Powertrain Controls - ECM/PCM

DTC 15 Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temperature Indicated):

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to the Powertrain Control Module (PCM). When the engine is cold, the sensor resistance is high, therefore the PCM will see high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops.

DIAGNOSTIC TROUBLE CODE (DTC) 15 WILL SET WHEN
^ Engine coolant temperature less than -36°C (-33°F).
^ Engine running for at least 8 minutes.

ACTION TAKEN (PCM will default to)
The PCM will use 18°C (64°F) as measured engine coolant temp and increase idle speed.

DTC 15 WILL CLEAR WHEN
The fault condition(s) no longer exist.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test determines if DTC 15 is a hard failure or an intermittent condition.
2. This test will determine if CKT 410 is open or for a faulty PCM.

DIAGNOSTIC AIDS
Check harness routing for a potential short to ground. After engine is started, the ECT temperature should rise steady to about 85°C (185°F). The default value will flash intermittently on the data screen.
The "Temperature to Resistance Value" scaled at the right may be used to test the engine coolant sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.