OBD-II Code P2185: Understanding Engine Coolant Temperature Sensor 2 Circuit High Input

What Does OBD-II Code P2185 Really Mean?

The trouble code P2185, a generic powertrain code applicable to OBD-II compliant vehicles (1996-newer, including brands like VW, Ford, Dodge, and Chevrolet), signals an issue with the Engine Coolant Temperature (ECT) Sensor #2 Circuit High Input. While the code is generic, specific repair procedures can differ based on your vehicle’s make and model.

The Engine Coolant Temperature (ECT) sensor is a crucial component, acting as a thermistor installed within a coolant passage in the engine’s cylinder head. Its function is to measure the engine coolant temperature. This sensor operates on a principle of resistance: high resistance when coolant temperature is low, and decreasing resistance as the coolant temperature rises.

The Powertrain Control Module (PCM), the brain of your vehicle’s engine management system, provides a 5-volt reference signal and ground to the ECT sensor. By monitoring the voltage drop across the sensor, the PCM accurately determines the engine coolant temperature. Code P2185 is triggered when the PCM detects an abnormally high voltage signal from the ECT sensor #2 circuit. This often indicates the sensor is reporting a coolant temperature that is unrealistically low, especially after the engine has been running. Essentially, if the ECT sensor readings suggest the coolant is below freezing after the engine has been operating, or if the sensor’s resistance falls outside the expected range, the PCM interprets this as a circuit malfunction and sets the P2185 code.

Important Note: P2185 is closely related to code P0118. The key distinction is that P2185 specifically points to a problem within the #2 ECT sensor circuit. Vehicles that trigger P2185 are equipped with two ECT sensors. Therefore, it’s critical to correctly identify and diagnose the #2 ECT sensor circuit when troubleshooting.

Decoding the Symptoms of a P2185 Code

When your vehicle throws a P2185 code, you might observe several symptoms affecting engine performance and fuel efficiency:

• Significantly Reduced Fuel Economy: An incorrect coolant temperature reading can lead to the engine’s computer miscalculating fuel delivery, often resulting in excessive fuel consumption.
• Engine No-Start Condition: In some cases, a faulty ECT sensor signal can prevent the engine from starting altogether, as the PCM relies on this data for proper engine operation.
• Poor Engine Performance: The vehicle might start, but run erratically, characterized by black smoke from the exhaust, rough idling, and engine misfires. This is due to the incorrect air-fuel mixture caused by the faulty sensor reading.
• Malfunction Indicator Lamp (MIL) Illumination: The check engine light, or MIL, will typically illuminate on the dashboard to alert the driver to the detected problem.

Pinpointing the Causes of OBD-II Code P2185

Several potential issues can lead to a P2185 code. Here are the most common culprits:

• Poor Connection at the #2 ECT Sensor: Corrosion, loose wiring, or damage to the electrical connector at the ECT sensor can disrupt the signal and cause a false high input reading.
• Open Circuit in the Ground Wire: A break or open in the ground circuit wire between the #2 ECT sensor and the PCM can prevent proper grounding of the sensor, leading to inaccurate readings.
• Short Circuit in the Voltage Feed Wire: A short circuit in the voltage supply wire between the sensor and the PCM can cause an abnormally high voltage signal to be registered.
• Faulty PCM (Less Likely): While less frequent, a malfunctioning PCM itself could incorrectly interpret the sensor signal or have internal issues causing the code.
• Defective Temperature Sensor: The ECT sensor itself may be internally shorted or failing, resulting in incorrect resistance and voltage readings sent to the PCM.

Troubleshooting and Solutions for Code P2185

Follow these steps to diagnose and potentially resolve a P2185 code. Safety First: Always ensure the engine is cool before working on the coolant system or electrical components.

1. Initial Scan Tool Check: If you have access to an OBD-II scan tool, begin by reading the ECT sensor #2 reading. Does the temperature value seem plausible? If the reading appears normal, the issue might be intermittent.

2. “Wiggle” Test: With the scan tool still monitoring the ECT sensor reading, perform a “wiggle” test. Gently wiggle the sensor’s electrical connector and wiring harness. Observe the scan tool for any sudden drops or fluctuations in the temperature reading. Drop-outs during wiggling strongly suggest a bad connection.

3. Sensor Resistance Check: If the scan tool displays an illogical temperature (e.g., extremely low when the engine is warm), check the resistance of the ECT sensor itself using a multimeter. Compare the measured resistance to the manufacturer’s specifications for the sensor at the current temperature. If the resistance is out of specification, sensor replacement is necessary.

4. Circuit Jumper Test: If the sensor resistance is within specifications, disconnect the sensor connector. Using a fused jumper wire, carefully bridge the two terminals of the connector. Now, check the temperature reading on the scan tool. It should now indicate a maximum temperature, typically exceeding 250°F (121°C). If the reading does not max out, suspect a problem in the ground circuit or voltage supply to the sensor.

5. Voltage and Ground Circuit Checks: With the sensor disconnected and using a multimeter, verify for a 5-volt reference voltage at one terminal of the sensor connector (relative to ground). Also, check for proper ground at the other terminal. If either the 5V reference or ground is missing at the connector, trace these circuits back to the PCM connector.

6. PCM Connector Checks and Circuit Repair: If 5V reference and ground are present at the PCM connector pins for the ECT sensor #2 circuit, but not at the sensor connector, there is likely an open circuit or short circuit in the wiring between the PCM and the sensor. Repair the wiring as needed.

7. PCM Replacement (Last Resort): If 5V reference and ground are absent even at the PCM connector pins, carefully remove the corresponding wire from the PCM connector and re-check for voltage at the PCM pin itself. If voltage is now present at the PCM pin after wire removal, suspect a short circuit in the wiring harness. If voltage remains absent even at the PCM pin, PCM replacement might be necessary, but this is a rare scenario and should be considered as a last resort after exhausting all other possibilities.

Important Note: While P2185 often points to a faulty temperature sensor, always thoroughly investigate wiring and circuit issues before assuming sensor failure. If you are not comfortable diagnosing PCM-related issues, it is advisable to seek assistance from a qualified automotive technician.

Related OBD-II Trouble Codes: P0115, P0116, P0117, P0118, P0119, P0125, P0128, P2182, P2183, P2184, P2186 all relate to ECT sensor circuit malfunctions.

For further assistance with a P2185 code, consult a repair manual specific to your vehicle or seek advice from certified mechanics. Remember, accurate diagnosis is crucial for effective car repair.

Disclaimer: This information is for informational purposes only and not intended as professional repair advice. We are not liable for any actions taken on your vehicle based on this information. Copyright protected.