A 2006 Volkswagen Passat Pilot 1.8T sedan with a mileage of about 87,000km. Users reflect The car driving engine EPC light alarm, asked to come to the factory to check, let us see how to solve this.
Fault diagnosis
The first routine inspection, with diagnostic instrument VAS6150B, reads the system data, the presence of 17072 power main relay disconnection / short circuit fault code.
Check the relevant circuit diagrams, that J271 is the power supply main relay, on the relay J271 also control the engine 4 cylinders independent ignition coil power and camshaft timing adjustment valve power, then, J271 itself will affect the engine’s fault; in addition, J220 engine control unit also need to be judged.
Replacement of the main relay
It was more convenient to try replacing one of the main relays first, but the result was still not troubleshooting. As the engine control unit failure probability is small and has been the history of the previous replacement of the main relay J271, the next focus is to check the wiring between the main relay and the engine control unit, as well as the J271 power supply components of the wiring is good.
Turn off the power, remove the J220, measured V J271 main relay 1/86a pin voltage of 12.31V; 4/85 pin to T121/21 pin line resistance of 0.472; to ground to positive infinity; 2/30, 1/86a pin, T121/62 pin resistance between the two are 0.42, normal.
Since the main relay end checks out fine, focus on the wiring downstream of the J271 main relay control. Downstream of this were the camshaft adjustment valve controlled by fuse S331 and the ignition coil and J220 power supply controlled by fuse S229. When measuring pin T10e/1 to pin T121/121, the resistance value was normal at first, but when the wires were shaken to test the positive value was found to swing at 1.37k only. It seems that the problem is in the line. According to the circuit diagram, dismantling the section of the line in the D3 connection point, found the parallel line at the de-soldering phenomenon.
Troubleshooting
The fault occurs in the vehicle bumps after the EPC alarm, and the final point of failure is due to the connection point desoldering caused by intermittent failure. Therefore, in future maintenance, first of all, need to ask the user in detail, because only the user is most clear about the fault that occurred when the vehicle is driving status, which is conducive to narrowing the scope of the technician to determine the fault. For this kind of electrical failure repair, more should be carefully checked according to the circuit diagram of each component line connection line focusing on measurement data.
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