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Old 11-04-2020, 06:32 AM
jerome951 jerome951 is offline
 
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Default Relay understanding help

Hi All,
Trying to troubleshoot my non-functioning ABS system. System doesn't work but no dash warning light. Pump also doesn't pressurize itself when first taking off.

Below is a picture of the relay which powers the ABS computer (and I think the pump as well)
Am I correct in interpreting the relay diagram as follows:

pin 31 - incoming switched power (from ignition, in this case)
pin 15 - ground for switched power
pin 30 - power from battery
pin 87 - power out to ABS computer

Thanks for clarifying...
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Old 11-04-2020, 08:37 AM
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That's how I would interpret it.

ed
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Old 11-04-2020, 02:22 PM
matt de maria matt de maria is offline
 
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30 is battery power.
31 is ground
15 is keyed power
87 is output of relay (from 30)
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Old 11-04-2020, 03:11 PM
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That's how I would interpret it
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Old 11-04-2020, 04:23 PM
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Old 11-04-2020, 05:40 PM
jerome951 jerome951 is offline
 
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Thanks All, especially Matt.

I did some quick testing and the relay appears to be working on the bench, so I'll have to dig elsewhere.
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Old 11-10-2020, 12:23 PM
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Relays die for three main reasons:
1) the solenoid opens or shorts and doesn't provide the electromotive force to pull the contact arm down. Easy to diagnose and fix.
2) corrosion on the pins and receptacles that will insulate the electric current and voltage. Easy to see and fix.
3) the more sinister and frustrating reason is the mechanical contact pads start to wear and can start to have pitting and cause arcing. These mini arcs can accelerate the degrading of a smooth contact between the two surfaces and build up carbon and crud which will insulate the contacts to some degree. In this case the relay may do really funky things. May work initially and then not...may lower the voltage to the intended recipient and it doesn't work properly, may fuse together and never turn off the voltage to the recipient, etc. You can take them apart and inspect the contact surfaces. If any blackish residue on them it can be cleaned off and it may be healthy for a while...but we're talking brakes here. One of my old electronics teachers told me a long time ago that once the contact surfaces degrade, they continue to reap havoc as the arcing will come back and eventually the relay will fail.
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