P2181 Error code. Help me narrow this down

[Aveoon]

Check engine light came on the other day so I decided to scan the car with the ross tech vag com. Came up with this DTC:

Address 01: Engine Labels: 06B-909-518-AMB.lbl
Part No SW: 8E0 909 518 AK HW: 8E0 909 018 A
Component: 1.8L R4/5VT G 0004
Coding: 0016711
Shop #: WSC 12849 539 435846
VCID: 79F7EF2333C24D6

1 Fault Found:
18613 - Performance Malfunction in Cooling System
P2181 - 008 - - MIL ON
Readiness: 0000 0000


Seems like it could either be the thermostat or the engine temperature sensor located behind the block.

I'm driving a 2004 A4 1.8t quattro manual. I replaced the coolant temperature sensor that's connected to the radiator hose a while ago, that solved the first engine light that came on at the time. Then now this came on. What do you think?


Also, I checked the fans, they are both working. Ontop of that the heat is working just fine too. The temperature gauge gets up to normal temp within a normal time as well. The normal cold start does not work anymore (starts around 1300 rpm) and the fans seems to be running a bit high. Thoughts?

[old guy]

Your start up idle speed may be normal. You didn't give the parameters around the starting conditions. Here is a little more info on start up idle speed: Clicky click

Comments on your P2181:
I would start with replacing your rear CTS. Here's my logic behind the recommendation. Code P2181 indicates a problem with the performance of the cooling system. So one of two things is occurring. Either you actually do have a performance issue (faulty thermostat) or your ECM just thinks you have a problem based on feedback from the two coolant temperature sensors. The ECM monitors the temperature of the coolant leaving the radiator via the lower CTS and calculates the expected temperature of the coolant leaving the block as measured by the rear CTS by utilizing predetermined maps. It considers things such as engine load and the MAF volume to calculate the expected heat load. If the actual heat load is outside of the expected range you will get a P2181.

You indicated that your motor seems to be heating up normally and your heater is working as it should. That's a pretty good indication that your thermostat is functioning properly. So that leave the possibility that your ECM is getting false information from one or the other CTS. You indicated that you replaced your lower (radiator outflow) CTS so that leaves the rear (block outflow) sensor that is probably causing your P2181.

Good luck!

[bman005]

Find your freeze frame data. If the fault occurred between 65-79 degrees C then it is most likely a thermostat issue. Or you could simply drive down the highway monitoring your coolant temp. Once you reach normal temp take a drive on the highway and monitor, it should not go below 80 while cruising. If it does its your thermostat.

[Aveoon]

Your start up idle speed may be normal. You didn't give the parameters around the starting conditions. Here is a little more info on start up idle speed: Clicky click

Comments on your P2181:
I would start with replacing your rear CTS. Here's my logic behind the recommendation. Code P2181 indicates a problem with the performance of the cooling system. So one of two things is occurring. Either you actually do have a performance issue (faulty thermostat) or your ECM just thinks you have a problem based on feedback from the two coolant temperature sensors. The ECM monitors the temperature of the coolant leaving the radiator via the lower CTS and calculates the expected temperature of the coolant leaving the block as measured by the rear CTS by utilizing predetermined maps. It considers things such as engine load and the MAF volume to calculate the expected heat load. If the actual heat load is outside of the expected range you will get a P2181.

You indicated that your motor seems to be heating up normally and your heater is working as it should. That's a pretty good indication that your thermostat is functioning properly. So that leave the possibility that your ECM is getting false information from one or the other CTS. You indicated that you replaced your lower (radiator outflow) CTS so that leaves the rear (block outflow) sensor that is probably causing your P2181.

Good luck!

Excellent diagnostics. That's what I was figuring due to all the other parameters. I had no idea that the cold start depends on things such as the dew point. I should do a bit more reading on that. =D I'll try replacing the rear CTS and see how that goes. Once I do I'll report back. Thanks man!