Here are the results of my efforts to solve the mystery of the red low level coolant light that never stops blinking. Some of you may be interested in trying to figure out how the electronics work. So far I have replaced everything. The light stoped blinking for several days after I installed a used temp gauge then started blinking constantly again. My next step will be to purchase a new gauge assembly from the dealer, but I really don't want to spend that amount of money and have the same problem occur again after several days. There are four components in the system. 1. (volt stab, part No. 171-919-803, around $10 from a VW dealer.) This is really a three prong 10v regulator which supplies a constant 10v to the temp gauge and the fuel gauge. One pin goes to 12v. One pin goes to ground, and the other pin supplies a regulated 10v. The tab also connects to ground and uses a large copper portion of the flexible wiring harness as a heat sink. 2. ( Cool low lvl wrng sw, part No. 251-919-372, around $20 from a VW dealer.) This isn't really a switch, but consists of two probes with about 1cm of exposed wire on the ends which extend into the water/antifreeze solution in the coolant expansion tank. A single wire connects one of the probes to pin S of the cool low lvl wrng contro unit (No. 2 below). The other probe is connected to ground 3. (Cool Low Lvl Wrng Cntro Unit, part No. 191-919-376A, around $30 from a VW deaer.) This is a plug in module mounted on the left side of the body beneath the dash. There are several other modules/relays attached at this same location. This one can be recognized by the markings on the bottom of the pins, G, 15, S, and 31. It also has two yellow/red wires attached to pin G. Pin 31 connects to ground. Pin 15 connects to +12v. Pin S goes to one probe of the cool low lvl wrng sw. Pin G connects to the negative terminal of the temp. gauge. (Note: There are other modules/relays mounted directly behind the fuses. These modules/relays are not the group of modules where the cool low lvl wrng cntro unit is located.) 4. (A gauge module consisting of temp. gauge, gas gauge, clock, part No. 251-919-511A, around $117 from the dealer. You can't buy just a temp gauge.) The temp gauge contains an integrated circuit consisting of one eight pin integrated circuit marked SEC 2741D0, two diodes, four resistors, one red LED, one 10mf capacitor. This circuit has three connections. One connection goes to the side of the temp gauge which is connected to the 10v voltage stab. One connection goes to the other side of the temp gauge which then connects to the cool temp sndng unit mounted on the engine. The third connection goes to a pin which connects to ground (the negative side of the 10v voltage stab. Anyway, that's what I have learned for what it's worth. I still have several questions. 1. What type of signal does the cool low lvl wrng cntrl unit output? 2. How does the circuit built into the temp guage work to detect the signal and cause the red diode to start blinking. 3. How does the circuit built into the temp guage test the diode upon turning on the ignition and then stop it from blinking. 4. A schematic diagram of the circuits. (not the wiring diagram from the Bentley) Hope I didn't take up too much space with this message. I'm looking forward to hearing from someone who can shed more light on this subject. |
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