u I have a few comments regarding your
Electronic Diagnostics feature about the VW Golf 1.6 FSI (CM, August 2017). I was confused by your saying the car was fitted with a BLP engine. With the Golf MKV, the BLP engine was only fitted for the 2005 model year, specifically from May 2004 to July 2005. As the subject car was a 2008 model, it could not have a BLP engine. I suspect it was probably a BLF engine. Although the two are closely related, there are a number of important differences, such as the BLP having the very failure-prone and extremely expensive combination NTK brand NOX sensor. Also, the BLP engine uses 98RON fuel as a minimum, whereas the BLF can use 95RON.
This generation of Golf ECU uses the Bosch Motronic MED 9.5.10 management system. The designation 03C 906 056 EM quoted in the article is the VAG part number.
The brake pedal operated switch is a dual pole unit which sends two separate signals, one to the ECU and the other to the brake light input of the onboard supply control unit and the ABS pump ECU. These two signals must be detected together or the ECU drops into safety mode. If the ECU input fails, the brake lights will still work.
You say that if the bonnet switch fails in the open position it will stop the wipers from operating (they do work after around 20mph, though), but the switch is also linked to the instruments, not just for an open warning but also because it works with the oil level detection system to indicate if the bonnet has been opened after a low-level warning.
The in-tank lift pump gets a mention, but not the problematic high-pressure pump mounted on the cam cover.
A fast way to tell if a misfire is due to a burned exhaust valve is to clear the codes with the engine running. If the misfire clears for a while, this shows that it is the ECU shutting down the injector on a cylinder that it has detected as producing excessive emissions. This is a useful quick test if buying a vehicle with a problem should a compression check not be practical.
The pre-cat Bosch LSU-4.9 wideband sensor and the post-cat Bosch LSF-4.2 narrowband sensor on the BLF engine can be tested using a diagnostic system that is capable of accessing the Basic Settings function of the ECU in data groups 028 and 030 upwards. This is a very effective way of checking your work – it is known as ‘setting the Readiness Code’.
The Golf MKV has a unique and overly complex door design where accessing the internals means the skin must be removed. To do this, the door has to be open. In the event of the door lock unit not operating, taking off the interior door panel with the door closed is almost impossible without damaging the doorcard’s forward mounts and you will be sorely disappointed to be confronted by a sheet of metal! Opening one of these doors when jammed is one of the biggest problems I have ever encountered in 33 years of working on VWS. Thank goodness they changed back to a conventional design on the Golf MKVI! Steve C
Martyn Knowles responds: Thanks for the additional info, Steve. We did get the engine code wrong on this occasion. The 2008 car we diagnosed does have the BLF reference. Also, only half of the circuit diagram for the Motronic MED management system was printed. We’ve reproduced the diagram in full on page 80.