E015

TEST CONDITIONS
1. Codes EO37 and EO38 not set;
2. MAT sensor value equal to or greater than -5°C.

FAILURE CONDITIONS
Coolant sensor value less than or equal to -38°C (Sensor signal open circuit).

ACTION TAKEN
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Soon" message on Driver Information Center (DIC);
3. ECM disables AIR Management valves;
4. ECM uses MAT sensor values in place of the coolant temperature sensor.

DESCRIPTION
The coolant sensor is a thermistor, a sensor whose resistance varies with temperature. The coolant sensor is a "two wire" sensor with sensor signal on CKT 410 (pin B) to the ECM and sensor ground on CKT 476 (Pin A) to the ECM. As the temperature of the sensor increases, resistance decreases. As resistance decreases, the ECM sees less voltage drop across the sensor and interprets it as high coolant temperature. High coolant temperature will result in low signal voltage on CKT 410 and low coolant temperature results in high signal voltage on CKT 410. Code EO15 "Open Coolant Sensor" sets because the coolant temperature cannot be less than -38°C when MAT is greater than -5°C.

Notes on Fault Tree
1. With the coolant sensor or wiring open circuited, ECM Data ED04 will read -38°C or less. If the parameter does not show this, then the coolant sensor and wiring are OK; see "Note on Intermittents."
2. Checking for an open in CKT 410 from ECM to sensor. If ED04 shows 148-151°C with the coolant 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 "A" to the ground splice. If shorting Pin "A" to ground causes ED04 to show 148-151°C, then there is an open in CKT 1076.
4. Checking the ECM's ability to recognize low voltage on terminal F16 "Coolant sensor input." If grounding terminal F16 causes ED04 to show 148-151°C, then there is an open in CKT 410 from the ECM to the coolant sensor.
5. Checking for faulty mating of the ECM connectors. Fault is most likely at the ECM connector. Before replacing ECM, perform "ECM Replacement Check", Chart C-1. Chart C-1 Vehicle Will Not Enter Diagnostics

Notes on Intermittents
Manipulate Coolant sensor wiring, Coolant sensor connector, and ECM connector while observing observing ECM Data ED04. If the 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 Coolant and ECM connectors and retest before replacing any components. If wiring and connectors check out OK, substitute a known good coolant sensor and retest.