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how do you test a relay???

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relay test
15K views 6 replies 5 participants last post by  jasons 
#1 ·
Hi there all. I had my car diagnosed and it came up with fault p0480 ENGINE COOLANT BLOWER MOTOR 1 - CIRCUIT MALFUNCTION. I was told by another ao member that it could be a possible fault with the relay. can anyone help me pin point the relay and how to test if a relay is working or not. thanx
 
#4 ·
Hi!

To test a relay you first need to identified the coil and the contacts, It should be normally closed contacts an normally open contacts, when you apply voltage to the coil the opens ones must close and closed ones must open, if it doesn’t maybe the coil is open , you can check that with a Multimeter !
 
#5 ·
For a Bosch relay (as most are) the coil is between pins 85 (negative) and 86 (positive). The switched contacts are usually 30 (positive and 87 (and 87a), negative. Put a multimeter (set on resistance) or a circuit containing a battery and light bulb across the switch contacts and put 12V across the coil contacts. If it's working, the resistance should go from open circuit to zero, or the light should come on. Be very careful not to short anything. If you're using your car battery as the 12V source, a short will cause a really big bang.
 
#7 ·
if the relays have been removed or fuse changed at any point it will throw up a fault code.
Your relay may be perfectly fine.
Clear codes and monitor.
If you remove the relay for testing it will throw up the fault code again, so when tested be sure to clear codes again.
 
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