Troubleshooting Voltage Drop Across Relay

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Khombo

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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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What is the voltage between Pins 30 and 87 when you have the 4v?

You have a voltage drop across some point in the circuit; you have to narrow it down.
 
LarryFine said:
What is the voltage between Pins 30 and 87 when you have the 4v?

You have a voltage drop across some point in the circuit; you have to narrow it down.
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4v is the voltage that I am receiving from pins 30 to 87 when the vehicle is in run or start.
 
Khombo said:
4v is the voltage that I am receiving from pins 30 to 87 when the vehicle is in run or start.
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I thought you were reading 4v to ground on Pin 87. So you're reading (13.6 - 4) 9.6v from Pin 87 to ground?

At any moment, the voltage that you're reading between Pin 30 and Pin 87, and that between Pin 87 and ground, have to add up to the voltage you're reading between Pin 30 and ground.

You can measure voltages between various points and Batt + as well as between various points and ground.
 
sorry i just went back out there and re measured. I am receiving the 12-13v while in run/start on pin 30 and i am receiving 0v from pin 87 to ground on multiple points.
 
So, you should be reading full voltage from Pin 30 to Pin 87 with the key on.

It's gotta be either the relay itself or one of the connections to Pin 30 or Pin 87.

A temporary jumper between those two socket slots should make the DRLs come on.

Voltage is being dropped across a point where it shouldn't be; you need to find that point.
 
Just to clarify I am not receiving the 12-13v from pin 30 to 87 with the key on. I have swapped multiple relays inside 6 to be exact. I have also tested 4 relays using a power supply and adding power across pins 86 and 30 and took readings of the voltage on just the relay itself and they were functioning properly. I just dont know the next step in trying to pin point where the voltage is dropping.
 
Don't overlook the relay socket/base. Volvo's were famous for burning them up. Also, don't overlook the ground side after the lights.

Typically you can pull the relay, crimp a couple of terminals on 6" of #12 wire, and plug the jumper into relay socket.
 
I have a 2001 silverado. I think I am going to add a jumper wire across pins 30 and pins 87 with a 10a fuse inline and tie a rocker switch inline after the fuse.
 
The body control module at the lower left in the schematic has to pull pin 85 to ground to activate the relay. Does the voltage at pin 85 go close to zero?
 
It is a common problem. The sockets for the DRL bulbs burn up a lot. Ambient light sensors are another possibility. Sometimes operator error; not knowing you have to be in drive, not having headlight switch in auto. Not a GM/Chevy guy anymore but some of them had a diode that could be your problem as well.
 
Russs57 said:
It is a common problem. The sockets for the DRL bulbs burn up a lot. Ambient light sensors are another possibility. Sometimes operator error; not knowing you have to be in drive, not having headlight switch in auto. Not a GM/Chevy guy anymore but some of them had a diode that could be your problem as well.
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So far I have replaced the fuse block to include the fuses and relays, I have replaced the sockets, ambient light sensor and my truck model doesnt have a diode like the older models. I am also doing all the troubleshooting with the truck in the auto with the tires blocked and the vehicle in drive.
 
synchro said:
The body control module at the lower left in the schematic has to pull pin 85 to ground to activate the relay. Does the voltage at pin 85 go close to zero?
Click to expand...


from what I measured yesterday while in run/start I was getting 12-13V. I can go back out there and check again.
 
Going back to OP:
Khombo said:
. 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.
Click to expand...

You should not have had 13.6 V (presuming to ground) on both coil terminals, but rather should have had voltage across them. You need nominal 12 volts to pull the relay in and close the output contacts. Same volts to ground on both those terminals means there is no volts across them
 
GoldDigger said:
So was it a bad interconnection or a fault in the control module?

Sent from my XT1585 using Tapatalk
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To be honest i Just took a resistance measurment and was reading around 800 ohms so I tapped into the output of pin 85 to the control module and tied a 3 way splice back to chassis ground
 
Khombo said:
To be honest i Just took a resistance measurment and was reading around 800 ohms so I tapped into the output of pin 85 to the control module and tied a 3 way splice back to chassis ground
Click to expand...

That may not be a good solution if pin 85 of the control module is an output intended to be able to inhibit the DRL system!!!!!
As it stands now there may be a problem with the wire (fine, patch around the wire), or with the control module (1. Module is bad - replace or kludge, or 2. module has what it thinks is a good reason for not enabling the DRL - troubleshoot or ignore and hope there are no other bad effects.)
 
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