guess water in a connector or a fuse box, but a bad ground is sorta the same.

The cascading failures were likely the result of related systems' failure to interpret the consequences of the bad ground, so they just sorta end up guessing.

[Byteme]

Some pretty good guesses.  Anybody else have a stumper they want to offer?

[MexicoCityM3]

1M Misfiring on one cylinder

Plugs replaced - problem persisted
Coils swapped - problem persisted

Not obvious. Go.

[Byteme]

1M Misfiring on one cylinder

Plugs replaced - problem persisted
Coils swapped - problem persisted

Not obvious. Go.

Fuel, injector issue?

[Rupert]

Bad ground?

[shp4man]

Needs compression test.

[giant_mtb]

Bad turbo.

[Rich]

Bad engine

[CaminoRacer]

Needs compression test.

Hole in the piston

[CJ]

Hole in the piston

Crush it.

[MX793]

Ignition control module or wires between the ignition module and the coils?

[FoMoJo]

1M Misfiring on one cylinder

Plugs replaced - problem persisted
Coils swapped - problem persisted

Not obvious. Go.

Intermittent or not firing at all?  Coil swapped or replaced?

[Cookie Monster]

Fuel rail/fuel pump problems?

[Byteme]

1M Misfiring on one cylinder

Plugs replaced - problem persisted
Coils swapped - problem persisted

Not obvious. Go.

So tell us what it was.   

[MX793]

Here's a fun one:

I get the dash warning indicator that I have a light out.  Based on the rapid blinking of the internal indicator when using the right turn signal, it's a blinker.  Walk around the car and sure enough, the right rear blinker is out.  However, if the headlights (and tail lights) are off, it works fine.  Also works fine when I hit the hazards/4-ways (regardless of whether the headlights are on or off), so it's not the bulb.  It will also blink a few times when I first hit the indicator when the headlights are on (I counted between 4 and 6 flashes after some experimenting).  The right tail light is also partially out (the part that also serves as the turn signal), but like the blinker, it works initially and then goes out after some short period of time when I first hit the headlamp switch.  Anywhere from 2 seconds to maybe a minute.

I made sure all of the connectors at the lamp assembly were seated to rule out a spotty connection.  Didn't check the ground, though the fact that the blinker works fine under certain conditions (like when the hazards are on) leads me to believe it's not at the lamp assembly itself.  Bad control module, maybe?

Getting tired of the electrical "quirks" with this car.  Serves me right for buying a VW.  They apparently didn't quite fix their shit after the 4th gen reliability/quality disaster.  Local Mazda dealer has a low mileage Mazda2 for a pretty good price (less than I paid for this Jetta, and a stick shift to boot).  Tempted to dump this heap and pick that up.

[Eye of the Tiger]

I was just looking up the Mazda 2, only to find it is no longer in production.
If there was a lightly used manual around here, I would trade the Element for it.

[ifcar]

The Mazda2 is a fun little car. Go for it!

One warning, in case you didn't already notice and this matters to you: If it's a Mazda2 Sport, it doesn't have cruise control.

[Eye of the Tiger]

The Mazda2 is a fun little car. Go for it!

One warning, in case you didn't already notice and this matters to you: The Mazda2 Sport doesn't have cruise control.

If the car is throttle by wire, aftermarket cruise control systems are literally plug and play. If it is cable, it is more difficult, but not impossible.

[MX793]

The Mazda2 is a fun little car. Go for it!

One warning, in case you didn't already notice and this matters to you: If it's a Mazda2 Sport, it doesn't have cruise control.

Interesting.  This car is advertised as a "Sport" model, but there are cruise control buttons on the wheel.  Did they come with non-functional CC buttons on the steering wheel?  Or perhaps this one is actually a Touring model?

For a winter car that will mostly see short distance commuting 3-4 months (and maybe 2000 miles) per year, I don't really care that much about not having cruise.  I've been without cruise control before.  And if the roads are snowy, I won't use the cruise anyway.

[ifcar]

Interesting.  This car is advertised as a "Sport" model, but there are cruise control buttons on the wheel.  Did they come with non-functional CC buttons on the steering wheel?  Or perhaps this one is actually a Touring model?

For a winter car that will mostly see short distance commuting 3-4 months (and maybe 2000 miles) per year, I don't really care that much about not having cruise.  I've been without cruise control before.  And if the roads are snowy, I won't use the cruise anyway.

Either it's aftermarket or it's actually a Touring, I'm pretty sure. Tourings also have alloy wheels, foglights, and red piping on the seats.