Mercedes Benz

Okay, let's break down the **P0115 Engine Coolant Temperature (ECT) Sensor Circuit Malfunction** code. This OBD-II (On-Board Diagnostics) trouble code indicates a problem detected by the vehicle's computer (**Powertrain Control Module - PCM**) with the circuit supplying information about your engine's coolant temperature, specifically from the **engine coolant temperature sensor** located in the cylinder block of your engine. Here's what you need to know: ### What is happening? 1.  The ECT sensor monitors the temperature of your engine's cooling liquid (antifreeze/coolant). 2.  It sends this information (as a varying electrical signal) back to the PCM. 3.  When the PCM detects an abnormality in this signal – such as a voltage reading that doesn't make sense given typical operating conditions, or inconsistent readings across multiple sensors if equipped – it triggers the P0115 code. ### Common Causes *   **ECT Sensor Failure:** The most frequent cause is the sens...