Error Code P050C is defined as Cold Start Engine Coolant Temperature Performance. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. It typically applies but not limited to vehicles from BMW, Dodge, Ford, Jaguar, Jeep, Land Rover, Mazda, Mitsubishi, Toyota, and Volkswagen. Specification of the definition, troubleshooting, and repairs, of course, vary from one make/and or model to another.

When this code is stored, that means the PCM has determined a problem with the vehicle’s engine coolant temperature performance. The ‘Cold Start’ is a term used engine drivability implemented only when the engine is at (or lower) than ambient temperature.

The PCM (powertrain control module, also known as ECM or engine control module) monitors the ECT (engine coolant temperature) through one or more ECT sensors. These sensors house thermal resistors brass (or plastic) housing. The housing is designed so that it may be threaded into the engine block, cylinder head, or intake manifold; where the engine cooling passages are located. When the thermostat opens, the coolant flows across the tip of the ECT sensor (where the thermal resistor is). The ECT sensor is provided a reference voltage and a ground, but the sensor completes the circuit.

As the temperature of the ECT sensor increases, the resistance of the thermal resistor decrease, which results into higher voltage being sent to the PCM, and vice versa when the temperature of the engine coolant decreases. The PCM receives these variations in circuit voltage as changes in coolant temperature.

Some vehicle makes and models use multiple ECT sensors, which is commonly found in one of the radiator tanks. The PCM compares input signals between ECT sensors to determine whether or not the engine coolant is efficiently flowing.

In most cases, the ECT is also compared to the ambient temperature during cold start conditions. Vehicles are equipped with an ambient temperature sensor which works similarly to the ECT sensor and is normally found near the grille.

When the PCM starts to see a discrepancy between the ECT and the ambient temperature sensors that exceed its threshold, under cold start conditions, then the Error Code P050C will be stored, while simultaneously activating the Check Engine light. For some vehicles, multiple failure cycles may be required for the Check Engine light to illuminate.

Common Symptoms

As with other error codes, this code registers to the vehicle’s memory system and illuminate the Check Engine light. Other common symptoms of this code include:

  • Drivability issues during cold start
  • Rich exhaust
  • No heat inside the passenger compartment

Other ECT sensor related codes may be present.

Possible Causes

  • Faulty primary or secondary ECT sensor
  • Shorted or open circuits or connectors
  • Defective ambient temperature sensor
  • Damaged thermostat
  • Low engine coolant

How to Check

If there are other ECT related codes present aside from the P050C, then it’s important to address those codes first before attempting to diagnose and repair the latter.

Start your diagnosis by checking the engine coolant level and not overheating. If everything is okay, then proceed with a visual inspection of the ECT sensor system connectors and wiring.

To diagnose this code, you need to have a reliable vehicle information source, infrared thermometer, laser pointer, diagnostic scanner, and a DVOM (digital volt ohm/meter).

You will also need diagnostic flow charts, connector face views, connector pin-out charts, wiring diagrams, and a component testing procedures and specifications to diagnose the code accurately. All these information can be found in your vehicle information source.

Next up, connect the scanner to the vehicle diagnostic port. Retrieve all stored codes and freeze frame data and write them down. Clear the codes to see if the code comes back.

If the code reset, turn the key on with engine off (KOEO) and then reconnect the scanner. Then, check the actual coolant temperature at the right spot near the ECT sensor using the infrared thermometer. Observe ECT data on the scanner and see if include only pertinent items for faster and more accurate data response. If the ECT displayed on the scanner fails to match actual coolant temperature, follow the diagnostic steps below.

If some crazy ECT is displayed on the scanner data display (like -38 degrees):

  • Test ECT reference voltage and ground (still with KOEO)
  • Unplug the ECT sensor connector
  • Use the positive test lead of the DVOM to probe the reference circuit
  • The negative test lead should be used to probe the ground circuit of the same connector
  • The DVOM display should reflect reference voltage (usually 5-volts)

How to Fix

  • Make sure engine coolant level is full, add or fill as needed
  • Repair or replace shorted or open circuits or connectors
  • Replace primary or secondary ECT sensor
  • Replace ambient temperature sensor
  • Replace damaged thermostat


You can use the DVOM to test the individual coolant and ambient air sensor, refer to the specifications and testing procedures set by the manufacturer. Sensors that don’t coincide with the specs should be considered defective.

Use the TSB (technical service bulletin) for your vehicle. Many times manufacturers provide the proper diagnosis and repairs for the problem.