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Troubleshooting Voltage Drop Across Relay

Posted By: Khombo

Troubleshooting Voltage Drop Across Relay - 06/09/19 12:18 AM

I am currently troubleshooting my daytime running light circuit. I have provided a detailed diagram of the steps I have already taken to isolate my problem. As of right now I have verified power across my DRL Relay pins 86 and 85 (Hot in Run or Start), verified power from the relay to the body control module, verified power across DRL fuse 10A (Hot At All Times) and up to pin 30 (Common) on the DRL Relay. I have also verified continuity across Pins 30 (commmon) and 87a (NC) when vehicle is NOT in Run or Start. When the vehicle is in Run or Start I have approximately 13.6V on pins 30, 85 and 86; on pin 87 (NO) I am only receiving approximately 4V. I have verified 4 like relays with a 12V power supply and all the relays function properly and the single pole functions properly between the double throw.

I am looking for some explanation to why I am only receiving 4V across the relay while installed. I have verified the same relay with a 12V power supply to function properly.

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Posted By: JoeTestingEngr

Re: Troubleshooting Voltage Drop Across Relay - 06/09/19 02:16 AM

If you're stating that you are reading 4 volts across the common and N.O. contact, that would indicate that you have 2 or more times your meter's input resistance between the relay common and your chassis ground. Assuming a negative chassis ground, pull the relay and measure resistance between the N.O. contact and battery negative. Check the connection at the relay socket and the condition of the DRL ground connection.
Joe
Posted By: Khombo

Re: Troubleshooting Voltage Drop Across Relay - 06/09/19 03:01 AM

I went back outside a while ago and i must have taken a wrong measurement somewhere. I am receiving 12-13v on pin 30 (common) and 0v on pin 87 (NO). I am at a loss where to continue to troubleshoot after i have already verified 4 other relays to include the one I am using.
Posted By: gfretwell

Re: Troubleshooting Voltage Drop Across Relay - 06/09/19 03:49 PM

Measure the voltage between the common and N/O. With the relay energized that should be very close to zero (a very small fraction of a volt, ideally zero), With it open you should see the full voltage in the load circuit.
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