Isuzu 4JA1 Workshop Manual page 521

Crankshaft Position (CKP) Sensor
Legend
1. Crankshaft Position (CKP) Sensor
2. Flywheel
3. Slit
The crankshaft position (CKP) sensor is located on top
of the flywheel housing. There are 4 slits spaced 90°
on the flywheel circumference. The CKP sensor is a
magnetic coil type sensor , which generates an AC
signal voltage based on the crankshaft rotational speed.
The ECM monitors both the CKP sensor and injection
pump camshaft position (CMP) sensor signals to
ensure they correlate with each other.
The following waveform aids to diagnose when there is
an oscilloscope or equivalent.
Engine Coolant Temperature (ECT) Sensor
- Amplitudes of CKP sensor signal (CH1) increase
as engine speed increases.
- Each waveform cycle shorten as the engine
speed increases.
CH1
0V
CH2
0V
RTW06ESH000101
Terminal: 90 (CH1), 91 (CH2) (+) / GND (-)
Scale: 10V/div 2ms/div
Condition: Approximately 1000RPM
RTW66ESH001401
Legend
1. Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature (ECT) sensor is
installed to the thermostat housing. The ECT sensor is
a variable resistor. The ECT sensor measures the
temperature of the engine coolant. The engine control
module (ECM) supplies 5 volts to the ECT signal circuit
and a ground for the ECT low reference circuit. When
the ECT sensor is cold, the sensor resistance is high.
When the engine coolant temperature increases, the
sensor
resistance, the ECM detects a high voltage on the ECT
signal circuit. With lower sensor resistance, the ECM
detects a lower voltage on the ECT signal circuit.
Engine Control System (4JH1) 6E-267
resistance decreases.
RTW66ESH001501
With high sensor