Coolant and Heating flashing red light on dash

Basic operation.

The light will flash when you start your engine for a few seconds this is normal. It should then go out and stay out unless either your coolant level is low or your van is over heating. However there are several other faults that can make it come on incorrectly. A quick check whilst you are driving is to put the heating on if you have heat coming up front then you most likely still have coolant going around the system. Look in the rear view mirror for steam! More often than not it is due to the level sensor in your header tank has become gunged up and is incorrectly thinking that your header tank is empty. Remove the two pronged sensor from the tank and give the prongs a clean

syncrosimon

There are two other causes for that little light to blink that I have experienced. 1. An electrical short circuit. This happened to me when an ill fitting battery was shorting on the battery lid. The red light would flash intemitently and the temp gauge increase in temp very quickly whilst shorting. 2. The main wiring harness multi pin connector to the dash pod comes a little loose. on later models this can also sound the buzzer of doom when nothing else is wrong, but should also effect other dash led's by making them not work. A gentle wiggle should correct, on my lhd you can reach this plug from the driving seat by sticking your hand up underneath, i cant remember if this is the same on a rhd.

Hope this may be of help as it is not always the obvious.

The engine wont be overheating if the needle doesn't say it is. The fan should come on when the needle is a needles width to the right of the little red light. (assuming that the gauge is working) The temp needle should start fully to the cold left side, then rise over about 4 miles to the middle, where in normal conditions it stays rock steady. Ticking over for long periods will require fan action such as in your traffic jam to cool the engine, but should be shown in a slight rise in the needle position. When the fan comes on you should be able to see the needle drop, a gentle rev to get the coolant flowing round faster at that point will cool the engine down faster. or you can put your heater on full for a time. This will keep the engine cool even if your main fan isn't working

Mocki

you need to remember that the light takes its signal from the temp sender for over heating, AND from the level sender in the headertank for low coolant, the rad fan is connected to neither of these and has a seperate sender switch in the rad itself, so is totally independent...

also check connections in the electrics box in the engine bay, where there is yet another junction for the gauge and the red light of confusion.....

Header tank cap check

just something to check with the cap screwed tight on the bottle when the coolant is cold blow/suck on the take off pipe. you should not be able to blow into the system or suck out. if you can your cap is faulty it needs to seal so the coolant can pressurise and not boil! non sealing will cause fluid loss and so can cause the fault you have with no apparent coolant loss!

by AngeloEvs

Almost right, firstly the chips in the Level Sender Control Unit (LSCU relay 43, on the main fuse panel at the front on late vans but up under the dash on the A pillar near the crown of earths on early vans) )are VAG coded so no idea of what they are. The gauge has its own internal circuit that flashes the LED for a few seconds (the Self Test). This circuit will be triggered whenever the resistance across the gauge falls below 50 ohms and this is the coolant senders resistance when the coolant exceeds normal operating temperature. The sole function of the LSCU is to monitor fluid level and to trigger the gauges internal circuit in the event of coolant loss. The LSCU sends a low frequency AC pulse to the probes in the header tank (probably to prevent electrolysis and degrading the probes hence the AC). If the pulse waveform alters due to no coolant being present then the LSCU sends a series of short duration low frequency negative pulses to the temperature gauge. These pulses are seen by the gauge as temporary short circuits across the gauge and the internal gauge circuit responds by activating the LED. The reason for sending short duration pulses 'once every few seconds' to the gauge is to prevent it from deviating from the current temperature position (otherwise it would swing hard over to the right). In the event of overheating, the internal circuit of the gauge will switch the LED off when coolant temperature returns to normal (sender resistance returns to a normal value greater than 50 ohms) but if the LSCU is activated it has to be reset by switching the ignition off. The reasoning for this is that whilst coolant temperature can return to normal coolant cannot replace itself and hence the continual flashing in the event of coolant loss and temporary flashing in the event of temporarily overheating. The problem with the LSCU is that it is easily triggered by sudden fluctuations in Voltage, poor earths and has a very narrow margin of error regarding the resistance of the coolant fluid - according to VAG service bulletin - antifreeze mixtures over 60% will cause flashing red light syndrome.

Removing the LSCU stopped the Led flashing so the fault is in the coolant level circuit, these are the usual suspects.

!. Coolant level Low? you prabably checked this and found its ok!

2. The LSCU Earth connection at the earth crown next to the fuse box.

3. The earth under the ignition coil. (or under the airfilter box on the engine wall on a diesel)

4. Poor connection at the coolant level socket.

Angelo EVS coolant warning light module testing The most important thing is to establish that the coolant level is correct and engine running within normal temp range when the LED is triggered. As stated, the VW Coolant LED can be triggered by low coolant or high temp and both have different wiring systems/components that are highly sensistive to poor connections and components. To establish wether the fault is in the Coolant temperature circuit or the coolant level warning circuit you need to do the following:-

1. Locate the module marked 43 (or 42) situated in the main fuse box under the glove compartment and make a note of its position.

2. When the LED starts flashing - park, switch engine off and remove the module.

3. Re-start engine, and observe LED for about 30 seconds or so. Continue with a short drive

If the LED continues to flash with the module removed the following need to be checked :- temperature issue due to low coolant, engine/timing, etc, an intermittent wiring fault in the temperature sender circuit, guage is not reading the correct temp, etc.

If the LED goes out after a few seconds and no longer flashes when driving with the module removed the fault is in the coolant Level warning system due to either of the following - low coolant level - faulty module 43 - poor earth connection - poor connection of the temp gauge centre nut to the ribbon cable - corroded prongs on the coolant level sender or poor connections to it.

Poor connections in the coolant level sytem wiring is a common problem. As Mocki points out there is an earth cnx in the engine bay and another located on a crown cluster next to the fuse box on the door pillar. Unfortunately, there are a whole bunch of earth spade terminals at the latter and best to check/clean them all. Even a poor battery earth, incorrect Anti-freeze mix can trigger the LED.

5. The LSCU itself

6. Loose nuts behind the temperature gauge.

Midlifecrisis

In response to a continually flashing light

So, a) if the led flashes with the relay removed then you can discount the coolant level probe and wiring to/from it as a culprit (because with the relay removed all of this is unconnected to the gauge)

b) if the led flashes on the 'known good' dash then you can discount any component of the dash/gauge as the culprit (because the two gauge behave the same)

c) the gauge needle works correctly so we can discount the temperature probe and the wiring from the temperature probe to the dash (because the gauge needle is being 'driven' correctly by the temperature probe as it is heated by the coolant)

(I think) that only leaves the ground wiring to the gauge pod??? Or possibly (but more unlikely) the 10volt supply to the gauge.