Tech Tips From Transpo’s Rebuilder’s Forum Be on the lookout for this unit: a Nippondenso 102211-5380, 27060- 21040; as used on the 2000 Toyota Echo. It has a new terminal labeled “M” which is a feedback to the com- puter to control a coolant pre-heater. This terminal must have an output; measure with hertz scale or milli-volts. Motors and other devices utilizing coil windings or contacts generate volt- age spikes when disengaged or switched on and off. Voltage spikes generate when a magnetic field col- lapses. Uncontrolled voltage spikes in automotive electrical systems are of- ten detrimental to peripheral electronic components. Memory elements are particularly susceptible to transients. Transients may cause false data, strange vehicle behavior, or permanent damage to on-board micro-controller systems. Transients often exhibit high fre- quency characteristics. Modifying or changing conductor lead-length or lead position may alter the attenuation of a high-energy pulse, increasing the chance of stray RFI or EMI influence. Where voltage-drop diagnostics find the loose or poor connection, an os- cilloscope ‘with memory’ detects spikes and transients. One key component of a healthy vehicle electrical system is a fully charged, fully functional battery. A healthy battery effectively acts as a large capacitor, cushioning damaging transients. A sulfated battery no longer serves this purpose effectively. Ensure vehicle electronics are turned off when attaching or removing jumper cables or charger leads. Do not underestimate the neces- sity of proper grounding and tight, clean connections. When a high resistance connection forces voltage (with high current) to seek the next best path of least resistance, the end result can be serious. Protection is provided when OE manufacturers incorporate dedicated surge suppression devices. Some en- gineers take advantage of the alterna- tor bridge rectifier. Quality avalanche diodes respond quickly by clamping voltage spikes ahead of delicate mi- croprocessor circuitry. Where a stan- dard diode acts as an electrical check valve, an avalanche diode has the added feature ofa pressure relief valve; allowing voltage to reverse when it exceeds a specifically engineered threshold voltage. Your customer does not want to in- stall a rebuilt alternator that results in engine driveability or other micro-con- troller problems. Here’s a quick test for those of you whoare having difficulty diagnosing the polarity or type of field connection on generators. Using a good quality ohm- meter, disconnect all wires from the generator. Measure the ohms from “F” to case. Then measure the ohms from “F” to “A” or armature (ARM) termi- nal. If the lowest reading obtained is “F” to “A” then the generator is an A circuit. If the lowest reading is “F” to case then the generator is a B circuit. If there is little difference in the readings then you may have to pre- vent the brush from contacting the ar- mature. Place a piece of thick paper between the brush and armature and take a second set of readings. If you still get low readings then you have a field shorted to the case. Reprinted with permission from Transpo Rebuilder’s Forum. APRIL, 2001 Page 1 of 1