How to check for Power or resistance???Need help

Myron · 11-09-2009, 08:39 AM

So im trying to find out if there is a short in my wiring, Especially to the ECT (the one next to the cold start injector) also known as the water Temp Sensor

How would i do that using a multimeter, would i check for ground or resistance or OHM's...Not too fimiliar with the electric side but need to learn..

thanx

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nv4runner · 11-09-2009, 09:03 AM

What kind of a multimeter do you have? If its analog (uses a needle) go get yourself a $25 digital multimeter from Walmart. The analog meters don't have enough internal resistance and can hurt computer circuits when looking for voltage.

With the digital meter set to ohms, Key off, and connector unplugged lightly touch one of the wire terminals with one test lead and touch the other to ground. Go through the wire side of the connector whenever possible to touch the metal terminal. This will prevent the terminals from being damaged. If there is a really low reading on your meter, then that is probably the ground side of the circuit. Repeat the same for the other wire, if it has two. If both the wires have a very low (0.00-about 2 ohms) readings between the sensor connector and ground then the power wire is shorted to ground somewhere. If one has a low reading and one has a high reading then your circuit is probably okay.

If you want to test for voltage at the power wire you need to switch your meter to volts on a scale that can handle at least 12 volts. This sensor usually uses 5 volts but you can never be too careful when it comes to testing computer circuits. With the sensor connector disconnected turn the key to the on position (engine off) and touch the red lead to your power wire terminal and the other to a good engine ground. You should get a voltage reading. If you aren't then try the other wire. If still no voltage then you have an break in your power wire. If you do get a voltage reading, then connect your meter to both terminals. The reading should be very similar to the first voltage reading you got. If it is significantly different then you may have a problem.

If I had a 22re I'd be able to test it and let you know what the results should look like. Hopefully someone else can tell you what they've found. Good luck!

Myron · 11-09-2009, 09:27 AM

I have a digital autometer..

http://www.hobby-hour.com/electronic...multimeter.gif

Myron · 11-09-2009, 10:48 AM

so there looks like there is power to the harness for the water temp sensor. I got a 5 volt reading and then about a 3.9 Ohms reading..but nothing at a zero..so i think its time to replace the water sensor. what you think?

nv4runner · 11-09-2009, 10:34 PM

I use the same multimeter, but plan on upgrading to a Fluke 88 V if I can save up the money. It could be the water temp sensor. What is it that makes suspect you have an ECT sensor problem? What is the truck doing or not doing? Its always possible that it could be something else. The resistance you found is probably the computer, as the computer reads a voltage drop to sense water temp.

Hadmatt54 · 11-16-2009, 03:26 PM

You probably got this fixed by now, but if you haven't the FSM lists the following resistance values for the Water Temp Sensor. Remember that the resistance varies according to temperature, that is how the computer knows what temperature your engine is currently operating at. The sensor has 5 vdc. fed to it and as the resistance of the sensor changes some or all of that voltage flows back to the computer.So in order to accurately measure the resistance of the sensor, you have to know the temperature of the coolant that the sensor is immersed in.
Resistance ranges from 0.1 KiloOhms at 248 Degrees F to 13-15 KiloOhms resistance at -20 degrees F. If you have a 180 degree thermostat installed resistance should be approx 0.3-0.4 Kohms. for a 190 degree thermostat resistance should be approx. 0.2 Kohms.
The problem with your cheap multimeters is many cannot measure mega or Kilo ohms, so if you are going to start troubleshooting modern auto electronics, the first step is to save up and purchase a good quality multimeter.
Hope this helps.

