Relay testing for Novice Technicians

Hey, guys just question for the relay testing methods. Automotive relays draw approx 120-150mA current draw. Is it safe to jump terminal between 30 to 87 to check current draw on relays itself and say fuel pumps that would draw 3-5 amps of current draw?

It is one of those tests that is very easy to make a mistake on and short the wrong terminnals. I tend to use a test light first. You can buy sets of test by-pass relays that have a selection of relay units fitted with external switches but these are fairly expensive where I am so I have made a couple of home made ones from junkyard parts.

It is one of those tests that is very easy to make a mistake on and short the wrong terminnals.

Totally agree with Andy. Gotta be careful.

I've done it many times but if you're not sure don't do it.

This is a great video about troubleshooting a relay controlled circuit. Probably one of my favorite in recent history.
The 120ma current draw is just on the coil side of the relay, so jumping 30 and 87 would allow you to measure the current of the pump, not the relay itself.

That was a good refresher one Noah. Another that springs to mind was when Paul diagnosed the starter on his sons celica. He broke out the uactivate (spelling) relay bypass tool.

Yes, that's a handy tool. A bit pricey, but making relay testers from bit's of scrap takes some time and ingenuity. I've been considering abandoning my homemade ones for the U-Activate tester set.

Yeah I considered buying one. But like Noah says it's a bit pricey.
Also like the Power Probe as you can see in the video:

Sorry I didn't bother with the link. I'm on here on my phone normally.

One feature I liked about the look of the uactivate was the loop for an amp clamp. I don't have one though. Still looks cool.

I must confess I have unit for testing relays off car that I bought off eBay as an overstock/return item from Maplin (the UK equivalent of Radio Shack) for about 1/5 of the retail price. You connect it to the battery and plug a relay in, it cycles the relay 10 times and checks the coil and contact continuity. Of course it dosen't put the relay contacts under full working load curent.

www.maplin.co.uk/p/maplin-automotive-relay-tester-a19qx

Sorry I didn't bother with the link. I'm on here on my phone normally.

No problem Matt!

matt.white wrote: That was a good refresher one Noah. Another that springs to mind was when Paul diagnosed the starter on his sons celica. He broke out the uactivate (spelling) relay bypass tool.

I'd LOVE to have one of those. And one of the Smart BOBs , too

I've been getting by pretty well with this Lisle relay test set . Exactly like the ones featured in the Bad Engine Computer testing series. Very handy, but it's still possible to jump the wrong terminals if you're not careful.

These are what I use for current testing at the relay.

www.tooltopia.com/innovative-of-america-...NbHYiV8VPhoCAfvw_wcB


I use these at the fuse box:

www.amazon.com/307M-Fuse-Buddy-Mini-Curr...es+fuse+current+loop

www.amazon.com/308B-Fuse-Buddy-Current-L...es+fuse+current+loop

Tyler wrote:

I've been getting by pretty well with this Lisle relay test set.

Nice man. But still + $120

Why does everything have to be so expensive

I have the uActivate, it is kinda pricey. Haven't used it a lot yet but the times that I have, it's a pretty good tool. When I have the time, I'll run it through a bunch of tests and let you all know how it goes. But so far so good :woohoo:

I use this to test relays www.amazon.com/ESI-193-Black-Diagnostic-Relay/dp/B00NI10152

*shaka*

When I have the time, I'll run it through a bunch of tests and let you all know how it goes.

That would be cool. Nice link by the way, like that relay tester.....

Monde wrote: Hello
Does the pcm have anything to do in the starting system of this car? If the clutch switch when closed send a signal to the computer, there must be a reason for it, right?

Not sure what car you're referring to Monde :blink:
But, if the clutch switch is a PCM input, it's probably one of several inputs it must receive before the PCM will activate the starter relay.
I hope that's what you're asking about.

You mean the one I posted on page 2 here Monde?

The purpose of the clutch pedal switch circuit is for the PCM to monitor the position of the clutch pedal. This process is accomplished by reading the output voltage of the clutch position sensor. The clutch position sensor switch may vary in design from one vehicle to another, it is usually a basic "on/off" switch mounted near the clutch foot pedal on the support bracket. Regardless of the design, constant voltage is typically present on one side of the switch and the contacts are closed by engaging the clutch pedal transferring voltage to the starter or starter solenoid. This basic circuit and switch prevents starting the engine prior to engaging the clutch...