Causes of a flashing glow plug light

Because this is a frequently asked question, I went digging through info for '01 ALH and made the following list of known reasons for the glow plug light to flash. They are listed with the VW code and generic reader P code.

00741 Brake pedal monitoring - implausible signal
01044 Control unit incorrectly coded
16705/P0321 Engine speed sensor - implausible signal
16706/P0322 Engine speed sensor - no signal
16955/P0571 Brake light switch (F) - implausible signal
17653/P1245 Needle lift sender (G80) - short to earth
17654/P1246 Needle lift sender (G80) - Implausible signal
17655/P1247 Needle lift sender (G80) - Open circuit/short to positive
17762/P1354 Modulating piston movement sender (G149) - electrical fault in current circuit
17969/P1561 Metering adjuster (N146) - control difference
17978/P1570 Engine control unit blocked
18020/P1612 Control unit incorrectly coded
18026/P1618 Glow plug relay (J52) - short to positive
18027/P1619 Glow plug relay (J52) - open circuit/short to earth
18040/P1632 Accelerator position sender - voltage supply

It also flashes when an interface tool has put the ECM in 'basic settings' mode.

There may be more; these are the ones I found documented.

The brake light monitoring includes the clutch switch (manual transmission cars). It also includes a possibility of blown brake light bulbs.

This is great information. Now I know why you get a flashing glow plug light when trying to run European Rocketchip programs on non converted ALH ECU's. It could be any of theses:

01044 Control unit incorrectly coded
16705/P0321 Engine speed sensor - implausible signal
16706/P0322 Engine speed sensor - no signal
17653/P1245 Needle lift sender (G80) - short to earth
17654/P1246 Needle lift sender (G80) - Implausible signal
17655/P1247 Needle lift sender (G80) - Open circuit/short to positive
17762/P1354 Modulating piston movement sender (G149) - electrical fault in current circuit
17969/P1561 Metering adjuster (N146) - control difference
17978/P1570 Engine control unit blocked
18020/P1612 Control unit incorrectly coded

L

Way to go MO, aka good work...

MOGolf said:

It also flashes when an interface tool has put the ECM in 'basic settings' mode.

Click to expand...

Thanks

Sounds like that should be a sticky in TDI 101's How To thread.

Would any of those codes render the car dangerous to drive? Would it damage the engine?

That glow plug light just started to blink....

Thanks,

Flashing Glow Plug Light - No Code

I have a flashing glow plug light and my SGII is not picking up any codes. What could be the problem?

mine's been flashing for months. Implausible brake light switch... 3 switches later and 2 code clearings, still flashing. Brake lights work fine. All wiring reads fine. Goll dang german wiring. (actually, made in mexico....)

I'm thinking it could be that my brake light bulbs are all burnt out; that would explain why people have been flashing their brights at my rear for the past little while.

If that doesn't fix it, I have a new brake light switch on hand (though again, there's no code), and after that I'll look into Relay 109.

I got this light flashing on 2 occasions:

-When I replaced the brake lights bulbs by LEDs.

-The first week after I installed an upgraded ECU (along with a CEL). Both have disappeared now. But I know the brake light switch recall haven't been serviced yet on my car, gotta get an appointment for this.

17970 - Quantity Adjuster (N146): Upper Limit Reached
P1562 - 35-10 - - - Intermittent

Will also cause the light to flash.

PROBLEM SOLVED!

Replaced the brake lights with new bulbs, and the glow plug light ceased its flashing.

I turned up my Bully Dog box to the max and after the tailpipe smoke cleared I saw the flashing glow plug light.
The car reved up very quickly then cut out at 3000ish rpm only to pick it up hard again when the revs dropped back down to 1000ish, only to cut out again.
She was smoking like a tractor puller for a few seconds, yikes.

Is over boost a reason to flash the GP light?

Jeece said:

I got this light flashing on 2 occasions:

-When I replaced the brake lights bulbs by LEDs.

Click to expand...

Ok.. I just did that and now have the GP light flashing. I know my lights work just fine and my cruse did as well. I take it it's just the low current draw of the LED bulbs thats confusing the ECU and causing it to do this? I really don't want to have to stick resistors in, kinda defeats the whole point of going LED. I own a VAG cable, is there any way to make it ignore the brake lights, so as not to flash the GP light any more?

Also sorry for the necro bump.

Tuning boxes will cause the flashing glow plug light when turned up to high. Had the same problem with my 99.5 golf with the diesel power box. Just turned it down and the problem went away, easy fix.

Another Solution: Fuses

If your brake lights don't work, and your glow plug dash light is flashing check:
1. The bulbs - top ones - (which you've probably already done)
2. The fuses in the side panel (#13 particularly)
3. The brake light switch above your brake pedal.
All of these are easy, inexpensive fixes that require NO TOOLS. (Although if you need to replace the brake light switch it is easiest if you remove the lower dash panel with the aid of a small star key.)
Don't pay the stealers $100 for a diagnostic unless you've exhausted all possible options.

Due to not always being able to find this Thread, I copied and pasted MOGolf's list many moons ago. I've also pasted that list in Posts giving him credit.

Good work MOGolf!

