No heat / auxiliary pump issues

[white_shark]

Hi all, maybe the issue I'm having will be useful to someone else as I've seen lots of threads about heating issues here but nothing mentioned the auxiliary pump faults.

So the problem goes as follows. It's a A4 B9 avant 35 tfsi, 19 reg - bought it about 3 weeks ago from a dealership with less than 8k on the clock.

I start the engine when the car is cold, everything heats up properly, coolant temp reaches 90 degrees and stays put no matter how fast I go/what revs, all good. Heater is working, fans, everything. Coolant level is between min and max. So basically no issues at all.

But once I stop the engine and start it again (assuming there's some residual heat), no heat in the cabin anymore. Fans are spinning, temperature is fine, even the radiator fun is spinning but no heat.

I touched the hoses everywhere to find the (possibly) faulty item and here it is, I suspect, an auxiliary water pump. The incoming hose is hot and the outgoing one, which goes to the cabin radiator, is cold. The item number is 06H-121-691-N.

I am not exactly sure if it is the only faulty item, if the failure is hardware or software, or whether it's the root cause. 

 

Has anyone had/heard of something similar? Any advice is highly appreciated since I am now waiting for the reply from the dealership and how they suggest to deal with it.

 

[white_shark]

A few updates.

1. The car stood for a while and then the cold temperatures kicked in. Heating stopped working altogether, no matter cold or hot engine.
2. Coolant was at MIN level when the car was cold so I topped it up to MAX. Heating started working again while the engine is not fully warmed up.
3. I thought that fault was with the G83 temp sensor (in the radiator's bottom hose), which apparently controls the aux water pump and the auto start-stop because both don't work.
4. But it turns out, the bottom radiator hose is cold on the hot engine, which means it's the thermostat that's faulty.

Quite disappointed that a 3 year old car with less than 10k on the clock already has such a trivial yet annoying fault.

Will bring it to the dealership and try to fix this as well as do the full flush and cleaning of the cooling system. Hopefully it is covered under the approved audi warranty, otherwise will find an independent garage.

Edited January 19, 2023 by white_shark

[Steve Q]

The fault definitely is annoying, and shouldn't be happening. Please keep us posted on how you get on at the dealers. 

[white_shark]

Thank you Steve, will do.

I am bringing the car to an indie shop tomorrow and to the Audi dealership on Monday so will keep you posted.

Cheers!

[white_shark]

Tonight was about 5-6 degrees here in London and the heater worked just fine. Started blowing heat at about the second mark of the main coolant temperature display and kept doing so even after I stopped the engine for a while and then started it again. 

Now I am hoping that the diagnostics's gonna show something at least or it will remain a completely mystery. Perhaps some temperature sensor isn't working, which stops heater from working when it's cold outside. Or it was indeed an air lock in the cooling system.

[Steve Q]

9 hours ago, white_shark said:

Tonight was about 5-6 degrees here in London and the heater worked just fine. Started blowing heat at about the second mark of the main coolant temperature display and kept doing so even after I stopped the engine for a while and then started it again. 

Now I am hoping that the diagnostics's gonna show something at least or it will remain a completely mystery. Perhaps some temperature sensor isn't working, which stops heater from working when it's cold outside. Or it was indeed an air lock in the cooling system.

Could definitely be a sensor. If it's hit or miss then it definitely could be electrical. 

[white_shark]

An update as I visited an indie shop nearby and an official Audi dealership.

The local mechanics had discovered it was the coolant shut-off valve 4H0 121 671D. A simple solenoid, which intermittently gets stuck in a semi-closed or fully closed position. As I understood the schematics, this valve is preventing the (cold) coolant from circulating through the heater to make the engine warm up faster. According to multiple other forums' threads, it is very often stuck but many times in the open position, which of course goes unnoticed by owners. The worst is when an older revision part (B at the end) starts leaking and pushing coolant through the socket onto the wires, but this didn't happen in my case. All electrics is intact.

Diagnostics (and temporary fix) are fairly simple: knock on it with something chunky such as a screwdriver handle a few times and observe the heat coming back.

Importantly, it wouldn't show in the errors (unless the electrics is damaged and the circuit is always open/short) because there's no flow sensor and the device itself is passive. The only error related to the AC/heater I had was B108C07 related to the motor controlling the left air flap. And I am very glad I went to an indie shop first because I suspect the dealership, even if things were covered by the warranty, would do unnecessary replacements of the heater core, pump, thermostat, etc eventually damaging the system's integrity. 

To me, it was very confusing because it really reminded of a possible airlock, especially since there was a correlation between me adding coolant/revving up the engine and the heater getting back to life. Perhaps a stronger coolant flow would indeed push the valve into its place, who knows. The aux pump mentioned in the first message was suspicious too because of the outgoing hose being cold, but this was probably due to the closed valve, which also makes sense in retrospect.

