Checking signals on the ECM connector (Nissan Micra K12)

ECM connector contacts (from the wiring side)

Below are the test conditions and the corresponding signals taken from the ECM connector terminals.

Contact	Device	Terms and Conditions	Signal
1	ECM Grounding	The engine runs at idle speed	Grounding the motor
2	Post-catalytic lambda probe heater	A warmed-up engine operates at a speed of no more than 3800 rpm	0÷1 V
		The engine is off (ignition on) or the engine is running at speeds above 3800 rpm	11÷14 V
3	Throttle actuator relay power supply	Ignition is on	11÷14 V
4 (5)	Throttle actuator in closed (open) position	Engine off, ignition on, gas pedal released, manual transmission in 1st gear (AT in "D" mode)	Throttle actuator signal in closed position (voltage 0÷14 V) Throttle actuator open position signal (voltage 0÷14 V)
13	CKP sensor	The engine is warmed up and running at idle speed	CKP sensor signal at idle (average voltage 3 V)
		The engine runs at 2000 rpm	CKP sensor signal at 2000 rpm (average voltage 3 V)
14	CKP sensor	The engine is warmed up and running at idle speed	CMP sensor signal on X/X (voltage 1÷4 V)
		The engine runs at 2000 rpm	CMP sensor signal at 2000 rpm (voltage 1÷4 V)
15	Knock sensor	The engine runs at idle speed	About 2.5 V
16	Post-catalytic lambda probe	The engine is warmed up and operates at a speed not exceeding 3600 rpm	0÷1 V
19	E/M valve for controlling the purge of the absorber	The engine runs at idle speed	Signal from the electromagnetic valve of the absorber purge control to idle (voltage 11÷14 V)
		The engine runs at 2000 rpm	Signal from the solenoid valve of the purge control of the absorber at 2000 rpm (average voltage 10 V)
22, 23, 41, 42	Injector No.3,1,4,2 respectively	The engine is warmed up and running at idle speed	Injector signal on idle (voltage 11÷14 V)
		The engine is warmed up and running at 2000 rpm	Injector signal at 2000 rpm (voltage 11÷14 V)
24	Pre-catalytic lambda probe heater	The engine is warmed up and operates at a speed not exceeding 3600 rpm	Pre-catalytic lambda probe heater signal at speeds not exceeding 3600 rpm (average voltage 7 V)
		The engine is warmed up and operates at speeds above 3600 rpm	11÷14 V
29 // 30	Grounding the CMP // CKP sensor	The engine runs at idle speed	About 0 V
34	IAT sensor	The engine is running	0÷4.8 V, depending on temperature
35	Pre-catalytic lambda probe	The engine is warmed up and running at 2000 rpm	0÷1 V (periodic change)
45	Power supply for sensors	Ignition is on	About 5V
46 // 47	Power supply for the refrigerant pressure sensor K/V // TPS sensor	Ignition is on	About 5V
49	TPS Sensor 1	Engine off, ignition on, gas pedal released/pressed, manual transmission in 1st gear (AT in "D" mode)	More than 0.36 V // less than 4.75 V
51	MAP sensor	The engine is warmed up and running at idle speed	About 1.5 V
