Diesel Glow Plug Control Problem - Error Code 626

Translated on 24-08-2026, 7:05.

Hello everyone!
"Can anyone give me a troubleshooting tip? In my 1998 626 GF diesel (74kW), the preheating control light starts flashing after some time of driving. Starting is normal: the light goes out after about 2 seconds, then it starts perfectly fine. Strangely, the warning light then starts blinking at different times during the drive. Usually, it happens when you have to stop for the first time after driving at a higher RPM and the engine is idling. However, once it starts flashing, it doesn't stop. After turning off and restarting, it starts again after some time."
All the spark plugs, the temperature sensor, the wiring/fuse, and the relay have been checked. Everything is okay. Additionally, Mazda stated that there are no error codes stored in the control unit either.
Does anyone have any ideas about this?
(Okay, since the car otherwise drives perfectly fine, one could remove the annoying warning light as a temporary solution, but that's not really the point.)
Best regards from Cologne,
Uli.

Translated on 24-08-2026, 7:07.

Could you please check the memory when the light is blinking? I suspect it's detecting some kind of error; it wouldn't be blinking for no reason. Could you also take a look at the LD control system? The problem might be hidden there.

Translated on 24-08-2026, 7:08.

Hello everyone!
It appears to be a problem related to the exhaust gas recirculation (EGR) system. After replacing the electronic control unit on top of the pneumatic valve control (position sensor?), the warning light initially went out. You can also see that the valve is working after starting the engine. Therefore, the vacuum hoses should be sealed.
After the car stood overnight, the warning light now immediately illuminates when the ignition is turned on (previously it only came on after driving for a while). Additionally, a noticeably loud "clack" sound can be heard when turning on the ignition. However, starting and driving still work perfectly fine (and fuel consumption and performance remain unchanged).
Greetings,
from the bewildered Uli