P2181 Code/No Heat

[tsk]

My daughter's car has started throwing a check engine light P2181 and it has no heat (or relatively no heat). It heats up to temp (it seemed a bit slow to me but it does hit half way and stay there). I recently replaced the coolant overflow tank (and whatever sensor is in there) after the light came on. The old one was cracked but aside from that it did nothing.

I'm assuming the thermostat and water pump are fine because I'm not overheating? Can anyone help me pinpoint the issue? It sounds like there are a few possibilities but my searching never showed this code + no heat. I'll mention I didn't bleed it after swapping the overflow tank but I doubt there's enough air to have almost no heat.

I do have all the parts for a timing belt change (including water pump and thermostat) which I'll get to doing eventually but I don't know that I'll have time for those now unless I need to got that deep.

Thanks in advance.

[customa4]

Here's some info on that code. Click The plug that goes into the coolant reservoir itself is the coolant level sensor. Do you have access to VCDS? You can monitor the engine temps to see if the coolant temp sensors are functioning correctly.

Here's some good info on testing

For under $20 you can easily determine if the problem is the CTS or the thermostat. Clicky click. and after you figure that problem out I can assure you that you will find numerous other uses for the scanner.

for reference: If your thermostat is functioning properly you should see temperatures at idle in the 220° to 230° range on the coolant return hard pipe as it leaves the rear coolant flange and flows toward the upper radiator hose. If it consistently goes much below 200° you probably need a new thermostat.

I plan to follow this procedure on the t-stat.

Possible Solutions:

Check Coolant Thermostat
* Use Graph function in VCDS, Measuring Value Blocks - MVB
* S tart Engine cold, graph Coolant Temperature Sender (G62) Typically MVB Group-001
* Hold RPM around 1,500rpm and watch coolant temp increase in Graph until thermostat opens, indicated by a slight drop in coolant temp
* If coolant temp drops below minimum operating temperature (80°C) or never reaches operating temperature, (verified by external thermometer) suspect failed thermostat

Vehicles with both G62-Engine Outlet, Coolant Temperature Sensor and G83-Radiator Outlet, Coolant Temperature Sensor
* Use Measuring Value Block group MVB-130 instead on MVB-001
* G62 should increase in Temperature before G83 increase when engine coolant is cold
* G83 will increase when the thermostat opens and after G62 reaches operating temperature (80°C)
* If G62 and G83 both increase while engine warms up, suspect failed thermostat

Special Notes
Check the stored Freeze Frame data with this fault code. Freeze Frame information will be found in the fault code description (if the module supports it) or in Generic OBD-II if the vehicle complies with those regulations.
Freeze Frame data stored at -40*C is generally an indication of a faulty ECT or wiring.
Freeze Frame data stored at +140*C is generally an indication of a faulty ECT or wiring.
Freeze Frame data stored with in the 68*C ~ 80*C range is an indication that the vehicle was close to, but not within, the cooling systems normal operation range. The Thermostat itself or Cooling system components may be at fault.

You got it! To put all that test data in simpler terms:

When you first start the engine the thermostat is closed. The water pump circulates the coolant through the "small loop". Colant goes through the block and out of the rear coolant flange where the upper G62 sensor is located. from there is distributes to the heater core and then back to the thermostat housing through the lower return hard pipe.

Coolant also circulates from the rear flange into the upper coolant return hard pipe. The upper hard pipe has several drops in addition to supplying the radiator. The first drop flows through the oil cooler, connects to the lower hard pipe and ultimately empties into the t-stat housing. The second drop goes directly to the thermostat housing.

The drop from the upper hard pipe and the lower hard pipe both flow across the bellows side of the t-stat which happens to be located the block side of the thermostat housing. Consequently the coolant can flow freely across the t-stat bellows and get sucked back into the block by the water pump. The coolant will continue to circulate through the small loop until the bellows gets hot enough to open the thermostat.

Once the thermostat opens coolant can be pulled through the lower radiator hose (where the lower G83 temperature sensor is located). This is called the large loop and it incorporates flow from the upper return hard pipe →upper radiator supply hose→radiator→lower radiator return hose→thermostat housing→back into the block.

So logically the lower G83 sensor should remain at a low temperature until the t-stat starts to open. The G62 sensor will heat up even before the t-stat since it is on the out-feed side of the block. If both sensors heat up at the same rate it would indicate that coolant is flowing through the large loop at the same time as it is flowing through the small loop. Obviously this could not happen if the t-stat was closed.

Hope that all helps to make sense out of what you are monitoring.

And good luck!

This info is from this thread. Click

Here's one more thread where the person had the same malfunction code as you and the problem ended up being the thermostat. Click

Sorry, don't mean to bombard you with a ton of links but I guarantee you if you read it you will figure out the problem.

[tsk]

Thanks, I have an IR sensor so I'll give that a check. Let me ask a quick question: how bad is the thermostat. I did it on a 3.0 in the past when I was doing the timing belt. That seemed like a royal pain if I wasn't already doing the timing belt. Is the 1.8 as bad? If it was fairly easy I'd just go toss a new thermostat in there but looking at the writeup, sounds like a lot of steps.

I do not have VCDS fwiw.

[customa4]

No, it's really not that bad at all. If it does turn out to be your thermostat, make sure you change the j-plug right on the side of it. Here's a write up on the thermostat replacement. Click

Here's a video.



Not sure how familiar you are with releasing the electrical connectors on these cars. Here's a video to save you the hassle if you haven't messed with them before.

[tsk]

I'm quite familiar with busting the suckers so a proper method is very helpful. Thanks.

[customa4]

It's possible to just pull that tab back with your thumb without actually needing to use a screwdriver to open it up. Same concept where the lever just kinda pulls back but you could use your thumb instead.

[tsk]

Just to add an update for anyone who searches for this problem in the future. I'm not exactly sure what the problem on this was because things took a turn for the worse but I am fairly certain the thermostat was involved. The top of the thermostat housing showed signs of being cracked. When I got it off, it was fully cracked but it was obvious the housing was cracked before I had worked on it because there was dried crusty coolant on it. I'm suspicious that the water pump may have been involved as well because while waiting for the j-plug to arrive my timing belt went, but that's the subject of another thread.