2013 Corolla washer pump not working

[Ting ting]

Hi guys, new to the club, hope can get some idea on my car please.

Washer pump not working and I did the follow test:

1. Pump is fine, test by a 12v direct to it and its work.

2.Swap a good pump but still not working.

3. The hardness has 12.5v power.

4.I thought it may be the hardness contact problem, so I but 2 wires directly from the harness to the pump, but the pump still not working.

5. Fuse is good.

Any idea will be appreciate ! Thank you.

Ting

[Woofwoof]

Perhaps test the relay?

[Ting ting]

Hi woofwoof,

Will the harness has 12v if the relay is bad? 

Ting

[Red_Corolla]

What kind of test instrument are you using and how are you connecting it?

I must warn you that you can never rely on a multimeter to test a power supply at an open plug. You have to connect a load to prove that the connections are good and the circuit is able to carry current. Either test using a bulb or keep the pump connected and test by back-probing.

[Ting ting]

Hi Red_Corolla,

thanks for the remind! I'll try to put it back and back-probing test it, but would you please explain why can't use a dmm on a open plug? Coz I can't find any explanation on the net. Thank you.

Ting

 

[Red_Corolla]

20 hours ago, Ting ting said:

Hi Red_Corolla,

thanks for the remind! I'll try to put it back and back-probing test it, but would you please explain why can't use a dmm on a open plug? Coz I can't find any explanation on the net. Thank you.

Ting

 

Sure, I can try. It is because a multimeter has very high internal resistance - usually 10Mohms when testing voltage. Basic electrical principals tell us that the part of the circuit with the largest resistance will have the highest voltage across it. Always remember this point, it is very important!

Just for example, let's say that you have a very bad connection somewhere in your washer pump circuit - something with 1000 ohms resistance. This will stop the washer pump from working for sure, but what will happen when you unplug it and complete the circuit using only your multimeter? You will still see 12v, because the resistance inside the multimeter is still many thousands of times bigger than this bad connection with 'only' 1000 ohms.  But if you were to use a small 12v test light that has a resistance of only about 100 ohms, then the voltage at the light would only be around 1v and you would know you are not getting power. The other 11v would be lost across the bad connection.

I hope that helps, it's simple electrical principles but difficult to explain very well without a diagram.

PS there are some multimeters that have a 'low impedance' mode where the internal resistance will be much lower to try and get around this issue.  But, for most multimeters, you can never rely on them to check power at an open plug. Always test with the real equipment connected.

[Ting ting]

Hi Red_Corolla,

You save me hours to understand this! Thanks so much!!