11-09-2009, 09:03 AM	#2 (permalink)
nv4runner Registered User Join Date: Dec 2007 Location: Reno, NV Posts: 202	What kind of a multimeter do you have? If its analog (uses a needle) go get yourself a $25 digital multimeter from Walmart. The analog meters don't have enough internal resistance and can hurt computer circuits when looking for voltage. With the digital meter set to ohms, Key off, and connector unplugged lightly touch one of the wire terminals with one test lead and touch the other to ground. Go through the wire side of the connector whenever possible to touch the metal terminal. This will prevent the terminals from being damaged. If there is a really low reading on your meter, then that is probably the ground side of the circuit. Repeat the same for the other wire, if it has two. If both the wires have a very low (0.00-about 2 ohms) readings between the sensor connector and ground then the power wire is shorted to ground somewhere. If one has a low reading and one has a high reading then your circuit is probably okay. If you want to test for voltage at the power wire you need to switch your meter to volts on a scale that can handle at least 12 volts. This sensor usually uses 5 volts but you can never be too careful when it comes to testing computer circuits. With the sensor connector disconnected turn the key to the on position (engine off) and touch the red lead to your power wire terminal and the other to a good engine ground. You should get a voltage reading. If you aren't then try the other wire. If still no voltage then you have an break in your power wire. If you do get a voltage reading, then connect your meter to both terminals. The reading should be very similar to the first voltage reading you got. If it is significantly different then you may have a problem. If I had a 22re I'd be able to test it and let you know what the results should look like. Hopefully someone else can tell you what they've found. Good luck! __________________ 92 4Runner 5 spd V6 31X10.5X15LT, Aisin Manual Locking Hubs, K&N FIPK, Converted HID Driving Lights, Fog Lights, Rear in Bumper Mini Flood Lights

11-09-2009, 09:27 AM	#3 (permalink)
Myron Registered User Join Date: Sep 2006 Location: Scottsdale,Arizona Posts: 191	I have a digital autometer.. http://www.hobby-hour.com/electronic...multimeter.gif __________________ 1987 Pick Up 2.4L 4x4 2004 Rallirt 2008 Taco

11-09-2009, 10:48 AM	#4 (permalink)
Myron Registered User Join Date: Sep 2006 Location: Scottsdale,Arizona Posts: 191	so there looks like there is power to the harness for the water temp sensor. I got a 5 volt reading and then about a 3.9 Ohms reading..but nothing at a zero..so i think its time to replace the water sensor. what you think? __________________ 1987 Pick Up 2.4L 4x4 2004 Rallirt 2008 Taco

11-09-2009, 10:34 PM	#5 (permalink)
nv4runner Registered User Join Date: Dec 2007 Location: Reno, NV Posts: 202	I use the same multimeter, but plan on upgrading to a Fluke 88 V if I can save up the money. It could be the water temp sensor. What is it that makes suspect you have an ECT sensor problem? What is the truck doing or not doing? Its always possible that it could be something else. The resistance you found is probably the computer, as the computer reads a voltage drop to sense water temp. __________________ 92 4Runner 5 spd V6 31X10.5X15LT, Aisin Manual Locking Hubs, K&N FIPK, Converted HID Driving Lights, Fog Lights, Rear in Bumper Mini Flood Lights

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11-16-2009, 03:26 PM	#6 (permalink)
Hadmatt54 Registered User Join Date: Oct 2005 Location: New Brunswick, Canada Posts: 23	You probably got this fixed by now, but if you haven't the FSM lists the following resistance values for the Water Temp Sensor. Remember that the resistance varies according to temperature, that is how the computer knows what temperature your engine is currently operating at. The sensor has 5 vdc. fed to it and as the resistance of the sensor changes some or all of that voltage flows back to the computer.So in order to accurately measure the resistance of the sensor, you have to know the temperature of the coolant that the sensor is immersed in. Resistance ranges from 0.1 KiloOhms at 248 Degrees F to 13-15 KiloOhms resistance at -20 degrees F. If you have a 180 degree thermostat installed resistance should be approx 0.3-0.4 Kohms. for a 190 degree thermostat resistance should be approx. 0.2 Kohms. The problem with your cheap multimeters is many cannot measure mega or Kilo ohms, so if you are going to start troubleshooting modern auto electronics, the first step is to save up and purchase a good quality multimeter. Hope this helps.