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Old 04-05-2019, 12:19 AM   #1
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Parking brake light always on (but not really)

Hi all,

I have this strange problem with the parking brake light in my dash (2006 ZX3). The light is always glowing, but not at full brightness, maybe at 20% (though today it started flickering between maybe 20% and 50%). And I mean always, even when the ignition is turned off and the key is out of the ignition. It comes on properly for a few seconds when I turn on the ignition (as expected), the goes back to 20%. It comes on and stays on fully when I engage the parking break (while the ignition is on). I checked the fluid levels and they seem fine. I disconnected the wiring from the brake fluid sensor (at the reservoir cap), but the light keeps glowing. Any idea what this could be? Given that it continues even after the ignition is turned off I don't think it's either of the switches (fluid level, parking brake). Thoughts?

Thanks!
T.


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Old 04-06-2019, 08:17 PM   #2
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Originally Posted by ZeeGerman View Post
Hi all,

I have this strange problem with the parking brake light in my dash (2006 ZX3). The light is always glowing, but not at full brightness, maybe at 20% (though today it started flickering between maybe 20% and 50%). And I mean always, even when the ignition is turned off and the key is out of the ignition. It comes on properly for a few seconds when I turn on the ignition (as expected), the goes back to 20%. It comes on and stays on fully when I engage the parking break (while the ignition is on). I checked the fluid levels and they seem fine. I disconnected the wiring from the brake fluid sensor (at the reservoir cap), but the light keeps glowing. Any idea what this could be? Given that it continues even after the ignition is turned off I don't think it's either of the switches (fluid level, parking brake). Thoughts?

Thanks!
T.
Basically when the ignition is on vehicle power (VPWR) is supplied to one side of the brake warning light thru a microprocessor in the instrument cluster (IC). The other side of the light/microprocessor is wired to the parking brake switch and the low level switch in the MC reservoir. When either switch closes the light/microprocessor is connected to ground. The only other path would be through a ground fault in the IC/microprocessor. Based on the symptoms you describe - especially the dim light - I would highly suspect a internal problem in the IC/microprocessor. Do you have a tach or non-tach cluster?

You can try bench testing the IC to verify that the ground is not from either switch. I will post the schematic later.

Paul
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Old 04-06-2019, 11:00 PM   #3
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2005 instrument cluster and connector schematic

Paul
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Parking brake light always on (but not really)-2005-instrument-cluster-1.jpg  

Parking brake light always on (but not really)-2005-c2220.jpg  

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Old 04-08-2019, 01:11 AM   #4
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Hi Paul,

Thanks for your response, that helps a lot. I guess it's time to take a closer look at the IC. Looks like taking it out isn't too complicated. If it turns out to be ground fault in the IC, is there an easy (read: non-destructive) way to open it up and take a closer look at the circuit board or is it a sealed unit? This is the IC with a tach.

Thanks!
T.
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Old 04-08-2019, 01:19 AM   #5
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Also, just to double check, if I remove the IC and supply 12V to pin 28, ground to pin 30, it should start glowing if it's a ground fault in the IC, right?
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Old 04-08-2019, 08:16 AM   #6
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Quote:
Originally Posted by ZeeGerman View Post
Also, just to double check, if I remove the IC and supply 12V to pin 28, ground to pin 30, it should start glowing if it's a ground fault in the IC, right?
I think you need to supply 12 VDC to pins 6, 12, and 28 then try grounding at 20, 22, and 30 -individually- and see if you can get the light to glow dimly (it should glow bright with 20 or 22 grounded). If it glows dimly when grounded at pin 30 I think that would indicate an internal fault.

Ive replaced but not opened up these ICs so Im not sure what you will find inside. Im sure if you search the internet you will find some info on disassembly, etc.

Good luck
Paul
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