Thanks Mo, this is the gift that keeps on giving.

I seem to have gotten very lucky. In the process of trying to remove my dash cover to get at the brake switch, I thought what if... and found that just the rear brake light fuse was blown!!!! I would have thought VW would have been a little more clear on lights being blown. My code reader did not pick up any P codes either, but I wonder if that was because the fuse was blown, not a bulb.

My older VW's say if the glow plug light blinks, it is water, and drain it off. The older cars even came with a bag and hose! I pulled over right away, checked the manual on the 2005, and all it said was "go to a dealer right away". When I got home, I drained the filter under the hood right empty, but the flashing light did not go away.
I checked out the rear bulbs, and not it either. (ps , it turns out that you have to remove that side bulb with the long extension first, before you break the tab )

Also, I just blew one of the front day time light bulbs, and no lights on the display! wierd eh?

bonothoe said:

If your brake lights don't work, and your glow plug dash light is flashing check:
1. The bulbs - top ones - (which you've probably already done)
2. The fuses in the side panel (#13 particularly)
3. The brake light switch above your brake pedal.
All of these are easy, inexpensive fixes that require NO TOOLS. (Although if you need to replace the brake light switch it is easiest if you remove the lower dash panel with the aid of a small star key.)
Don't pay the stealers $100 for a diagnostic unless you've exhausted all possible options.

Click to expand...

I started my Golf after stopping at the shop for a brief moment. Turned they key and car wouldn't start. So I tried again and after a few turns still no luck....did press the accelerator a few times but still no luck. Tried her again and she started with 1st attempt. Drove off and then the glow plug light started flashing, stopped the car, switched her off, waited a few seconds and started her again....same problem....flashing glow plug light. Drove home slowly....luckily 2km away. Read on a few threads to check the brake light switch and possible faulty bulbs. The brake lights work fine, no dead bulbs. I allowed the car to stand for about 2 hours, started her again and soon after idling for a few seconds, the light started flashing again. Started her this morning....no change.
I gather the only solution is to have her checked for error codes?

Can one damage the vehicle by driving her like this? Which of the errors/faults can be the worst scenario?

PJVWGolf said:

I started my Golf after stopping at the shop for a brief moment. Turned they key and car wouldn't start. So I tried again and after a few turns still no luck....did press the accelerator a few times but still no luck. Tried her again and she started with 1st attempt. Drove off and then the glow plug light started flashing, stopped the car, switched her off, waited a few seconds and started her again....same problem....flashing glow plug light. Drove home slowly....luckily 2km away. Read on a few threads to check the brake light switch and possible faulty bulbs. The brake lights work fine, no dead bulbs. I allowed the car to stand for about 2 hours, started her again and soon after idling for a few seconds, the light started flashing again. Started her this morning....no change.
I gather the only solution is to have her checked for error codes?

Can one damage the vehicle by driving her like this? Which of the errors/faults can be the worst scenario?

Click to expand...

Yes, you should pull the codes to see what exactly is causing the light.

As for damage, if certain sensors fail the ECU will substitute a generic value or use info from another sensor.
For example, if the engine speed sensor fails, the ECU will use the needle lift sensor info as a substitute. If the needle lift sensor also fails, then the engine shuts down.
So, if the engine is running, it may not be running at optimal settings but the engine is unlikely to explode immediately. I would want to get the codes pulled as soon as possible, though, so I could get the problem solved.

Old thread, but wanted add that mine started flashing after I put in LED replacement brake light bulbs.

tfbiii said:

Old thread, but wanted add that mine started flashing after I put in LED replacement brake light bulbs.

Click to expand...

Yeah, the circuit needs a clean (my term) electrical connection through a bulb filament in order to satisfy the ECU. For my ALH engine in the Vanagon, I mounted a separate bulb under the back seat (that's the nutshell story).

So, I suppose if you are good with wiring, you could tap into the circuit for
the brake light at or near the assembly on the left or right and mount a single bulb somewhere in trunk. That would give the ECU the info it is looking for.

The center light above the back window is not monitored. So, stay away from that circuit.

Would this also be fixed with LED bulbs that are "CANBUS" compatible?

tfbiii said:

Would this also be fixed with LED bulbs that are "CANBUS" compatible?

Click to expand...

To confirm CAN Bus compatibility, in the link below, scroll down until you find the paragraph about Bulb-Out..... I think you will find the answer there.

Note: This is a good read for those who have scratched there head about CAN BUS ....

https://www.superbrightleds.com/blog/can-bus-led-bulbs/293/

So my 2002 TDI Automatic has a flashing glow plug light. It is not in limp mode and break lights work, not sure what do I do next?

Scan it

This happened to me today after I changed the battery. Any ideas?

Scrap it

GUYS GUYS GUYS!!....I think it kinda makes sense now....My VW T5 carravelle was in for service yesterday and came back and was just fine....drove home about 50KM and in stop and go traffic....no problems....got home and replaced five the front globes on the headlights with generic H7 bulbs....wanted to go out at night....then BOOM....glowplug light flashing no reving...straight into limp mode....so the threads ive been reading seems like people were changing some bulb somewhere then issues with the GP started....dont you guys think this is odd? or related ?....and whats the solution?