Tap Test GM Tap Test General Motors bulletin # T-92-7 General Motors advised in their bulletin # T-92-7 that the testing of a ECM should be done with the fingertips of one hand, against the top of the ECM case. If you tap the bottom of the ECM case, you chance causing enough deflection of the case bringing it into contact with the electrical leads on the bottom of the circuit board. Use your palm, fist, or any other tool(s) may subject the case and circuit board of the ECM to stress beyond its' design limits. If the case begins to flex, the internal circuit board will flex. This can cause the Integrated Circuit chips (IS) to break away from the circuit board creating a possible ECM failure or intermittent drivability problems. Visit our Resource Library for available downloads