Tech tips From a battery drain to the fuel pump blues YUKON EXHIBITS MYSTERY Y BATTERY DRAIN A customer rolled in (or should I say was towed in) with a 2002 GMCC Yukon, complaining of a constant battery drain. The engine won’t start in the morning, she charges the battery, starts and runs it, but after parking it for a few hours, the battery’s dead again. To make a long story short, the charging system was working fne, but there was a parasitic draw somewhere. We traced the problem to a he autofaulty blower motor processor for the matic temperature control system, which was causing the blower motor to run continuously, even with the key off. The faults were traced to the automatic climate control processor (actually a resistor) and the blower motor. As it turns out, the processor was fried, so we initially assumed that replacing it would do the trick. However, during investigation, we noticed that the blower motor was bad, which in turn seems to have taken out the processor. The processor was obtained for $280 (which seems way too much for this little guy). After replacing the blower motor and processor (easy access), the repair was complete.
HONDA CHARGING Even though Honda has used the Electronic Load Detection (ELD) System since 1988 on the Civic and 1990 on the Accord, there is still a lot of confusion on how this system operates and controls the charging system. The ELD system inputs the electrical load to the engine control module (ECM), and then the ECM controls the output of the alternator under various electrical loads, and is capable of shutting the alternator off completely under very low or no load
situations. When the vehicle is frst started, the alternator may not begin charging for up to three minutes. Before performing any tests on the charging system, be sure to put an electrical load on the vehicle’s electrical system by turning on the headlights or turning on the blower motor or rear defogger. The ELD unit, located in the underhood fuse box, must sense current fow through the fuse box so it can correctly indicate the electrical load on the vehicle to the engine control module (ECM). The ELD unit has three wires leading to it, a 12-volt power supply wire, a ground wire and a signal wire. On the signal wire the ECM will send a reference voltage of approximately 4.5 to 5 volts to the ELD unit. The ELD will pull this reference voltage towards ground depending upon the amount of load on the electrical system. With no or little current fow through the ELD, the ECM will see approximately 3.5 volts on the signal wire. At this time, the ECM can ground the control wire at the alternator and the voltage regulator will turn off the alternator without illuminating the charge light. If the current fow is high, the voltage on the signal wire will be close to one volt.
66 | January/February 2014
