P015

Sensor Circuit:

DESCRIPTION:
The engine coolant sensor is a thermistor, a sensor whose resistance varies with temperature. The engine coolant sensor signal is on CKT 410 and sensor ground on CKT 1076. As the temperature of the sensor increases, resistance decreases. High coolant temperature will result in low signal voltage on CKT 410. Code P015 sets because the coolant temperature cannot be less than -38°C when IAT is greater than -20°C.

TEST CONDITIONS:
1. Codes P037 and P038 not set.

2. IAT sensor value -20°C or greater.

FAILURE CONDITIONS:
Coolant sensor value -38°C or less for 2 seconds.

ACTION TAKEN:
1. PCM turns 'ON' the 'SERVICE ENGINE SOON' MIL.

2. PCM uses IAT sensor values in place of the engine coolant temperature sensor for the first ten minutes of engine operation, then the value of 9°C is used.

NOTES ON FAULT TREE:
1. With the ECT sensor or wiring open circuited, PCM Data PD04 will read -38°C or less. If the parameter does not show this, then the ECT sensor and wiring are OK; refer to 'NOTES ON INTERMITTENTS'.

2. Checking for an open in CKT 410 from PCM to sensor. If PD04 shows 148-151°C with the ECT sensor wiring harness terminals jumpered together, then CKT 410 and 1076 are OK.

3. Checking for an open in the sensor ground CKT 1076 from sensor pin 'B' to the ground splice. If shorting pin 'B' to ground causes PD04 to show 148-151°C, then there is an open in CKT 1076.

4. Checking the PCM's ability to recognize low voltage on terminal '3E16'. If grounding terminal '3E16' causes PD04 to show 148-151°C, then there is an open in CKT 410 from the PCM to the ECT sensor.

5. Checking for faulty mating of the PCM connectors. Fault is most likely at the PCM connector. Before replacing PCM.

NOTES ON INTERMITTENTS:
Manipulate ECT sensor wiring, ECT sensor connector, and PCM connector while observing PCM Data PD04. If the engine coolant temperature jumps from a normal reading to -38°C or less, repair the intermittent open circuit on CKT 410 or 1076. Remove and reconnect both the ECT sensor and PCM connectors and retest before replacing any components. If wiring and connectors check out OK, substitute a known good ECT sensor and retest.