E073

Code E73:

Coolant Sensor 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 3.65K ohm resistor and a 348 ohm resistor in series. As temperature increases to 50°C, the sensor resistance will decrease to 973 ohms. This resistance corresponds to 0.97 volts 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 the PCM detects a large change in sensor output voltage in a 1 second period of time, the code will set.

TEST CONDITIONS:

1. 2 seconds have passed since ignition switch has been turned to the ON position.
2. 2 seconds have passed since the PCM has shifted coolant temperature pull up resistors. This occurs when sensor resistance indicates 50°C.

FAILURE CONDITIONS:

1. Coolant temperature voltage has changed 0.3 volts in 1 second.

ACTION TAKEN:

1. Code E73 sets.
2. No "SERVICE ENGINE SOON" telltale.

NOTES ON FAULT TREE:

1. A DVM or high impedance analog voltmeter may be used to look for quick changes that are too fast to be displayed through PCM data P.0.4. To monitor with a voltmeter, jumper harness terminals A and B to sensor terminals A and B. Connect DVM positive lead to jumper B and negative to jumper A. J35161 should be used to make jumper connections. Temperature and coolant sensor voltage should match what the expected temperature should be (85°C to 110°C) at hot idle. If temperature reading is shifted, replace coolant sensor and retest. Codes cannot be set or duplicated while in diagnostic mode.

2. A scan tool or voltmeter, using jumpers as described above, can alternately be used to observe changes while working underhood.

3. Since coolant temperature cannot change rapidly, a sudden change witch occurs at idle as the engine is warming up or idling hot most likely indicates a faulty coolant sensor. A terminal that is not properly crimped or backed out of a connector may cause a change in the resistance of the circuit.

NOTE ON INTERMITTENTS:

Manipulate the coolant sensor connector, engine to dash connector, and PCM connector while observing PCM data P.0.4 (or scan tool display). If a failure is induced the data or meter will change from its current reading. When voltage increases and temperature parameter decreases an open circuit is indicated, or voltage decreases and temperature parameter increases from its current value a short to ground is indicated. If an intermittent cannot be found, substitute a known good sensor and retest.

Code snapshot data captures the coolant sensor value and other operation conditions at the time the code was set. While it provides only one frame of data, an unexpectedly low value of L.0.4 from the Code E073 snapshot may indicate an open circuit or excessive resistance, while a high value indicates a short.