Jordan Hill is an ASE Master Certified Technician with over 24 years of experience diagnosing and repairing all makes and models, from domestic light trucks to high-performance imports. Known for his expertise in advanced diagnostics, electrical troubleshooting, ADAS calibration, and hybrid/electric vehicle systems, Jordan has managed shops, led teams, and mentored the next generation of technicians. His work blends hands-on mechanical skill with cutting-edge technology, including factory scan tools, lab scopes, and remote diagnostic platforms.... Read more
Rushit Hila is the founder of YOUCANIC and a passionate advocate for empowering car owners through knowledge. With a background in automotive diagnostics and years of hands-on repair experience, Rushit leads the YOUCANIC team in creating practical, easy-to-follow guides and tools that help drivers fix their own vehicles. His mission is simple: make car repair less intimidating and more accessible for everyone.
A diagnosis can take many twists and turns before one finally lands on the right solution. One such example of staying the course during troubleshooting came with the subject of this fix, a 2012 Volkswagen (VW) Jetta. This car, equipped with a 2.0L CJAA TDI engine, was referred to us from another shop. It was suffering from an intermittent flashing glow plug light, check engine light, and reduced power mode.
The turbocharger assembly had already been replaced, but the symptoms persisted. (I must admit that selfishly, I enjoy these kinds of repairs, as they often have interesting results, and this Jetta did not disappoint.) For those who don’t know, Volkswagen uses the glow plug light as a general failure warning; it does not specifically mean there is a problem with the glow plug system.
Glow plugs are the sparkplugs of diesel engines. They are heating devices found in diesel engines to help the car start. There may be a glow plug fault, but the warning light could also point to a number of other issues with the engine management, turbocharger, or even a faulty brake light bulb. Eventually, if the vehicle continues to be driven, the engine may enter reduced power mode to limit throttle response and engine RPMs.
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A road test, fault scan, and basic under-hood checks of fluid levels and battery condition were carried out. While the flashing glow plug light was not present on the test drive, we made a noteworthy discovery. The brake pedal felt hard at times, like the power booster was weak. I made a note of the issue for future reference.
The fault scan also did not disappoint. I found the code P2563 during the initial scan for the Turbocharger Boost Control Position Sensor Circuit Range/Performance. The Turbo Boost Position Sensor is mounted to the turbo assembly and is used to monitor the position of the variable turbo vanes. This sensor is part of the turbo assembly, which is the main reason the original shop replaced the turbocharger. Now it was time to try and verify the symptoms of this Jetta.
After recording the data from our initial scan, the code was cleared, and a second road test was conducted to try and duplicate the intermittently flashing warning light. The term ‘intermittent’ is really a misnomer; even the most random of problems have specific conditions under which they occur. The key is figuring out what conditions cause the problem to act up. When the conditions are determined, then the intermittent condition loses its power of randomness.
In this case, it took some trial and error, but I was able to replicate the fault conditions. By sitting at idle with the manual transmission in gear and pumping the brake pedal several times in succession, the glow plug light would start flashing, and the P2563 fault would be stored in the ECM. This was consistent and repeatable, and the jumping-off point for solving the Jetta.
This new clue turned my attention away from the turbocharger and towards the brake booster, or more precisely, towards the vacuum source for the brake booster. Since this was a diesel engine, a small vacuum was produced by the engine itself, unlike a gasoline engine, where a vacuum is created from the downward motion of the pistons pulling against the closed throttle blade.
This TDI (Turbocharged Direct Injection) engine used a mechanical vacuum pump driven off the back of the intake camshaft. The vacuum pump directly feeds the power brake booster and has a…
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