Check of signals on socket ECM

ECM connector pins (from the wiring side)

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

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

Note. The waveforms displayed on the Nissan scan tool are shown above. Under each oscillogram, the scale division value is indicated.

DMMs are great for testing static electrical circuits and for capturing slow changes in monitored parameters. When conducting dynamic checks performed on a running engine, as well as in identifying the causes of periodic failures, an oscilloscope becomes an absolutely indispensable tool.

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

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

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

The reliability and ease of use of today's oscilloscopes do not require special knowledge and experience from the operator. Interpretation of the information obtained can be easily done by an elementary visual comparison of the oscillograms taken during the test with the following time dependences, typical for various sensors and actuators of automotive control systems.

Parameters of periodic signals

Arbitrary signal characteristics

Each signal taken with an oscilloscope can be described using the following basic parameters:

• amplitude - the difference between the maximum and minimum voltages (IN) signal within the period;
• period – signal cycle duration (ms);
• frequency - number of cycles per second (Hz);
• width is the duration of the rectangular pulse (ms, ms);
• duty cycle is the ratio of the repetition period to the width (In foreign terminology, the inverse duty cycle parameter is used called work cycle, expressed in %);
• waveform – a train of rectangular pulses, spiking, sine wave, sawtooth pulses, etc.

Usually, the characteristics of the failed device are very different from the reference, 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 – amplitude, frequency, signal shape and width of periodic pulses are analyzed.













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











The waveform produced by an oscilloscope depends on many different factors and can vary greatly.

In view of the foregoing, before proceeding with the replacement of the suspected component in the event that the shape of the captured diagnostic signal does not match the reference waveform, the result should be carefully analyzed.

Voltage

The zero level of the reference signal cannot be considered as an absolute reference value, – "zero" the real signal, depending on the specific parameters of the circuit under test, may be shifted relative to the reference (see range 1 in the illustration Digital signal) within a certain allowable 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 tested circuit 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 stabilization circuit (IAC), the signal voltage of which does not change in any way with a change in engine speed.

In AC circuits, the signal amplitude already unambiguously depends on the frequency of the signal source. So, the amplitude of the signal generated by the crankshaft position sensor (CKP) will increase with increasing engine speed.

In view of the foregoing, if the amplitude of the signal taken with the oscilloscope is excessively low or high (up to cutting off the upper levels), you just need to switch the operating range of the device by switching to the appropriate measurement scale.

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

Also, don't worry about waveform distortion such as skew at the bottom of the leading edge of the square wave (see illustration 5 for values Digital signal), unless, of course, the very fact of the flattening of the front is not a sign of a malfunction in the functioning of the tested component.

Frequency

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

The shape of the recorded signal can be edited and brought to a form convenient for analysis by switching the scale of the time base of the image 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 bring the signal to a readable form, it is enough to switch the time base scale of the oscilloscope.

In some cases, characteristic changes in the signal turn out to be reversed with respect to the reference dependences, which is explained by the reversibility of the connection polarity of the corresponding element and, in the absence of a prohibition on changing the connection polarity, can be ignored in the analysis.

Typical Signals of Engine Control Components

Modern oscilloscopes are usually equipped with two signal wires, coupled with a variety of probes that allow 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 must be connected to a properly grounded point (mass).

Injectors

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

The duration of stay of the injectors in the open state is determined by the duration of the electrical impulses generated by the ECM, applied to the input of the e / m valves. The duration of the pulses is usually within the range 1÷14 ms.

A typical oscillogram of the pulse that controls the operation of the injector is shown in the illustration Fuel injector. Often, a series of short pulsations can also be observed on the oscillogram, following immediately after the initiating negative rectangular pulse and maintaining the injector solenoid valve 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 with an oscilloscope by visually observing the change in the shape of the control signal with varying engine operating parameters. So, the duration of the pulses when turning the engine at idle 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 stay open. This dependence is especially well manifested when opening the throttle with short presses on the gas pedal.

Using a thin feeler gauge, connect the red oscilloscope lead to the ECM injector terminal. Second signal wire probe (black) ground the oscilloscope securely.

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

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

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 markedly, followed by stabilization at a level equal to, or slightly less than, the characteristic idle speed.

Rapid closing of the throttle should lead to a straightening of the oscillogram, confirming the fact of overlapping of the injectors (for systems with fuel cut-off).

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

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

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	1÷6
2000÷3000 rpm	1÷6
Full throttle	6÷ 35

Inductive sensors

1. Start the engine and compare the waveform 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 contains oscillograms typical for the most commonly used zirconium-type lambda probes in cars, which do not use a reference voltage of 0.5 V. Recently, titanium sensors have become increasingly popular, the operating signal range of which is 0 ÷ 5 V, and the voltage level is issued during the combustion of a lean mixture, low - enriched.

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 screen of the meter with the reference one shown in the illustration.

4. If the recorded signal is not wavelike, but is a linear relationship, then, depending on the voltage level, this indicates excessive over-depletion (0÷0.15 V), or reenrichment (0.6÷1 V) air-fuel mixture.

5. If there is a normal undulating signal at idle, try to sharply squeeze the gas pedal several times - the signal fluctuations should not go out of range 0÷1 V.

6. An increase in engine speed should be accompanied by an increase in signal amplitude, 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 running at idle.



3. A sequence of rectangular DC pulses should be displayed on the oscilloscope screen. Compare the received waveform with the reference waveform, paying close attention to matching parameters such as amplitude, frequency, and pulse shape.

4. With an increase in engine speed, 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 running at idle.



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

4. Uneven spikes can be caused by excessive secondary winding resistance, as well as a faulty coil I/O wire.