P2181 – Cooling system performance

By Jason (Contact Me)
Last Updated 2016-09-13
The Automotive Copywriter

Trouble Code	Fault Location	Probable Cause
P2181	Cooling system performance	Radiator, coolant thermostat, engine coolant blower motor, ECT sensor

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What Does Code P2181 Mean?

Your engine temperature is monitored in the cooling system whenever the engine is running and serves several purposes. When the engine is cold, the air/fuel mixture is more rich to allow for the engine to idle smoothly as it warms up. It detects low engine temperature that can affect the exhaust gas recirculation (EGR) efficiency. It also determines if the engine is running too hot, signaling a problem before the engine overheats. When the engine temperature reading changes at a rate beyond what the PCM considers normal operation, DTC P2181 is set in the powertrain control module and the Check Engine light is illuminated.

What are the common causes of code P2181 ?

Corrosion in ECT sensor connector
Poor connection at ECT sensor or PCM
Broken or damaged wiring
Thermostat stuck open or closed
Low engine coolant level
ECT sensor failure
Air in cooling system

What are the symptoms of code P2181 ?

Any one or a combination of the following symptoms can be present when DTC P2181 is set:

Hard starting when the engine is cold
Poor heat flowing through the dash vents
Rough idle when engine is warm
Temperature gauge reads full hot or no reading is displayed
Surging idle

How do you troubleshoot code P2181 ?

The engine cooling system is considerably more straightforward than other engine or electrical systems. Diagnosis can be completed with a few common tools that a capable home mechanic will probably already possess. You'll need a digital volt-ohmmeter (DVOM), a thermometer (infrared is best), and a scan tool to clear the codes when you're done. When you begin your diagnosis, consider if there have been any other repairs completed recently. Have you had a cooling system repair or a block heater installed? Has work been completed that required electrical connectors to be disconnected? If so, you might be able to forego in-depth diagnosis by first rechecking those items. Check for an airlock in the cooling system and proper coolant level. Top up the coolant to the proper level as indicated on your vehicle. Air sitting at the ECT sensor can cause an extreme reading that sets the DTC. If air is regularly being introduced into the cooling system without a known cause, it can be an indication of a serious issue like a head gasket leak. Because DTC P2181 indicates an unusual coolant temperature reading, start by identifying the coolant temperature at various common points on the engine. When the engine is cold, monitor various points under the hood with a thermometer. As the engine heats up, the thermostat inlet should be considerably colder than the lower radiator hose. If the engine takes a long time to warm up and there's little difference between the two temperatures, your thermostat is likely stuck open. When the engine is hot, check the radiator hoses for similar temperatures between the upper and lower hose. If there is a wide difference, check the temperature between the thermostat inlet and the lower rad hose. A major temperature variance tells you the thermostat is not opening. Either of these conditions require the thermostat to be replaced. If engine temperatures are normal as the engine is heating up, check the engine coolant temperature (ECT) sensor operation. With your DVOM set to ohms, check the resistance in the ECT sensor when the engine is cold -- that's when it's highest. As the engine warms up, the keep monitoring the ECT sensor resistance. It will drop at a steady rate as the engine gets warmer.

If the ECT sensor reads erratically as the engine is warming up, with resistance jumping high or low intermittently, the sensor needs to be replaced. If the sensor shows excessive resistance or none at all, replace the sensor for an internal fault.

Check the ECT sensor wiring for corrosion, breaks, or chafing. An intermittent P2181 code can be the result of an intermittent loss of signal due to a poor wiring connection. Test the wiring at the ECT sensor input for 5 volts. Check the sensor output circuit for continuity between the sensor and PCM. Repair any breaks or corrosion, then clear the codes. If there is no 5-volt power to the sensor and the circuit is proper, replace the PCM with a known good unit.

Codes Related to P2181

P2182 - Engine coolant temperature (ECT) sensor 2 - circuit malfunction
P2183 - Engine coolant temperature (ECT) sensor 2 - range/performance problem
P2184 - Engine coolant temperature (ECT) sensor 2 - circuit low
P2185 - Engine coolant temperature (ECT) sensor 2 - circuit high
P2186 - Engine coolant temperature (ECT) sensor 2 - circuit intermittent/erratic

BAT Team Discussions for P2181

2003 VW Passat 2.8L V-6
It has an auto trans, FWD, and had the CEL on for some time. The codes set were P2181, P0300, P0303, and P0304. I pulled the spark-plugs to inspect and check compression. The first thing I noticed is that the plugs are way down deep, and that "well" was very full of oil on #1, 3, 5, & 6. The fir...