Vehicle information
A 2008 Volkswagen Passat Pilot 1.8T sedan with a mileage of about 176,000km. The car sometimes has difficulty starting. Let’s take a look at what causes it, shall we?
Diagnostic analysis
Repair personnel test drive, the fault can not be reproduced for a while. Detect the engine control unit, there is no fault code. Test other control units, instrumentation control unit fault code “01314 an engine control unit does not communicate” exists.
The fault codes recorded in the instrument control unit were analyzed to indicate that the engine control unit was not working at times and that the difficulty in starting should be related to this problem. First check the power wiring to the engine control unit, which includes fuse SC17, and relay J271 (648), no problems were found. Measure the oil pressure, it is 350 kPa and shows normal.
Next, all the hitch points were removed to clean and tighten them. Strangely enough, the engine failed to start at all after these treatments, which means that the occasional fault has finally become a current fault. The test engine control unit found that there are two fault codes: P1531 – intake camshaft control circuit disconnection; and P1545 – throttle control system failure.
Viewing the data stream shows throttle matching error #1. In repeated tests, the throttle could not be matched and always showed the fault. 62 sets of data for zones 3 and 4 changed with the accelerator pedal, but there was no response to the throttle opening shown in zones 1 and 2. Replace the throttle and the fault remains.
A look at the wiring diagram reveals that the main relay is directly supplying power to the camshaft phasing control solenoid N205. The fault code suggests that this solenoid is disconnected, does this mean that it is not getting power? If so, the injectors, ignition coils, and throttle naturally don’t get power either, so the engine won’t start. Also, when the starter is running, the supply voltage is pulled down and the problem is exacerbated.
Troubleshooting
Replace the main relay and test drive, the vehicle can start normally.
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