		The engine is warmed up and running at 2000 rpm	About 1.2 V
54 // 56 // 57	Grounding the knock sensor // MAP // refrigerant pressure sensor K/V	The engine is warmed up and running at idle speed	About 0 V
60, 61, 79, 80	Ignition signal in cylinders No.3,1,4,2 respectively	The engine is warmed up and running at idle speed	Ignition signal to idle (voltage 0÷0.1 V)
		The engine is warmed up and running at 2000 rpm	Ignition signal at 2000 rpm (voltage 0÷0.2 V)
62	Solenoid valve for controlling the phases of the intake valves	The engine is warmed up and running at idle speed	Signal from the electromagnetic valve of the intake valve phase control at idle (voltage 11÷14 V)
		When the engine speed increases to 2000 rpm when warmed up	Signal from the solenoid valve of the intake valve phase control at 2000 rpm (voltage 11÷14 V)
66	Grounding TPS Sensors	The engine is warmed up and running at idle speed	About 0 V
68	TPS 2 sensor	Engine off, ignition on, gas pedal released/pressed, manual transmission in 1st gear (AT in "D" mode)	Less than 4.75 V // more than 0.36 V
69	Refrigerant pressure sensor	The engine is warm and running; A/C and heater fan are on	1÷4 V
72	ECT sensor	The engine is running	0÷4.8 V, depending on temperature
73 / 74 / 82 / 83	Grounding of ECT sensor/lambda probe/APP1/APP2 sensor	The engine is warmed up and running at idle speed	About 0 V
85	Diagnostic connector	Ignition on, scanner disconnected	11÷14 V
86	CAN bus	Ignition is on	1.0÷2.5 V
90 / 91	Power supply for APP1/APP2 sensor	Ignition is on	About 5V
92	TPS sensor output signal (models with AT)	Engine off, ignition on, AT in "D" mode, gas pedal released // pressed	About 0.5V // 4.2V
94	CAN bus	Ignition is on	2.5÷4.0 V
98	APP Sensor 2	Engine off, ignition on, gas pedal released // depressed	0.3÷0.6 V // 1.95÷2.4 V
101	D/W brake lights	Brake pedal released // depressed	0 V // 11÷14 V
102	PNP sensor	Ignition on, AT in position "P" or "N" (Manual transmission in neutral position)	About 0 V
		Ignition on, transmission in other positions	11 ÷14 V
103	Tachometer output signal (models with AT)	The engine is warmed up and running at idle speed	Tachometer output signal (models with AT) on idle (voltage 10÷11 V)
		The engine runs at 2000 rpm	Tachometer output signal (models with AT) at 2000 rpm (voltage 10÷11 V)
104	Throttle Relay	Ignition off // on	11÷14 V // 0÷1 V
106	APP Sensor 1	Engine off, ignition on, gas pedal released // depressed	0.6÷0.9 V // 3.9÷4.7 V
109	Ignition switch	Ignition off // on	0 V // 11÷14 V
111	ECM relay	Within // 5 sec after engine shutdown (ignition off)	0÷1 V // 11÷14 V
113	Fuel pump relay	Within // 1 s after ignition is turned on	0÷1 V // 11÷14 V
115, 116	ECM Grounding	The engine runs at idle speed	Grounding the motor
119, 120	ECM Power Supply	Ignition is on	11÷14 V
121	ECM Backup Power	Ignition is off	11÷14 V

