Engine Controls - Never Use a Test Light To Check an ECM

NO.
TSB-92-00-003

DATE
August, 1992

MODEL
All Models, All Years


SUBJECT:
ECU CIRCUIT TESTING PRECAUTIONS



PURPOSE





This bulletin is issued to remind technicians NOT to use a test light when checking computer controlled circuits. A Digital Volt-Ohm Meter (DVOM) should be used whenever checking the voltage in any computer circuit. NEVER USE A TEST LIGHT TO CHECK ANY COMPUTER CIRCUIT.

DETAILS

Electronic Control Units (ECU) returned for failure analysis contain burnt transistors. This type of transistor damage is typically caused by excessive current demands. Research has proven that ECU damage can and will occur during diagnosis by using a test light to check for voltage in computer circuits. A test light bulb, in order to light, will draw a considerable amount of current from the circuit being tested. In some cases, high current flow overloads solid state components causing damage.

A Digital Volt-Ohm Meter is the preferred measurement device for checking computer system voltages. Of limited alternate use, an Light Emitting Diode (L.E.D.) tester (logic probe), or lab-type oscilloscope can be used during some tests. These devices draw only a very small amount of current from the tested circuit.

NEVER USE A TEST LIGHT TO CHECK COMPUTER CIRCUITS.