Daytime Running Lights (DRL) Diode Bypass?? - Chevy Impala SS Forum
 
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post #1 of 8 (permalink) Old 08-26-2017, 07:40 AM Thread Starter
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Daytime Running Lights (DRL) Diode Bypass??

Hello All,

My DRL system is causing the headlights to flicker. At the moment I have disconnected the DRL Module behind the front passenger kick panel.

I was wondering if anyone removed the DRL Diode (located above the brake pedal, next to the steering column - look for a large finned heat sink) and inserted a jumper wire in the connector? This would provide 12V to the headlights instead of ~10V. In theory this would work?

Looking forward to your feedback.

Thank you and take care,
PK
1996 Impala SS (102K km - for sale as of May 2018), 1994 Ford Escort, 1981 Mercedes 300SD (SOLD), 1971 VW Beetle Convertible (next project).
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post #2 of 8 (permalink) Old 08-26-2017, 10:19 AM
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I have not tried to removed the DRL Diode. Removing it will increase the current through the DRL module and it might fail.

I do not think you have supplied enough information.

If you have a stock headlight setup you have some electrical issues. Maybe a failed diode in the alternator.

If you have installed HD headlights supplying them with another power source through a relay would work.

Z09B4U
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post #3 of 8 (permalink) Old 08-26-2017, 03:56 PM Thread Starter
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Hello Z09B4U,

Many thanks for the prompt reply.

Headlights (low/high + all exterior lights), work fine via the switch on the dash (I don't have the TS option). So I know it is either the DRL Diode of DRL Module (currently unplugged). Failure happened yesterday and due to schedule I have not been able to trouble shoot other than than determining it is related to the DRL circuit. I have checked battery voltage; not running ~12.5V, engine running between ~13.8 and 14.3V.

Initial symptoms were as follows; driving in stop/go traffic yesterday with air on I noticed that the fan speed was cycling ever so slightly and the clock display has flicking in unison (about every few seconds). We were headed for a restaurant at about 20:00 with night falling when I noticed that I had not DRL headlights. Pulled into a parking lot and noticed the flickering - DRL headlights were trying to come on. Driving over bumps caused them to flicker on and off.

Since we had a 1.5 hour drive home a little trial and error proved that we could switch on all exterior lights except the low beams via the dash switch. Clicking on the high beams gave us headlights. Fortunately I had a few basic tools in the trunk so I adjusted the headlights to approximate the low beam pattern and drove home without incident. BTW switching off the high beams resulted in no lights.

A quick review of the wiring diagram revealed that I couldn't disable the DRL system via the two fuses so I popped the passenger kick panel and unplugged the DRL Module. I'm currently using my parking lights as DRL.

Based on the above my assumption is the DRL Diode as that component is a current load based device.

I hope the above gives you sufficient info to work with.

We have family visiting so I won't be able to do any proper trouble shooting until Tue or Wed of next week.

BTW, where in Canada do you live? PM me if you would rather keep this private. I'm in LaHave, NS.

Thank you and take care,
PK
1996 Impala SS (102K km - for sale as of May 2018), 1994 Ford Escort, 1981 Mercedes 300SD (SOLD), 1971 VW Beetle Convertible (next project).
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post #4 of 8 (permalink) Old 08-26-2017, 04:47 PM Thread Starter
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Hello Z09B4U,

Forgot three points; headlights are stock with slightly better output bulbs, wiring harness/relays, etc. is original and car has 100K km on the odometer. I don't think the latter has any bearing on the situation.

Hope it helps.

Thank you and take care,
PK
1996 Impala SS (102K km - for sale as of May 2018), 1994 Ford Escort, 1981 Mercedes 300SD (SOLD), 1971 VW Beetle Convertible (next project).
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post #5 of 8 (permalink) Old 08-26-2017, 08:32 PM
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My experience and the circuit diagrams suggest that the headlights should work normally with the DRL module unplugged.

Check your PM.

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post #6 of 8 (permalink) Old 08-27-2017, 07:24 PM
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post #7 of 8 (permalink) Old 09-02-2017, 03:46 PM Thread Starter
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Hello All,

Just wanted to update all of you on the DRL issue.

First, special thanks to Z09B4U for the troubleshooting tips.

To recap the initial problem, I noticed that my HVAC fan speed was cycling ever so slightly in stop and go traffic and the stereo display was flickering in unison. Shortly afterwards the DRL stopped working and headlights would only work on high beams (parking lights were OK).

Trouble shooting had me running around in circles until I discovered a high resistance ground on the negative battery terminal cable. Cleaning this up had the DRL and headlights/parking lights functioning normally. To be safe I ran an alternator output test by switching on all the lights (incl. high beams), AC on high, foot on the brake, power antenna operating and power seat operating. Voltage at the battery never dropped below 13.65V.

To reduce the load on the headlight switch and the DRL Module I modified the circuit to uses relays (30A each). One for the DRLs and the other for the Headlights. The existing DRL and Headlight circuits trigger the relay coil (terminal 85 and 86). The power circuit for each relay (terminal 30 to 78) draws its power from the headlight fusible link (before the headlight switch). I know, it is a pain to replace if the fusible link blows - I have a circuit breaker that I can substitute when the time comes. Please note, I have bypassed the DRL Diode so the headlights receive the full 12V when the car is running and not the normal 10V. Now the headlights are a little brighter during the DRL operation.

The DRL and headlights work to my satisfaction. :-)

Hope it helps.

Thank you and take care,
PK
1996 Impala SS (102K km - for sale as of May 2018), 1994 Ford Escort, 1981 Mercedes 300SD (SOLD), 1971 VW Beetle Convertible (next project).
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post #8 of 8 (permalink) Old 09-02-2017, 04:08 PM
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You saw the light.......

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93 9C1: Work & Cubic Ca$h This started with a new headlight and fender Celeritas In Conficiendo
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