Anyways, the dealership are now requesting if the replacement is covered by the warranty and will fix it, including flushing and re-filling the entire cooling system. I am a bit skeptical about the latter but I guess it's ok as soon as they know what they're doing.

 

Edited January 23, 2023 by white_shark

[fat al]

I have a similar issue with a 2.0 tdi and suspect the solenoid or the electric coolant pump may be to blame. What's the physical location of the solenoid?

[white_shark]

1 hour ago, fat al said:

I have a similar issue with a 2.0 tdi and suspect the solenoid or the electric coolant pump may be to blame. What's the physical location of the solenoid?

Hey Al, it's under the bonnet on the passenger side near the washer blades. There's a compartment with a plastic lid, and the valve is there.

[white_shark]

So the issue was resolved by the official Audi dealership under the "approved used" warranty for free. It was the coolant shut-off valve indeed, and they changed the coolant in the system as well.

 

Edited January 30, 2023 by white_shark

[fat al]

Thanks. Mine is out of warranty; it is with an independent mechanic who reckons the electric water pump is misbehaving. Nothing showing in scans though...

[white_shark]

2 minutes ago, fat al said:

Thanks. Mine is out of warranty; it is with an independent mechanic who reckons the electric water pump is misbehaving. Nothing showing in scans though...

If you trust them then it makes sense to replace the pump. Although I don't fully understand whether it affects anything at all when the engine is running at high revs. As I understand its purpose, it's supposed to help coolant circulate when the engine is idling or shut down. But I may be wrong.

As to scanning, not sure about the pump but the valve is a simple on/off device without any sensors. So as long as the current is flowing through it (no matter is it stuck or not), the car will think it's ok. Perhaps the same applies to the pump but again, all this is a pure speculation and I don't know for sure.

Good luck!

[fat al]

I don't think they are totally confident that the pump is definitely the issue, but they think it is the most likely candidate. They've offered to replace it for cost of parts and only charge labour if the repair doesn't solve the issue which seems to show willing - but it's still nearly £200 for the part.

Opinions differ about whether there is a coolant divert valve. It seems some TDIs have them, others don't, and they are not all in the same place.

I'd expect it to have thrown an error in scans if the pump was not working right. And for the car to be totally cold - it's running with some warmth, but not as much as it should have... I'll update if I/they find a solution.

[white_shark]

Well, you may try to easily check the valve. Just knock on it with something moderately heavy when the car is warm but there's no heat.

This is a very common issue when they get stuck due to purely mechanical reasons, so this either helps and you're getting hot air in a few seconds or not. If not, then perhaps it is the pump or something else, from lack of coolant to a leaking head gasket but hopefully it won't be anything serious.

As to whether a diesel has it, I don't know.

 

[fat al]

Thanks for the advice. There is not a valve with the position/function in this car. With the 2.0 TDI it is apparently only part of the system if there is an auxiliary diesel heater fitted.

The change of pump did not fix the problem. Can't help feeling that the mechanic should have seen that the old one was functioning fine from the diagnostics - which (having got the car back and been able to check for myself) it turns out do show data for it...

Next step will be to flush the heater core and, if that does not work, to drain all the coolant, flush the whole system and replace the heater core. Feeling the hoses shows there is good hot supply to the heater core but a significantly cooler return which makes me suspect poor coolant flow through the heater core.

[vrt]

I had recently come a cross the same issue with no heating also stop start was not working.

So the main pump solenoid connecter was loose re clipped it on and it made no difference so I punched a new aux pump located in the bumper access under passenger's wheel arch from euro part there was an option of the pierburg or a cheaper airtex. 

For the purpase of elimination. I purchased the cheeper on which was smaller so I used heat resistant pluming foam for packing, the wiring clip and the pipe locations where in the same place so a good match and reatached with the same bracket.

The results where not instantly noticeable but after around 50 miles  worked better stop start started working agane and after around 200 miles is working normally. 

Hope this helps other just to note it had already been to a garage and there hanted to have it for 5 days removing the dash and heating system. 

 

[fat al]

On 2/4/2023 at 10:15 AM, fat al said:

Next step will be to flush the heater core and, if that does not work, to drain all the coolant, flush the whole system and replace the heater core. Feeling the hoses shows there is good hot supply to the heater core but a significantly cooler return which makes me suspect poor coolant flow through the heater core.

Updating because there was a new reply. On my car the heater core was full of some sort of silty scale. Flushed it with fresh water, then radiator cleaner and it worked much better. I might have had to do this more than once, I think the problem recurred (it was a few months ago and I don't remember perfectly). Heater output is comfortable, though possibly not as hot as it should be - so it's possible the core isn't fully clean and needs replacing to work perfectly. It's unclear what caused (or is causing) the scale, presumably something before my ownership of the car. The whole system has been flushed and refilled with the right coolant since I bought the car so hopefully there isn't more scale developing.