Why Resistance Checks Don’t Always Work

Written by Chris Adams, Diagnostician

I think I can safely say that we have all been here before: “I ohm-checked the entire circuit and it checks OK.” This article started as a problem found on a particular vehicle, and then it morphed into an article on - in my opinion - a better, faster, more efficient way of checking electrical circuits on a vehicle. In this example I want to show how amperage-based testing on a live circuit can save you time and headaches versus traditional resistance testing on a dormant circuit.

AX4N (4F50N) Harsh 1-2 Shift

Written by Jody Carnahan

I received a call from one of our wholesale customers which is a shop that does general repair and transmission work on occasion. He called looking for help on a 2004 Ford Freestar that he could not get to leave his shop. In fact, the vehicle has been to several other shops in the past. He advised me that the transmission had been worked on recently by another shop and that it was now back in his shop. I asked him what the previous failure was and he indicated that it was a problem with a 2^nd gear slip. They had removed the transmission and found the intermediate clutch piston bonded seal was damaged and that was all that was done to repair the unit. Now that they have it all back together, the trans bangs hard on the 1-2 shift. It was not setting any codes and from what the shop could tell everything with the vehicle and load sensors were working properly. I decided to take on this challenge and advised him to drop the vehicle off at our shop.