Wednesday, October 20, 2021

Diagnosing a Bad Diagnostic Tool

Yesterday I woke up early and drove the 15 miles to Alta ski area so I could do some early season skiing. We received about 25-inches of snow last week and then another foot or so on Monday evening. No the lifts are not yet running and so skiing requires hiking up the mountain. When you have the right equipment, it is a great form of exercise and fun. If you don't have the right equipment it is still a great form of exercise but not nearly as fun.

Last night I took a look at the statistics from my Suunto smartwatch and realized that it must have missed a few of my heartbeats during my hike up the mountain. The watch is generally very accurate but the readings I got yesterday are definitely low. When I go running up a hill with skis on, my average heart rate is around 120-130 beats per minute. The reading I got yesterday was a lowly 65. I know that is not right as there is always an informal competition with anyone else climbing the hill. You want to pass other people and never get passed. That means I could feel my heart beating quite noticeably by the time I got to the top of the hill. It was well past the 65 beats per minute.

On Monday I had a different experience but one that sort of relates. Follow me for a moment and you'll see what I mean. My wife's Jeep's check-engine light came on. I pulled out my trusty OBD-II computer and connected it to the car using the port under the steering wheel. I waited for the error code but only got an error reading the Jeep's computer. I tried several more times making sure to re-seat the connecting cable with the same results. Our son came over with his OBD-II reader but it also failed to read the error code from the car. Now what do I do?

Fortunately Jeep Wranglers have a way to read the diagnostic codes without having to use an OBD-II reader. You just need to turn the car on and off 3 times without starting the vehicle. Then the code appears in the odometer. It took me a few times as you have to go quickly and I was going too slow. The car spit out the code and it told me where to start looking for the problem. Basically the thermostat was bad. I had to do more to make sure that was the problem but then I replaced the thermostat for $25 and about an hour of my time. That $25 included the new thermostat and a gallon of engine coolant.

So what do these two stories have in common? Sometimes your diagnostic tool will give you erroneous information. If I had been relying on my smartwatch to give me my heart rate, I would be mistaken. Fortunately there is an easy check you can do yourself to get your real heart rate: look at your watch for 15 seconds, count heart beats, and multiply the result by 4. With the OBD-II computers, I got worried that the car had another fault with the connection. When 1 reader doesn't work, you can guess the reader is bad. When 2 don't, you start to get really worried. Fortunately I ordered a new OBD-II reader as my old one is over a decade old and needed to be replaced anyways. The new reader arrived yesterday afternoon and I was able to access the code and reset the Jeep's computer.

Diagnostic tools generally work fairly well. You just can't trust them blindly as you may be tracking down the wrong problem. Verify the results through other means if possible. Once I had a starting point on my wife's car, I could put my hand on the coolant hoses and verify that the thermostat was stuck in the open position before starting any work on the car.

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