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Dear all,
I have a problem engine light on and glowplug blinking.
According to my Mechanic, this will cause engine to start only. But since my country is hot weather whole year (Malaysia), my mechanic said it is ok with one glowplug failed without need to change.
Is it ok, to keep run with One falied Glowplug? Reason why I not changing is, according to Mechanic Glowplug is for starting cold weather (which is not my country). Is it true, I can just ignore the glowplug error?
Having a non-functional glow plug puts your system out of balance when cold starting the engine. Seriously, unless it's like ambient temp is never below 90 degrees F outside or where the car is parked, then you are creating a problem by not replacing the busted glow plug. The glow plugs function based on the temperature sensors on the car...primarily the coolant temp sensors. It doesn't need to be cold outdoors for the glow plugs to be active; their purpose is to work as one unit to preheat the air inside each cylinder in order to support 'spontaneous combustion' since this is a compression-based engine. Glow plugs not only work during the 'preheat' stage, but also continue to heat the cylinders during their 'afterglow' phase, which can last for several minutes until the car's internal temp sensors tell them to turn off, etc.
Here's a pretty good reference/overview of the glow plugs system and how it operates. Hopefully this provides necessary perspective. You can always look up the exact data on how/when the glow plugs are functional. What follows herein I copied over from an archival thread on this same topic:
So much (mis) information here, some good some bad.
First, the TDI's glow system operates at every start from ambient temps on any day of the year in any state or province in North America. Yes, you read that correctly. Your car sat overnight in August in Florida, guess what? When you start your car up, the plugs get powered up.
Now, for how long (both for the pre-glow and post-glow) depends on coolant temp and RPM.
The indicator in the cluster is NOT an indicator of whether or not the plugs are powered up, but an indicator of when the system says you can start the engine. The plugs may remain powered up, under 2500 RPM, for several minutes... longer periods in the cold. This is normal. This is called afterglow, post glow, or whatever, and is intended mainly for smooth running and lower emissions during warm up. Older (pre-TDI) VAG diesels did not do this. Their post glow was about 3 seconds, and once the relay clicked off, it stayed off.
Pre-2002 TDIs have their glow plug relay in the inside of the car, in the relay box, and it is normal to hear it clicking on and off as the car warms up. Every time you sweep over 2500 RPMs, it clicks off. Then back on again when it sweeps below 2500 RPMs. It will do this until the coolant is up to a temp predetermined by the ECU's programming that says "OK, the engine is warm enough, we can keep the plugs off". 2002+ cars placed the relay outside the car, near the ECU (on Golf/Jetta/NB) and under the coolant bottle (on Passats) and they are actually a slightly different functioning relay (duty cycled) but that is not important right now.
If you feel your preglow period is somewhat short, meaning the time the light stays lit, you *may* have a faulty coolant temp sensor that is not giving the correct value to the ECU. So, if it is 25 F out, and your ECU is getting a signal that it is 75 F, the preglow will be shorter than ideal. But since 70 F is within the normal range of the CTS, the ECU will not flag this as a fault.
While you can electronically lengthen the preglow period with VCDS or similar on many cars, keep in mind these items:
1: some light smoke on a cold start and during warm up is normal It is even stated in the owner's manual.
2: improper timing of the pump, a worn pump, poor injector spray pattern, poor fuel, weak compression, etc. can also cause some excessive whitish smoke after a cold start.
3: a weak battery can also cause excessive smoking, as not only will the engine not crank as fast as it should, the glow system will be placing a massive drain on it both before and after the starter has done its job, further increasing smoke as the electricity to the plugs is reduced and they won't get as hot as quickly.
I have started countless TDIs up cold, have owned them from new all the way to nearly 400k miles, VEs and PDs, and they should all start right up down to single digit (F) temps without too much drama. However, they are all going to put some puff of something out the tailpipe. It may not be enough to see every time, but standing behind the car you'll see something and again, this is normal.
Last edited by '10Q7TDI_Prestige'; Feb 1, 2025 at 03:04 PM.
Just glancing at that actual fault code shown on the picture, and thinking about the other fault codes indicated on scan tool that you aren't showing us, which could be relevant, but perhaps not:
An open circuit fault could mean the glow plug is now internally faulty, but could also indicate that there's a break in the wiring or the actual connector that connects to the glow plug has come off, etc., or even from rodent chewing on wires type damage, etc.
Here's a reference as to how to interpret this fault code (05663):
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