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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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Old 07-05-2015, 05:21 PM
DHoang's Avatar
DHoang DHoang is online now
Location: Austin, Texas
Join Date: Dec 2008
Posts: 1,023
Mein Auto: '98 528i, '82 323i
1998 528i LCM 2 Repair Low light beam stuck on

I have an intermittent low beam lights & rr tail lights (L&R , Fr& rr) that's stuck on. Some days everything's fine, other days, those lights stay lit and in the process locks out other exterior light functions. When they're stuck "on", at least I can turn them off with the key switch. But when the problem occurs, the following don't work:
turn signals
hazard lights
hi beams
reverse lights
fog lights
brake lights
cruise control (was working fine right before)
rr window defroster (this hasnn't worked prior to this problem, btw)

The following still works:
ASC light
a/c & heating
dash/instrument light (fade down feature doesn't work)

The battery shows 12.5v when engine's not running, and 13.9v at idle.
There's no signs of water leaks by the LCM, and LCM circuit board & connectors shows no signs of corrosion.

So at this point, I'm going to go ahead and buy replacement mosfet chips and DIY.

Everything that's written about this repair points to the replacement of the VN750/BST426L1
mosfet chips that controls the HIGH BEAMS.

My question therefore is this:
Even though my problem is that of the LOW BEAMS being stuck "on", do I change out the VN750/BST426L1 chips b/c this is the weak link/source of the problem, or do I change out the chips that controls the LOW BEAMS (they're the BST432E2 Infineon)?
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Old 07-05-2015, 05:55 PM
edjack edjack is online now
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Location: San Jose, CA
Join Date: May 2007
Posts: 11,017
Mein Auto: '97 540i 6 speed
Your symptoms do not align with traditional ones. Typically, when the output transistor dies, the lights stay on, even with the ignition off, and can only be extinguished by disconnecting them. Your symptoms may indicate an intermittent failure of the logic on the PC board. This may require a replacement LKM. Perhaps someone else can step up on this.

I have the classical condition on my right high beam. I bought five transistors. When I received them, I could not believe how small they were! I don't have a soldering iron that small, nor nimble enough fingers, to replace them. I may have to farm out the repair.

The LKM must be coded.

Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

Last edited by edjack; 07-05-2015 at 05:56 PM.
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Old 07-06-2015, 05:37 AM
DHoang's Avatar
DHoang DHoang is online now
Location: Austin, Texas
Join Date: Dec 2008
Posts: 1,023
Mein Auto: '98 528i, '82 323i
If it's not the transistors, then I'll have to escalate it to the next level, and buy a new LCM/LKM.

Question, anyone here regret upgrading their existing LCM/LKM ver. 2 to the newer ver. 3?

I've seen a few posters say they buy the ver. 3 LCM OFF the X-5. Any reason not to get one off the '99-up e39 ones?
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