Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMAZDA2005MX-5 MIATA L4-1.8L DOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONOSCILLOSCOPE PATTERNS AND WAVEFORMS
2005 Mazda MX-5 Miata L4-1.8L DOHC
Oscilloscope Patterns and Waveforms
2005 Mazda MX-5 Miata L4-1.8L DOHCSECTION Oscilloscope Patterns and Waveforms
Inspection Using An Oscilloscope (Reference)
Fuel injection control signal
- PCM terminal
- No.1:2A(+) <=> 3A(-)
- No.2:2D(+) <=> 3A(-)
- No.3:2G(+) <=> 3A(-)
- No.4:2J(+) <=> 3A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 20 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up.
IAC control signal
- PCM terminal: 2P(+) <=> 2Q(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 25 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up (no electrical load).
Purge control signal
- PCM terminal: 3C(+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 10 ms/DIV (X), DC range
- Vehicle condition:
- ECT: above 80 °C {176 °F}
- D range and 7.5 km/h {5 mph} or below.
IGT control signal
- PCM terminal:
- 3F(+) <=> 4A(-)
- 31(+) <=> 4A(-)
- Oscilloscope setting: 1.0 V/DIV (Y), 50 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up.
Generator field coil signal
- PCM terminal: 3M(+) <=> 4A(-)
- Oscilloscope setting: 0.5 V/DIV (Y), 2.5 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up (no electrical load).
Engine speed signal
- PCM terminal: 30(+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 20 ms/DIV (X), DC range
- Vehicle condition: Idling.
Vehicle speed signal
- PCM terminal: 3T(+) <=> 4A(-)
- Oscilloscope setting: 1.0 V/DIV (Y), 10 ms/DIV (X), DC range
- Vehicle condition: Driving 50 km/h [31 mph].
SGC signal
- PCM terminal: 3V (+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 20 ms/DIV (X), DC range
- Vehicle condition: Idling.
NE signal
- PCM terminal: 3Y(+) <=> 4A(-)
- Oscilloscope setting: 1.0 V/DIV (Y), 5.0 ms/DIV (X), DC range
- Vehicle condition: Idling
Oil control valve (OCV) signal
- PCM terminal: 4D(+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 0.5 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up (no electrical load).
HO2S (front) signal
- PCM terminal: 4W(+) <=> 4A(-)
- Oscilloscope setting: 0.2 V/DIV (Y), 2.0 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up.
Fuel injection control signal
- PCM terminal
- No.1:2A(+) <=> 3A(-)
- No.2:2D(+) <=> 3A(-)
- No.3:2G(+) <=> 3A(-)
- No.4:2J(+) <=> 3A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 20 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up.
IAC control signal
- PCM terminal: 2P(+) <=> 2Q(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 25 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up (no electrical load).
Purge control signal
- PCM terminal: 3C(+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 10 ms/DIV (X), DC range
- Vehicle condition:
- ECT: above 80 °C {176 °F}
- D range and 7.5 km/h {5 mph} or below.
IGT control signal
- PCM terminal:
- 3F(+) <=> 4A(-)
- 31(+) <=> 4A(-)
- Oscilloscope setting: 1.0 V/DIV (Y), 50 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up.
Generator field coil signal
- PCM terminal: 3M(+) <=> 4A(-)
- Oscilloscope setting: 0.5 V/DIV (Y), 2.5 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up (no electrical load).
Engine speed signal
- PCM terminal: 30(+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 20 ms/DIV (X), DC range
- Vehicle condition: Idling.
Vehicle speed signal
- PCM terminal: 3T(+) <=> 4A(-)
- Oscilloscope setting: 1.0 V/DIV (Y), 10 ms/DIV (X), DC range
- Vehicle condition: Driving 50 km/h [31 mph].
SGC signal
- PCM terminal: 3V (+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 20 ms/DIV (X), DC range
- Vehicle condition: Idling.
NE signal
- PCM terminal: 3Y(+) <=> 4A(-)
- Oscilloscope setting: 1.0 V/DIV (Y), 5.0 ms/DIV (X), DC range
- Vehicle condition: Idling
Oil control valve (OCV) signal
- PCM terminal: 4D(+) <=> 4A(-)
- Oscilloscope setting: 2.0 V/DIV (Y), 0.5 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up (no electrical load).
HO2S (front) signal
- PCM terminal: 4W(+) <=> 4A(-)
- Oscilloscope setting: 0.2 V/DIV (Y), 2.0 ms/DIV (X), DC range
- Vehicle condition: Idling after warm-up.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.