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Thermal Imaging and Parasitic Draw, by Scott Shotton

I recently purchased a thermal imaging camera, the Autel MaxiIRT IR100, and was excited to see how well the tool functioned and how well the diagnostic techniques I have been hearing about work. As a result, this article will serve both of those purposes.

MaxiIRT IR100 Thermal Imaging Camera


Conveniently, a few days after I received the IR100, I got a call from a shop that had a 2007 Honda Odyssey with a battery that would go dead if the vehicle sat for a day or two.

Upon arrival at the shop I was informed that there was approximately an 800 mA draw which I confirmed with a Fluke ammeter. Before digging too far, a quick visual inspection revealed some aftermarket wiring and “boxes” under the dash. Before going any further a thermal image of these components was taken. The Autel IR100 allows the option to see 3 views:
- 100% thermal signature
- 100% unfiltered image (no thermal signature)
- 50%/50%combinations of both.

In figure 1, the left side of the image is completely thermal while the right side of the image is a mix. Figure 2 is an image of the installed aftermarket components with no thermal signature and the components after being removed from the vehicle.

Autel MaxiIRT IR100 image of component with current flowing, by Scott Shotton
Fig. 1: Thermal imaging of a component that has current flowing.

Autel MaxiIRT IR100 image of component with current flowing, by Scott Shotton
Fig. 2: Normal images of the same aftermarket components shown in figure 1.


After disconnecting the aftermarket "boxes" the next step was to confirm the draw was gone. Figure 3 (below) shows the draw only dropped to 430 mA so more testing will be required. A note about the IR100 image: the quality of the non-thermal image is not too great. To me this is no big deal because I am not using the tool to gather high quality images. If I wanted a higher quality image, I would simply use another camera or my cell phone. Diagnostically the tool is serving its purpose to this point.
Autel MaxiIRT IR100 image of 430 mA draw, by Scott ShottonFig. 3: A 430 mA draw still exists after removal of the aftermarket components.


The next step was to look elsewhere for the remainder of the parasitic draw. The thermal camera was pointed at the under-hood fuse box and image 4 (below) was taken. Near the top-center of the image, the glowing yellow rectangle just so happens to be fuse #15. This shows that it only takes a small amount of current to generate heat. Testing in this manner allows the technician to narrow down suspect circuits without disconnecting anything. To me, this is valuable. I do not like to remove fuses unless I have to because I do not want to accidentally wake up a module, or component, extending my diagnostic time while I wait for things to go back to sleep.

Autel MaxiIRT IR100 image of fuse generating heat, by Scott Shotton
Fig. 4: Fuse #15 in the under-hood fuse box generating heat due to current flow.


Consulting a power distribution wiring diagram revealed that fuse #15 feeds power to multiple fuses in the driver’s side under-dash fuse box. The IR100 was used here as well and fuse #7 was generating heat (Sorry, I forgot to save the image of fuse #7). Further analysis of wiring diagrams showed that this fuse fed power to multiple modules: the immobilizer module, turn signal switch, gage control module, rear MICU and both power sliding door modules. The camera was used to observe all of these modules until a heat signature was found. In this case, the right power sliding door module (Fig. 5 below) was glowing brightly. 

Autel MaxiIRT power sliding door with current flowing, by Scott Shotton
Fig. 5: The right power sliding door module has current flowing when it should not be.


When the door module was disconnected the parasitic draw went down to an acceptable 20 mA. Being a beater work van, the customer opted to leave the module disconnected and operate the right-side slider manually.

I believe that my experimenting with this tool and the techniques confirmed that the IR100 functions very well and the procedures outlined above most likely saved valuable diagnostic time. However, I did find a caution. I was curious how sensitive the tool really is so I experimented again. In figure 6 (below), you can see the left of the image is the plastic trim panel under the hood. I wanted to see how long heat would remain. So I placed my hand on the panel for 15 seconds to allow my body heat to transfer to the plastic. I did this at about 11:23. Then I monitored the temperature periodically for the next few minutes. The right side of the image is from 3 minutes later and heat is still visible.

Fig. 6: Measuring heat transfer and how long it takes to dissipate. Thermal image shows heat signature 3 minutes after 15 seconds of hand contact on the plastic housing.

The IR100 is extremely sensitive, which is good, but caution needs to be used when observing warm components. For example, if a fuse was hot 1 minute ago it might still have a heat signature now. When using thermal imaging, make sure you wait a sufficient amount of time to get an accurate reading.

So far, my only complaint with the IR100, and it is a minimal one, is the image save function. Each time you pull the trigger to capture the current screen image you are prompted with: save image yes/no. The only reason I did not like this prompt is when crawling under a dashboard and snapping pictures it is inconvenient to perform the extra button presses required to save the image. An auto-save function with each trigger pull would be nice. I should read the manual a little more closely and see if this is an option. If that is my only issue I will continue to use the Autel MaxiIRT IR100.

Update: I discovered there is a short-cut to saving the captured image. Initially the image is obtained by pulling the trigger. When the save "yes/no" menu is displayed, simply pull the trigger a second time and it defaults to "yes." Live and learn!

Autel MaxiIRT IR100 Thermal Camera details