A Honda Accord came into the shop with only a few thousand miles on it and a check engine light. It had a code for no signal from the radiator coolant temperature sensor, so I got started on electrical diagnostics.
Following the Honda diagnostic tree, I checked to see whether the sensor was getting a signal and had a good ground, and after a little while determined that one of the wires must be broken. Trying to find a broken wire in the mass of wiring harnesses in modern cars sounds like a nightmare, but I got very lucky and found it quickly.
I found that the owner had hit something in the road with the front of the car, and besides damaging the bumper and undershields just a little bit, it actually damaged the front wiring harness as well, breaking the wire for the radiator coolant temperature sensor. On a nearly-new car, I wouldn’t want to try to repair a broken sensor wire like this unless I absolutely had to, so a new harness was the repair needed. Fortunately for the customer, this didn’t need the entire engine bay harness, just a small front end harness that wasn’t too expensive. All I needed to do was remove the front bumper to replace it.
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