![]() After study of the datasheets the input signal from the ECM will be used as a clock for the Data Out line and the input signal pulse should be the inverse of what you want on the glowplugs. These are obsolete parts but you can still find the datasheets online. Inside the GCM there’s one main IC, an ST Microsystems L9524 glowplug controller and four ST P85NF55L MOSFETs that do the actual pulsing of the glowplug voltage. And you can imagine what fun it is to troubleshoot this at very cold temperatures. If I connected the glowplugs to the battery through some resistance wire to drop the voltage to 7V, the Jeep started without difficulty. That is, the glowplugs should be on 62% of the time, not the 38% I was seeing. 7 volts is about 62% of a 12V battery, so you should see a pulse duty cycle of about 62%. Far too little, you barely see it glow at all at the end of a few 14 second cycles with your hands cupped around it. The glowplugs show a 11.5Vp-p pulse at 31hz with a 38.6% duty cycle. And they should glow red brightly when you bench test them, something I didn’t know, though it seems obvious now. They’re either good or they’re not, like an incandescent light bulb. BTW, I must state that glowplugs or any heating element like them, say in a stove or hot water tank, do not get weak. With a Fluke DMM, the Passat glowplug voltage would be about 4.1Vdc, 5.7A for about a 13 second cycle after you turn the key. I’m a retired electronics technician, so I’ll list the info I have. I went through quite a lot of trouble to find this, but both vehicles use Bosch glowplug control modules (GCM) and while they weren’t the problem, the pulse-width modulated (PWM) signal from the engine control module was. They both developed difficulty in starting in cold weather, noticeable below 0 celsius, and progressively harder as it gets colder. ![]() Two completely different vehicles, with the same symptoms and the same root cause. We have both a 2005 Passat 2.0L TDI and a 2006 Jeep Liberty 2.8L CRD. I rarely post to forums, but this is such an unexpected problem I feel I should share. 2006 Liberty CRD and 2005 Passat - ECM Glowplug Control Signal Issue, Arduino Solution
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |