Powertrain Controls - ECM/PCM

DTC 73 Chart:

CIRCUIT DESCRIPTION
The coolant sensor circuit uses two pull-up resistors for temperature sensing. When sensor resistance is high indicating low temperatures, the PCM uses a 3.65 k ohms resistor and a 348 ohm resistor in series. As temperature increases to 50°C, the sensor resistance will decrease to 973 ohm. This resistance corresponds to 0.97 volt at the PCM. At this point the PCM shifts to the single 348 ohm pull-up resistor to measure temperature above 50°C. The PCM monitors the voltage signal of the circuit and assumes that engine operation causes coolant temperatures to change at slow rates. This diagnostic test monitors the engine coolant temperature sensor voltage. If the PCM detects a large change in sensor output voltage in a 1 second period of time, DTC 73 will set.

DTC 73 WILL SET WHEN
- Engine coolant sensor voltage has changed 0.3 volt 11°C (52°F) or more in one second.
- Two seconds have passed since ignition switch has been turned to the run position.

ACTION TAKEN (PCM WILL DEFAULT TO)
DTC 73 does not illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).

DTC 73 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. Checking DTC 73 snapshot value is used to determine if an intermittent high resistance or an intermittent low resistance caused the DTC to set. An intermittent high resistance can be caused by an open in CKT 410 or CKT 808. An intermittent low resistance can be caused by a short to ground on CKT 410.