DTC 15

Fig. 043 Chart Code 15 Coolant Sensor Circuit (Signal Voltage High):

Fig. 044 - Wiring Diagram for Code 15 Coolant Sensor Circuit (Signal Voltage High). VIN 8:

CODE 15, COOLANT SENSOR (SIGNAL VOLTAGE HIGH)

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (Thermistor) resistance is high, therefore the ECM will set a a high signal voltage. As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature, the voltage will measure about 1 to 1.5 volts at the ECM terminal 4.
Coolant temperature is one of the inputs used to control:
a. Fuel delivery.
b. Engine Timing (EST)
c. Knock Control (ESC)
d. Idle (IAC)
e. Converter Clutch (TCC)
f. Canister Purge (CCP)
g. Air Management (A.I.R.)
h. EGR

Code 15 will set if:
a. Signal voltage indicates a coolant temperature less than -31°F (-35°C) for 4 seconds.
b. Time since engine start is more than 1 minute.
If the coolant CKT 410 opens with the ignition off, this ECM will set -40°C (-40°F) and deliver fuel for this temperature. If the actual temperature is above approx. 7°C (20°F) the engine will not start due to the rich mixture unless "Clear Flood" is used by fully depressing the accelerator.
1. If voltage is above 4 volts, ECM and wiring are OK.
If location of sensor makes it hard to check, disconnect black ECM connector and check resistance between connector terminals 4 and 11.