Engine Running Colder than Normal
 

Hey Everyone,

I've been working on a 2007 Jetta 2.5L 5 cylinder that keeps running slightly colder than normal. When we first bought it the engine temp was always 190F but now the car runs at about 175F consistently. We have an engine code of P2181 and have replaced the coolant tempt sensor and also replaced the thermostat itself. Both parts are VW parts and after a day or so the code pops back on after a little driving. We have to get emissions done on the car and we can't have an engine code. What else causes the p2181 that could be potentially causing our car to be running cold?

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EOBD II Error Code: P2181

Fault Location:
Performance Malfunction in Cooling System - Intermittent

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.
Reduced Heater Output - Cold toes.
Incorrect Temperature Gauge Readings.
Increased Emissions.

Wiring/Connection(s).
Faulty Coolant Sensor.
Faulty Coolant Thermostat.
Note: This fault code sets when engine coolant temperature mapping is lower and out of expected range based on operating conditions of the engine.
For example: Engine warms up, thermostat opens and stays open, coolant temperature drops below normal operating range. The Engine Control Module (ECM) knows the coolant temperature should stay within 80.0...110.0 °C typically after warm up. Thus a drop in coolant temperature below normal operating temperature is not possible without a Malfunction in Cooling System.

Possible Solutions:
Check Engine Coolant Temperature Sender (G62).
Inspect wiring for Engine Coolant Temperature Sender (G62) (Coolant Migration, damage, corrosion, etc).
Check (if applicable) Engine Coolant Temperature Sensor on Radiator Outlet (G83), Coolant Temperature Sender.
Inspect wiring for Engine Coolant Temperature Sensor on Radiator Outlet (G83) (Coolant Migration, damage, corrosion, etc).
Check Coolant Thermostat.
Use VC-Scope in VCDS.
Measuring Value Blocks (MVB).
Start 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 temperature.
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 Engine Coolant Temperature Sender (G62), Coolant Temperature Sensor and Engine Coolant Temperature Sensor on Radiator Outlet (G83), Coolant Temperature Sensor.
Use Measuring Value Blocks (MVB) group MVB-130 instead on MVB-001.
Engine Coolant Temperature Sender (G62) should increase in Temperature before Engine Coolant Temperature Sensor on Radiator Outlet (G83) increase when engine coolant is cold.
Engine Coolant Temperature Sensor on Radiator Outlet (G83) will increase when the thermostat opens and after Engine Coolant Temperature Sender (G62) reaches operating temperature (80°C).
If Engine Coolant Temperature Sender (G62) and Engine Coolant Temperature Sensor on Radiator Outlet (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 Engine Coolant Temperature Sensor or wiring.
Freeze Frame data stored at +140*C is generally an indication of a faulty Engine Coolant Temperature Sensor 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.

As taken from my new EOBD II Fault Codes Software

You should take it somewhere and get some more data. Need to see some freeze frame data. If it is showing the temp is actually between 155-175, then the vehicle was close to operating temperature and you have a cooling system fault. Anything else will generally mean you have a faulty ECT or wiring issue.