Engine Control Module: Testing and Inspection

The Mazda Engine Signal Monitor (#49 9200 162) is used to check ECU terminal voltages. This tool inspects individual terminal voltages as selected with the monitor switch. A high impedance volt/ohm meter can also be used to check these voltages. Aftermarket test units are available that will read ECU terminal voltages when connected with proper adapters. Conduct tests with engine at operating temperature unless instructed otherwise.

TESTING WITH SIGNAL MONITOR

1. Connect signal monitor between ECU and wiring harness.
2. Place cover sheet on signal monitor face (#49 G018 904, 64 pin side).

NOTE: Use adapter connector A to check voltages at terminals 1A through 1V and 3A through 3Z. Use connector B to check terminals 2A through 2P.

3. Turn selector and monitor switches to select desired terminal number and measure voltage.
4. If any terminal voltage is incorrect, check the input or output device and related wiring. Only replace an ECU if other possible causes of abnormal voltages are eliminated.

CAUTION: Never apply voltage to SST terminals A and B.

ECU TESTING PRECAUTIONS [1]

1. If factory test equipment is not available, use only digital volt/ohm meter with minimum 10Meg ohms internal impedance for testing ECU terminal voltages.
2. Never push circuit tester probes into connectors from ECU side.
3. Before replacing an ECU, check components, wiring harnesses and terminal contacts. If terminal voltage readings are incorrect, check for other possible causes (lower than normal or zero voltage may indicate a short to ground in wiring. Higher than normal voltage may indicate an open circuit in wiring between that terminal and the corresponding input/output device, or a poor connection within a harness connector.) Repair as needed and recheck voltage readings.

[1] For more complete information on special precautions regarding handling and testing of electronic components, see Vehicle Damage Warnings.

ECU PIN VOLTAGE CHART

PART 1

ECU Terminal Voltage Chart (Part 1):

PART 2

ECU Terminal Voltage Chart (Part 2):

PART 3

ECU Terminal Voltage Chart (Part 3):

PART 4

ECU Terminal Voltage Chart (Part 4):

DECHOKE CONTROL SYSTEM

Dechoke Control System Testing:

1. Check that coolant temperature is below 0°C (32°F).
2. If not, disconnect water thermosensor and connect a resistor of approximately 10K ohms across harness terminals.
3. Turn ignition switch to "START" and verify that injector operating sounds (clicking) are heard.
4. Depress accelerator pedal fully and turn ignition switch to "START." Check that there are now no injector operating sounds.
5. If not as specified, check wiring, connectors and individual components such as water thermosensor, throttle sensor and injectors.