Advanced Diagnostics

DTC P0125 (86) Advanced Diagnostics

DTC P0125:

Engine Coolant Temperature (ECT) Sensor 1 Malfunction/Slow Response





General Description

The powertrain control module (PCM) supplies voltage to the engine coolant temperature (ECT) signal circuit (about 5 V) through a pull-up resistor. As the engine coolant cools, ECT sensor 1 resistance increases, and the PCM detects a high signal voltage. As the engine coolant warms, ECT sensor 1 resistance decreases, and the PCM detects a low signal voltage. If the ECT sensor 1 output voltage does not reach a specified temperature at which closed-loop control for stoichiometric air/fuel ratio starts within a set time, depending on the initial coolant temperature after starting the engine, the PCM detects a malfunction and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status





Enable Conditions





Malfunction Threshold

The engine running time before the engine coolant temperature reaches 10 °F (-12 °C), based on the initial engine coolant temperatures, is as follows:






Driving Pattern

1. Start the engine under Enable Conditions (see "Initial engine coolant temperature").
2. Let the engine idle for at least 20 minutes.

Diagnosis Details

Conditions for setting the DTC

When a malfunction is detected during the first drive cycle with the ECT and intake air temperature (IAT) at engine start-up within the specified temperature range, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle with the ECT and IAT at engine start-up within the specified temperature range, the MIL comes on and a Confirmed DTC and the freeze data are stored.

Conditions for clearing the DTC

The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the battery.