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Testing your car’s computer requires learning how to test ECU with multimeter.
Typically, you would use a scanner to test the computer.
But if you don’t have any of those fancy tools, you can use a digital or analog multimeter to find out if your ECU is working. Luckily, testing this unit does not take much time with a regular multimeter.
When testing the ECU, you might also have to check other sensors before assuming there’s something wrong with the computer. More on this down below.
What is an ECU?
ECU or ECM is short for Electronic Control Unit. This is a built-in computer that controls what’s going on in your engine. You could think of the ECU as the brain of your car.
For instance, the ECU gets information from different sensors—like the temperature sensor, airflow sensor, and crankshaft position sensor. In practice, this computer makes adjustments behind the scenes so that you can get better performance and fuel mileage.
If your ECU ever stops working, you must get a new one and program it. You can’t just get a new unit, plug it in, and expect it to work right out of the box. Therefore, get in touch with your local dealer to program the new ECU.
Notorious ECU Problems
The ECU pretty much controls your vehicle. So, if there’s something wrong with it, you can imagine all the problems you’ll run into. That said, here’s a list of some common symptoms:
Check Engine Light Comes On
We all panic when the check engine light comes on since it usually means trouble. And while it’s hard to tell why the engine light came on, it could be related to your ECU.
You see, the check engine light comes on when the vehicle’s computer picks up problems with any of the sensors. To rule this out, use your multimeter and test the ECU.
A failing ECU can produce a confusing range of problems. For example, if there’s something wrong with the computer, it can mess up the timing and fuel settings, which destroys your vehicle’s performance.
Car won’t Start
Generally speaking, if your vehicle won’t start, it means that there’s a problem with the battery. Perhaps, it does not have much time left. If that’s the case, you might be able to fix the problem by cleaning the terminals if they got corroded.
But if you’ve checked every possible scenario, you might have a problem with your ECU. If this unit is faulty, your vehicle will not start. The car might crank, but it won’t turn completely.
Your multimeter should read anywhere from 9 to 12 volts when testing the ECU. If you’re getting anything below that range, it means your ECU stopped working and must be replaced.
How to Test the ECU With a Multimeter
To test the ECU, we must test the continuity from the socket to the component. That said, here’s how to test car ECU with multimeter:
1. How to Test ECU Out of Car
Before removing the ECU from your vehicle, please take off the negative battery terminal. If you don’t disconnect the negative terminal, there’s a high chance you’ll fry the computer as soon as you pull it out.
Now locate the computer. Typically the computer is behind the glovebox. To pull it out, remove the screws holding the glove box, and it should come right off.
Now unplug all the electrical connections from the computer. Finally, remove the bolts holding the computer into the car.
2. Set up the Multimeter
After removing the ECU from the vehicle, set up your meter. To do this, insert the black lead into the “COM” side, then insert the remaining lead into the “VΩ” side. After that, set the multimeter to ohms.
Usually, this setting is represented by the Greek letter Omega. Turn the wheel to ohms, and you’re good to go.
3. Remove the Cover from the Socket
There’s a cover that protects the pins in the socket you removed from the ECU. That said, remove the cover from the socket. You should now have exposed the pins inside the socket.
4. Connect the Socket
Lastly, in how to test an ECU with a multimeter, grab the multimeter leads. Then insert them into the pins in your socket.
As you’re pressing them down, try to reach the back of the pin.
You should now get a stable reading on your multimeter. Anywhere from 0.67-0.70 is acceptable. For more information about this topic, watch this YouTube video:
How to Test ECM Input Sensors With a Multimeter
When testing your engine computer, it is crucial to diagnose the ECM input sensors. By testing the inputs, we will know if enough power is getting to the engine computer. So, here’s how to test ECU with multimeter:
1. Set up the Multimeter
First, take the black lead and put it where it says “COM,” then grab the other lead and put it in the “VΩ” jack. Next up, set the multimer to ohms.
2. Test Crankshaft Position Sensor
Hook up the leads to the sensor. Now grab a piece of metal and pass it through the sensor. The ohms on the screen should change, indicating that it’s registering the metal passing in front of it. In other words, the sensor is still in great shape.
3. Test Your Coolant Temperature Sensor
Attach the multimeter leads to the ends of the coolant temperature sensor. The meter should read about 2000 ohms. If you’re getting close to 2000 or higher, it means the sensor is still working.
4. Test Your Throttle Position Sensor
Connect your leads to the throttle position sensor. Rotate the throttle sensor, and the ohms on the multimeter should change smoothly. If you see a spike in one area, it means there’s something wrong with the sensor.
Frequently Asked Questions (FAQs)
Got any more questions about the ECU? Check this out:
How much is an ECU for a car?
- The average price for a new ECU ranges from $1,000 to $3,000. But you can also get a used ECU from a junkyard. If you’re working on an older vehicle, get one from one of those places, so long as it matches your exact original part number.
Can you drive with a faulty ECU?
- No, you cannot drive with a faulty ECU. You might be able to start up the engine. However, it might shut off as you’re going down the road. Therefore, get in touch with a certified professional to replace your ECU.
Can you test an ECU with a multimeter?
- Yes! You can use a multimeter to test an ECU and check for continuity. You can also use a scanner, attach it to your OBD port and see if you’re getting any codes from the computer.
What causes ECU to fail?
- Jump starting a vehicle is one of the most common ways to blow up the ECU.
The multimeter can be used for a lot of diagnosing on today’s machines. So, it is crucial to learn how to test ECU with multimeter.
You don’t need to spend thousands of dollars on professional equipment. Get a $20 multimeter, and you’ll be OK.
Also, don’t forget that you have to test the input sensors before assuming that the ECU is not working. If you’ve determined that the computer stopped working, change it as soon as possible to avoid further damage.