MIL light is on...code P2181 I replaced Coolant & Thermostat...thinking of replacing Fuel Cap & CTS. Think i should replace fuelpump? The car has began to have a slight hesitation every now 7 then, when idling.

it could just mean that the electric connections are not making a good contact with what ever its touching,
and the voltage can not get through to what ever its feeding.
it might be best to replace the thermostat just to be on the safe side.

Potential Causes:
- Connector
- Defective Coolant Temperature Sensor (CTS) Wiring
- Defective Thermostat

Tests/procedures
1. Measure engine temperature and ensure it is getting up to proper operating temperature.
2. Connect a Volkswagen-compatible scan tool and monitor engine temperature on the scan tool. Compare to the actual engine temperature to determine if the coolant sensor is working correctly.

Typical is you are in a location where winter is kicking in, and with a stuck thermostat, your temperature of operating engine is triggering codes bases on ECU not sensing accurate conditions. Your ECU is probably not allowing car to start as it is sensing an overly rich fuel mixture which can impede cold starts in cold weather. Replace that thermostat, it is there for a reason and when not working, engines never warm up to proper operating temperature which triggers all sorts of codes.

Good luck
Asthma-Free-Home.com

PO121 : TP Sensor Performance = The PCM supplies 5V to the TP sensor(throttle position). The TP sensor is a variable resistor that drops the voltage to about 4 volts at WOT(wide open throttle) to less than 1 volt at closed throttle. Some TP sensors are adjustable. others have a learn procedure to determine closed throttle. PO171 Fuel Trim System Lean = In closed loop the PCM adjusts fuel delivery based on H2OS 1 readings and is indicated by long & short fuel trim values. If lean the PCM will add fuel (fuel trim above 0%) & if rich the PCM will reduce fuel(fuel trim below 0%) PO128 ECT Below Thermostat Regulating Temperature = possible failed thermostat, low or empty on coolant, Engine Coolant Temp Sensor, Poor connection/Harness/Wires, faulty PCM Connection. I think you hit the nail on the head , the ECT Sensor ( which is different than the temp sensor for the dash gauge)

If the check engine light is On the owner would have performed a scan on his car which would have given him some error code and the code will indicate that thermostat is faulty. Is the code p2181? if it is i think the thermostat is faulty and needs to be replaced.

Replace the ( CTS ) Coolant temperature Sensor. VW oe only...Been updated.

Check the bottle is full. Do not use coolant sealers in this engine! Fix the leak.

How old is the Coolant Temperature Sensor (CTS)? The CTS have been know to fail, don't rule it out. After that, there's the thermostat and possible water pump. The pump would be your last choice since you did not say it was over heating and the effort required to replacing it. Go with the sensor first, it is a 2 part sensor, and apparently the half sending signal to ECU isn't working correctly according to the ECU.

Replaced the sensor ($43 from my local VW dealer: ouch.) Once you the parts in hand, and the engine was cool enough, it takes all of two minutes (less time than it takes you to replace one of the windshield wiper's rubber; who designed that damn thing????). Then replace the Thermostat 190F and cleared the check engine light.

Good luck and this should solve your P2181 Issues.

Trouble Code: P2181

Cooling System Performance Malfunction
Possible Causes:


ECT sensor has failed ECT Sensor (on Radiator) has failed ECT sensor signal circuit is open (inspect wiring & connector) ECT sensor signal circuit is shorted Cooling system malfunction, or the thermostat is stuck Engine not operating at normal operating temperature EOT sensor is damaged or it has failed

Hi,first thing your cambelt and tensioner should have been replaced 13k miles ago,it would pay you to replace the water pump at the same time as they are known for impellor failure = cooling system fault=P2181 code,hope this helps.
Darren

Im actually going through the process of fixing this problem with my car. the P2181 is a performance cooling error, usually brought up by thermostat, radiator issues, or ECT sensor. You should narrow it down and check both radiator and thermostat to prevent later issues. If all is well go to your local autozone, pep boys, checkers..etc. and have them erase the DTC error. If you are looking for a more long term solution you can purchase many different software such as VAG-COM or any other software used to run test on vehicals. Be sure you know what you are doing though because messing with your cars computer can have long term effects that can be pricey.