Today's cars are overloaded with electronics and the Onboard diagnostic systems are starting to have issues. Not long ago the glow plugs were controlled through a simple relay that didn't cost much. Today the plugs are controlled by expensive "Intelligent Control Units".
"If they are intelligent" we would expect that they can detect that the glow plugs are not working. Unfortunately, they don't have this ability! The Onboard diagnostics system doesn't detect that not a single glow plug is working. It looks like the VW programmer was working on the software on a Friday afternoon or he simply didn't know what he was doing.
Even when the engine is cranked for minutes without the engine starting, not a single Fault Code is stored in memory indicating a problem with the preheating system. To make this even more frustrating the engine MIL light turns On and a DTC "Fuel Pressure Too Low" is set.
Nine out of ten mechanics will start looking for a low fuel pressure issue. We should stress at the beginning that these attempts lead to nowhere. The fuel pressure was low due to a weak battery that was tired from the unsuccessful attempts to start the engine in cold weather (information is available in Freeze Frame).
The mechanic will usually respond by saying "I am going to look at the engine Preheating system" as a quick response to the owner's statement that the engine doesn't want to start if the car is not used for a few days and when the ambient temperatures are low. The owner's face will look satisfied thinking "finally a mechanic who seems to know what he is doing". (Note: No, this mechanic doesn't know what he is doing. To be more specific he is just applying his usual and incorrect procedure.)
The mechanic tests the individual glow plugs directly and finds one glow plug with lower performance. He tells the owner that he will replace all the glow plugs because if one is having problems the remaining will probably have problems in a short time anyway. The owner agrees and the mechanic installs new brand-name glow plugs.
The owner pays for 4 new glow plugs and collects the car from the workshop. The following morning the car cannot be started. The only trouble code is again pointing to "Low fuel pressure in the rail". Once again there is an issue with a weak battery that has reduced power from the fifteen ten-second-long cranking attempts.
The owner discovers FCD and arranges to have the car diagnosed. This was in a situation where the owner didn't know what to do and where to go anymore. The car symptoms were difficult starting during the whole winter and including situations where the car wouldn't start and the owner couldn't drive the car at all.
The car has no problem starting in a warm workshop. We connected everything that can be connected. We are monitoring the values of both fuel pressures (high & low delivery), the compression, the engine cranking speed, the injected cranking fuel quantity and finally, also the preheating system is tested. From the recordings, we can see that everything is working as it should during cold-weather starting. The only system that has an issue is the engine preheating system which is not working at all.
The module costs over 100 Eur and is less intelligent than the old original preheating relay. When the module fails the car owner doesn't know and workshops working in 80% cases only with trouble codes don't know either that the module is not working. After 2 minutes of attempting without success to start the engine, there is no feedback that the "preheating system" is not working! What is even more worrying is that after longer cranking periods a Fault Code "Rail fuel pressure too low" is set. The car has no issue with fuel pressure and the Fault Code is triggered by the tired battery.
The engine is cold enough and one attempt with a Log recording reveals where the problem is. The preheating system is not working at all. After 6 long cranking attempts, there is no fault code set indicating that the preheating system is completely non-functional! All the new glow plugs (replaced in the previous workshop) are not working at all. The FCD website explains how to test the preheating system correctly and effectively.
On cars with DPF filters, the preheating system is active even during summer and after every cold start. This reduces the generation of soot that is always the highest after every cold engine start. The soot generated by a defective preheating system then damages the engine due to frequent regenerations.
The module costs over 100 Eur and is less intelligent than the old original preheating relay. When the module fails the car owner doesn't know and workshops working in 80% cases only with trouble codes don't know either that the module is not working. After 2 minutes of attempting without success to start the engine, there is no feedback that the "preheating system" is not working! What is even more worrying is that after longer cranking periods a Fault Code "Rail fuel pressure too low" is set. The car has no issue with fuel pressure and the Fault Code is triggered by the tired battery.
The engine is cold enough and one attempt with a Log recording reveals where the problem is. The preheating system is not working at all. After 6 long cranking attempts, there is no fault code set indicating that the preheating system is completely non-functional! All the new glow plugs (replaced in the previous workshop) are not working at all. The FCD website explains how to test the preheating system correctly and effectively.
On cars with DPF filters, the preheating system is active even during summer and after every cold start. This reduces the generation of soot that is always the highest after every cold engine start. The soot generated by a defective preheating system then damages the engine due to frequent regenerations.
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