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Ok, I had about my favorite problem to date with a Sport Sedan at the shop yesterday, and want to bounce some ideas around.
It's an '04 Aero sedan with automatic trans.
Since the customer bought the car 3-4 years ago he said the fog lamps never worked.
He munched the front a little bit, and had some body work done about 2 weeks ago, and along with bumper and lip the body shop installed two new fog lamps. All the wiring was intact.
The passenger side lamp was always lit starting at key-on. Lamp did not respond to fog lamp switch or activation in Tech2 menu (on or off, it always just stayed lit).
The driver's side lamp (the weird one) would light at key-on, but would shut itself off after 30-90 seconds after turning on. The driver's side also did not respond to switch, or to activation in Tech2.
In the Tech2 read-values menu the switch and power leads to the lights responded as expected (press button, press is detected, lamps change from Off --> On, indicator on dash lights and goes out normally), but the lights did not change to reflect it.
(BACKGROUND: the fogs are powered through the UEC, and triggered by signal from BCM hooked to the switch. The lamps are not supplied steady DC voltage, they are fed a variable AC signal that's pulse-width-modulate within UEC to keep the voltage at the bulb a steady +13V, regardless of system voltage or alternator charging voltage [system description claimed this was for temperature regulation in the lamp housing])
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At beginning of diagnostics there were codes stored for both lamps, C2525-04 (I think that was it) for 'Driver's front fog - open circuit' - the open circuit code was present for the other side too, don't remember the code ---- EVEN THOUGH BOTH BULBS WERE LIGHTING.
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Since the lamps are lighting, and since they're being controlled on feedback from UEC the wiring to the lamps was fine (checked quickly, but didn't do continuity or short circuit tests, they seemed to be working, just not responding to signal from the I-bus correctly.
I jumped right to more electronic diagnostics.
Pulled driver's door jam fuse cover, found a few leads spliced into switched power fuses to power an aux. phone input that was installed before he bought the car, and never worked (Red light #1 goes off in my head)
I removed BCM, UEC, and AHL (car has Xenon 1's) and re-added them in BCM --> UEC --> AHL order - all programmed to be equpped 'WITH FOGLAMPS' -
---> NO CHANGE in lamp behavior.
--> Re-add all modules this time selecting 'WITHOUT FOGLAMPS' on module add ------
----> NO CHANGE IN LAMP BEHAVIOR!!! They continued doing what they were doing initially, pass lit always, drivers lights at start for ~1 minute, then goes out.
Then, I did SPS re-flash on BCM and then on UEC, re-added modules 'WITH FOGLAMPS' .....
-------> STILL no change in lamp behaviour.
Then I re-added the modules such that it allowed the day time running lamps to be switched off (Low beam in POS 2 ONLY) 'WITH FOGLAMPS,' which did cause the foglamps to go off when headlamps were switched off, and turn back on when switched on - but the lamps still did not respond to the foglamp switch.
I was quite stumped at this point, and customer was very understanding (he had just come in to see about getting the driver's lamp fixed - he didn't like how rediculous the car looked with only one lamp lit all the time).
I ended up just removing the bulbs for him and keeping them both off, since he said he didn't really care if they were there or not, and so I wouldn't charge him for any more diagnostics, just took the easy way out.
I concluded that the next step would be thorough continuity and short tests at the leads, then possibly substitution of UEC and BCM control modules from known working ones in the car, I suspect might be internal fault in the control modules themselves, but so far that's the only symptom showing up from it.
.........But that left me dreadfully curious
Have any of you guys seen anything like this, or have any input for what I could have checked next otherwise, or have any other ideas?
Best,
Drew
posted by 75.28.6...
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