P2185 code on a Honda

Diagnose and fix a Honda P2185 code

A P2185 Engine Coolant Temperature (ECT) Sensor 2 Circuit High Voltage is a fairly common problem on Hondas and Honda has even published a Service News Article to address the P2185 code problem.

A Honda P2185 may also be accompanied by the following trouble codes:
P0111 IAT sensor circuit range/performance problem
P0128 cooling system malfunction
P2183 ECT sensor 2 circuit range/performance problem

If you’ve already replaced the ECT #2 and still have the code, here’s the recommended procedure from Honda.

Here’s how to diagnose the P2185 code problem

Corrosion or a loose fit in the 2-pin ECT

Engine coolant temperature sensor

sensor 2 connector is most likely the cause of the problem.

1) Disconnect the ECT connector and examine both halves of the connector. Look for corrosion and terminal looseness. If you find corrosion, replace the connector with a new pigtail from Honda.

If there’s no corrosion, here’s how to test the connection and ECT sensor

To perform a diagnostic, use a multimeter to check for a 5-volt reference voltage on the yellow/red wire. If you see the 5-volt reference voltage proceed with the rest of the test. If no, locate the open between the ECU and the connector.

Plug the connector into the ECT sensor and run the engine until it’s at operating temperature. The ECT is a thermister that reports a high voltage when the engine is cold and a low voltage when it’s at operating temperature. Backprobe the yellow/red wire and read the voltage. At operating temperature, it should read only 0.5-1.0 volts.

If you see the 5-volt reference voltage but still see a high voltage during the backprobe on a hot engine, check the black wire for ground. If you don’t see ground, check for an open between the ECU and the connector.

©, 2021 Rick Muscoplat