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How do I tell if a relay is bad and how do I test it

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Most vehicles have multiple relays in the fuse box.Many are the same.If you want to check a relay,a quick way is to exchange it with a identical part number relay in your fuse box.Say you want to check the fuel pump relay and it's the same number as the horn relay.switch them and see if the horn blows,if it does then the relay is good.

Posted on May 08, 2017


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Is there a way to tell or checkl if the main relay is bad on your vehicle

If it does not work then it might be bad. If you energize the coil and it does not actuate and close the switch, I'd say it is probably bad.

Jan 24, 2017 | Cars & Trucks

1 Answer

How can you tell if you're fuelpump or relay is bad on a 93 chev cavalier

easiest is chevy pumps hum and relays click so turn key on and listen should hear click and then a slight hum when pressuring up --no click can mean relay bad or over heated but tech way is remove relay and test with a meter or use another [same number relay]matching relay and turn key and if starts relay bad no start check the pump for power possible bad harness wire or connection or pump bad

Aug 11, 2016 | Cars & Trucks

1 Answer

Can i bypass the fuel pump relay on my 1989gmc s15 and get my truck to start

if the relay is bad yes.

If the problem is not the relay it won't help.

If it is the factory relay it will have a schematic on it to tell you what wires to jumper for testing

Apr 14, 2015 | GMC S-15 Cars & Trucks

1 Answer

How can you tell if fuel pump relay is bad

Take it out & test it

Lots to learn on the internet &
You Tube Video-- about relays

They can be tested in the car or switched
with similar one

Doubt it is bad

Oct 03, 2014 | Cars & Trucks

1 Answer

1996 jeep cherokee mil code 36

which engine, why not post engine your fixing.??????
chapter emissions...... cht.25
see that? then go to 36 code
page 3.
oxy 1/2 heater relay problem.
then page 19 explains the tests.
1/2 means the down stream 02
and the PCM tests the relay.
and fails.
so a fuse is blown or the relay is bad. is my guess.
fuse 10 or 17?
on car i dont guess, test the relay in place.
the Fsm does not tell you , how this is checked.
does the PCM monitor the coil pin, or the output pin of the relay.
wiring page 135 (pdf page) shows the wiring
my guess is the PCM watches the relay coil, and if not 12vdc
disabled. the coil is open or fuse blow, or as is true ,endlessly
wires bad, or bad connectors.

Aug 08, 2014 | Jeep Cherokee Cars & Trucks

1 Answer

How to tell when fan relay is bad

Need a test light and the wiring schematic. Should have power and ground to the relay. Also need a "trigger" wire which activates relay to allow power to flow out and to the fan.

Apr 05, 2014 | Scion xB Cars & Trucks

1 Answer

Car horn not working

as with all elect. fails check all fuses
in this case the 15 amp fuse marked, HORN
can i presume all else works good> car drives.?
all answers, USA spec car. nobody ever tells location, so..... if not USA< all answers wrong. the usa car has just 1 horn.....
got voltage to horn? 12v
Yes or no.?
if yes horn bad.
got voltage from horn relay
yes, bad wires.from, relay to horn
no, got voltage 12v to horn relay coil,
yes, good, no bad fuse.
got 0v to other relay coil (all tests honking)
yes, bad relay.
no, bad horns switch.

if you want me to guess. sure.
1: bad wires ../connections, end to end.
2 bad horn
3: bad relay
4: bad horn switch.

Dec 27, 2013 | 2005 Toyota ECHO

1 Answer

How do tell your relay is bad

Knowing the type of relay & how to test it

Without wiring daigrams,your done before you start

If you remove it from the car & can read & understand
any picture on the top of it,you can test out of the car

That is a job for a repair shop

Jun 09, 2012 | 2001 Ford Taurus

1 Answer

Get a code p1320 have changed coils plugs checked all grounds from ecm and chassis and all wires from ecm to coils only thing left from what i can tell is condensor if im missing any thing please help

I have seen through experience and not just from hearing that it was a bad crankshaft position sensor even without a DTC of P0335. Also a bad ECM relay has caused this. Yes I know if the relay is bad it's bad but have seen it. Below are the testing procedures to test the condensor and the relay. If these test out good I would go to the crankshaft position sensor but before you start buying anymore parts find the problem then fix it. If you need anymore testing procedures feel free to email me at and I will be happy to help. Now you're positive you have checked all grounds and any open circuits ? This is the most common cause that's why I ask. I hope this helps and good luck.



Nov 03, 2011 | 2000 Nissan Maxima

1 Answer

1994 astro van wont start seems like no fuel,how to test fuelpump?

If you don't have fuel pressure test equipment then try spraying engine starting fluid in the air cleaner if it starts then you probably have a bad fuel pump, fuse or relay. The easiest is to check all your fuses if they look good. Look for the relay center under the hood the cover to the relay center will tell you which relay is the fuel pump relay. Try swapping relays with one that looks the same in the relay center. If it starts after swapping relays then you have a bad relay. Hope this helps you :)

Dec 17, 2010 | Chevrolet Astro Cars & Trucks

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