Powertrain Controls - ECM/PCM

DTC 15 Chart:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor, a sensor whose resistance varies with temperature. The ECT sensor signal is on CKT 410 and sensor ground on CKT 808. As the temperature increases, sensor resistance decreases. High coolant temperature will result in low signal voltage on CKT 410. DTC 15 sets because the coolant temperature cannot be less than -29°C when Intake Air Temperature (IAT) is greater than -23°C.

DTC 15 WILL SET WHEN
- DTCs 37 and 38 are not set.
- IAT sensor signal is -25°C (-9°F) or greater.
- ECT sensor signal is -29°C (-20°F) or less.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 15 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will use the IAT sensor values in place of the normal ECT sensor values for the first 4.25 minutes of engine operation and then a default value of 90°C (194°F) for the rest of engine operation.

DTC 15 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. With the ECT sensor or wiring open circuited, Tech 1 parameter "ENG COOLANT TEMP" will read -29°C or less.
2. Checking for an open in CKT 410 from PCM to sensor. If Tech 1 shows 135-151°C with the coolant temperature sensor wiring harness terminals jumpered together, then CKTs 410 and 808 are OK.
3. Checking for an open in the sensor ground CKT 808 from sensor pin "A" to the ground splice. If shorting pin "A" to ground causes Tech 1 to show 135-151°C, then there is an open in CKT 808.
4. Checking the PCM's ability to recognize low voltage on terminal "B5" ECT sensor input. If grounding terminal "B5" causes Tech 1 to show 135-151°C, then there is an open in CKT 410 from the PCM to the coolant temperature sensor.

DIAGNOSTIC AIDS
A Tech 1 displays engine coolant temperature in degrees. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens.
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.