Note: The waveforms displayed on the Nissan diagnostic tool are shown above. The scale division value is indicated below each waveform.

Digital multimeters are great for checking static electrical circuits and for recording slow changes in monitored parameters. When performing dynamic tests on a running engine and when identifying the causes of periodic failures, an oscilloscope becomes an absolutely indispensable tool.

Some oscilloscopes allow you to save oscillograms in a built-in memory module with subsequent printing of the results or copying them to a digital medium in stationary conditions.

The oscilloscope allows you to observe periodic signals and measure the characteristics of rectangular pulses, as well as slowly changing voltage levels. The oscilloscope can be used to:

• Detection of unstable failures;
• Checking the results of the corrections made;
• Monitoring lambda probe activity;
• Analysis of the signals generated by the lambda probe, the deviation of the parameters of which from the norm is an absolute indication of a malfunction of the control system as a whole; on the other hand, the correctness of the shape of the pulses generated by the lambda probe can serve as a reliable guarantee of the absence of malfunctions in the control system.

The reliability and ease of use of modern oscilloscopes do not require any special knowledge or experience from the operator. The interpretation of the information obtained can be easily done by means of an elementary visual comparison of the oscillograms taken during the test with the time dependencies given below, typical for various sensors and actuators of automobile control systems.

Parameters of periodic signals

Characteristics of an arbitrary signal

Each signal captured by an oscilloscope can be described using the following basic parameters:

• amplitude – the difference between the maximum and minimum voltages (V) of the signal within the period;
• period – signal cycle duration (ms);
• frequency – number of cycles per second (Hz);
• width – duration of rectangular pulse (ms, μs);
• duty cycle – the ratio of the repetition period to the width (In foreign terminology, the inverse of the duty cycle parameter is used, called working cycle, expressed in %);
• signal form – a sequence of rectangular pulses, single spikes, sine waves, sawtooth pulses, etc.

Typically, the characteristics of a faulty device differ significantly from the reference ones, which allows the operator to easily and quickly visually identify the failed component.

DC signals – only the signal voltage is analyzed.











AC signals – the amplitude, frequency and shape of the signal are analyzed.





Frequency modulated signals – the amplitude, frequency, signal shape and width of periodic pulses are analyzed.











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Pulse Width Modulated (PWM) signals – the amplitude, frequency, signal shape and duty cycle of periodic pulses are analyzed.













The shape of the signal produced by the oscilloscope depends on many different factors and can vary significantly.

In view of the above, before proceeding to replace the suspected component in the event of a discrepancy between the shape of the removed diagnostic signal and the reference oscillogram, the obtained result should be carefully analyzed.

Voltage

The zero level of the reference signal cannot be considered as an absolute reference value – the "zero" of the real signal, depending on the specific parameters of the circuit being tested, may be shifted relative to the reference (see range 1 in the illustration Digital signal) within a certain acceptable range (see range 2 in the illustration Digital signal and 1 in the illustration Analog signal).

The full amplitude of the signal depends on the supply voltage of the circuit being tested and can also vary relative to the reference value within certain limits (see range 2 in the illustration Digital signal and 2 in the illustration Analog signal).

In DC circuits, the signal amplitude is limited by the supply voltage. An example is the Idle Speed Control (IAC) circuit, whose signal voltage does not change with engine speed.

In alternating current circuits, the signal amplitude is already clearly dependent on the frequency of the signal source. Thus, the amplitude of the signal generated by the crankshaft position sensor (CKP) will increase with increasing engine speed.

In view of the above, if the amplitude of the signal recorded using the oscilloscope is excessively low or high (up to the cutting of the upper levels), it is enough to simply switch the operating range of the device by moving to the corresponding measurement scale.

When checking circuits with electromagnetic control (for example, idle speed control system) when the power is turned off, voltage surges may occur (see 4 in the illustration Digital signal), which can be safely ignored when analyzing the measurement results.

You should also not worry about the appearance of such oscillogram deformations as skewed lower part of the leading edge of rectangular pulses (see values 5 in the illustration Digital signal), unless, of course, the very fact of the front flattening is not a sign of a malfunction of the component being tested.

Frequency

The repetition rate of signal pulses depends on the operating frequency of the signal source.

The shape of the signal being recorded can be edited and brought to a form convenient for analysis by switching the image time base scale on the oscilloscope.

When observing signals in AC circuits, the time base of the oscilloscope depends on the frequency of the signal source (see range 3 in the illustration Analog signal), determined by engine speed.

As mentioned above, to make the signal more readable, it is enough to switch the time base scale of the oscilloscope.

In some cases, characteristic changes in the signal turn out to be mirror-imaged relative to the reference dependencies, which is explained by the reversibility of the polarity of the connection of the corresponding element and, in the absence of a prohibition on changing the polarity of the connection, can be ignored during analysis.

Typical signals of engine management system components

Modern oscilloscopes are usually equipped with two signal wires along with a set of various probes, allowing you to connect the device to almost any device.

The red wire is connected to the positive pole of the oscilloscope and is usually connected to the ECM terminal. The black wire should be connected to a securely grounded point (ground).

Injectors

The composition of the air-fuel mixture in modern automotive electronic fuel injection systems is controlled by timely adjustment of the opening duration of the electromagnetic valves of the injectors.

The duration of the injectors' open state is determined by the duration of the electrical pulses generated by the ECM and fed to the input of the solenoid valves. The pulse duration usually does not exceed the range 1÷14 ms.

A typical oscillogram of the pulse that controls the injector operation is shown in the illustration Fuel injector. Often, the oscillogram also shows a series of short pulsations that follow immediately after the initiating negative rectangular pulse and maintain the electromagnetic valve of the injector in the open state, as well as a sharp positive voltage surge that accompanies the moment the valve closes.

The correct functioning of the ECM can be easily checked using an oscilloscope by visually observing changes in the shape of the control signal when varying the operating parameters of the engine. Thus, the duration of pulses when turning the engine at idle speed should be slightly higher than when the unit is running at low speeds. An increase in engine speed should be accompanied by a corresponding increase in the time the injectors remain open. This dependence is especially evident when opening the throttle valve by short presses on the gas pedal.

Using a thin probe, connect the red lead of the oscilloscope to the ECM injector terminal. Ground the probe of the second signal lead (black) of the oscilloscope securely.

Analyze the shape of the signal read while the engine is cranking.

After starting the engine, check the shape of the control signal at idle speed.

By sharply pressing the gas pedal, raise the engine speed to 3000 rpm - the duration of the control pulses at the moment of acceleration should increase noticeably, with subsequent stabilization at a level equal to or slightly less than that typical of idle speed.

Rapid closing of the throttle valve should result in a straightening of the oscillogram, confirming the fact of overlapping of the injectors (for systems with fuel shut-off).

During a cold start, the engine requires some enrichment of the air-fuel mixture, which is ensured by an automatic increase in the duration of the injector opening. As it warms up, the duration of the control pulses on the oscillogram should continuously decrease, gradually approaching the value typical for idle speed.

In injection systems that do not use a cold start injector, additional control pulses are used during a cold start of the engine, which appear on the oscillogram as pulsations of variable length.

The table below shows a typical dependence of the duration of the control pulses for opening the injectors on the operating state of the engine.

Engine condition	Control pulse duration, ms
Idle speed	1÷6
2000÷3000 rpm.	1÷6
Full throttle	6÷ 35

Inductive sensors

1. Start the engine and compare the oscillogram taken from the output of the inductive sensor with the reference one shown in the illustration.

2. An increase in engine speed should be accompanied by an increase in the amplitude of the pulse signal generated by the sensor.

Lambda probe (oxygen sensor)

Note. This subsection provides oscillograms typical for the most commonly used zirconium-type lambda probes in cars, which do not use a 0.5 V reference voltage. Recently, titanium sensors have become increasingly popular, with an operating signal range of 0÷5 V, with a high voltage level being generated during lean-mixture combustion, and a low voltage level being generated during rich-mixture combustion.

1. Connect an oscilloscope between the lambda probe terminal on the ECM and ground.

2. Make sure the engine is warmed up to normal operating temperature.



3. Compare the oscillogram displayed on the meter screen with the reference one shown in the illustration.

4. If the signal being removed is not wave-like, but is a linear dependence, then, depending on the voltage level, this indicates excessive depletion (0÷0.15 V), or re-enrichment (0.6÷1 V) air-fuel mixture.

5. If a normal wave-like signal occurs at engine idle, try sharply pressing the gas pedal several times - the signal fluctuations should not go beyond the range 0÷1 V.

6. An increase in engine speed should be accompanied by an increase in the signal amplitude, and a decrease by a decrease.

Ignition signal at the output of the ignition module

1. Connect an oscilloscope between the ignition module terminal on the ECM and ground.

2. Warm up the engine to normal operating temperature and leave it idling.



3. The oscilloscope screen should display a sequence of rectangular DC pulses. Compare the shape of the received signal with the reference one, paying close attention to the coincidence of such parameters as amplitude, frequency and pulse shape.

4. As the engine speed increases, the signal frequency should increase in direct proportion.

Primary winding of the ignition coil

1. Connect an oscilloscope between the ignition coil terminal and ground.

2. Warm up the engine to normal operating temperature and leave it idling.



3. Compare the shape of the received signal with the reference one - positive voltage surges should have a constant amplitude.

4. Uneven surges may be caused by excessive resistance of the secondary winding, as well as a faulty H/V wire of the coil.