With TBI

Fig. 064 Chart - Code 15 Coolant Sensor Circuit:

Fig. 065 - Wiring Diagram for Code 15 Coolant Sensor Circuit. VIN 0, VIN 2, VIN E, VIN R, VIN U:

CODE 15

COOLANT SENSOR CIRCUIT

(SIGNAL VOLTAGE HIGH)

1.8L "J" AND 2.5L "A & N" SERIES

FUEL INJECTION (TBI)

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 see 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.
Code 15 will set if:
a. Signal voltage indicates a coolant temperature less than -35°C (-24°F) for 4 seconds.
b. Time since engine start is more than 1 minute.

Coolant temperature is one of the inputs used to control:
a. Fuel delivery.
b. Engine Timing (EST)
c. Idle (IAC)
d. Convertor Clutch (TCC)
If the coolant CKT 410 opens with the ignition off, the ECM will see -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. Engine will start using "Clear Flood" (which is Wide Throttle). However, "SERVICE ENGINE SOON" light will not come on, and code will not be stored, until engine run for one minute.
1. If voltage is above 4 volts, the ECM and wiring are OK. If checking resistance at the coolant sensor is difficult because of sensor location, disconnect black ECM connector and check resistance between connector terminals 4 and 11.