Diagnostic Aids

WARNING: This page is about a different car, the 1995 Mazda MX-6 and 1995 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

Enter this TEST only when steps in QUICK TEST have been successfully completed but engine still does not start, or if directed here from another test or chart.

This test is intended to diagnose the following EEC-IV ignition systems and circuits:

Powertrain Control Module (PCM).
Spark (PCM-controlled).
Wiring harness circuits (PIP, SPOUT, IGN GND and VPWR).

To prevent replacement of good components, be aware the following non-EEC related areas and components may be cause of problem:

Fuel quality and quantity.
Ignition (general system condition).
Engine mechanical components.
Starter and battery circuits.
Distributor.
Camshaft Position (CMP) sensor.
Ignition Control Module (ICM).
Ignition coil.

1) Check No-Start Condition Try to start engine. If engine does not start, go to next step. If engine starts, no-start condition is intermittent. Check and repair ignition system as necessary. See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS - 2.0L article.

2) Attempt To Crank Engine Try to crank engine. If engine does not crank, check vehicle starting and charging systems. If engine cranks, go to next step.

3) Check VREF Signal At TP Sensor Turn ignition off. Disconnect Throttle Position (TP) sensor. Turn ignition on. Measure voltage at TP sensor harness connector between VREF and SIG RTN. If voltage is 4-6 volts, reconnect TP sensor and go to next step. If voltage is not 4-6 volts, go to TEST C.

4) Check For Spark At Plugs Disconnect any spark plug wire. Connect spark tester between spark plug wire and ground. Crank engine and check for spark. If spark is present and consistent, connect spark plug wire and go to step 14). If spark does not exist, connect spark plug wire and go to step 25).

5) Check For Spark At Coil Remove coil secondary wire from distributor. Install spark tester. Check for spark while cranking engine. If spark exists, connect coil wire and service ignition secondary system. If no spark exists, connect coil wire and go to next step.

6) Check Ignition Circuit Ground Continuity Turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058), leaving PCM disconnected. Disconnect Ignition Control Module (ICM) and Camshaft Position (CMP) sensor. Measure resistance between test pin No. 16 at breakout box and IGN GND circuit at CMP sensor connector or ICM connector. If resistance is 5 ohms or more, repair open in IGN GND circuit. Remove breakout box, reconnect components and repeat QUICK TEST. If resistance is less than 5 ohms, go to next step.

7) Isolate SPOUT Circuit Fault Reconnect CMP sensor and ICM. Connect PCM to breakout box. Set breakout box timing switch to DIST position. Try to start vehicle. If vehicle starts, go to step 12). If vehicle does not start, go to next step.

8) Check SPOUT Signal Turn ignition off. Set breakout box timing switch to DIST position. Set DVOM on 20-volt scale. Turn ignition on. Measure voltage between test pin No. 36 at breakout box and negative battery terminal while cranking engine. If voltage is 3-6 volts, EEC-IV system is not at fault. Remove breakout box, reconnect components and diagnose ignition system. See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS - 2.0L article. If voltage is not 3-6 volts, go to next step.

9) Check SPOUT & PIP Circuits For Short To Power Turn ignition off. With breakout box installed, move timing switch to COMPUTED position. Disconnect PCM. Disconnect CMP sensor and ICM. Turn ignition on. Measure voltage between test pin No. 36 (SPOUT) and negative battery terminal. Also, measure voltage between test pin No. 56 (PIP) and negative battery terminal. If either reading is more than 10.5 volts, repair short to power. Remove breakout box, reconnect components and repeat QUICK TEST. If both readings are 10.5 volts or less, go to next step.

10) Check SPOUT & PIP Circuits For Short To Ground Turn ignition off. Measure resistance between test pin No. 36 (SPOUT) and test pins No. 16, 20, 40 and 60 for short to ground. Also, measure resistance between test pin No. 36 and test pin No. 56 for short to PIP. Also, measure resistance between test pin No. 56 (PIP) and test pins No. 16, 20, 40, 46 and 60. If all readings are 10,000 ohms or more, go to next step. If any reading is less than 10,000 ohms, repair short in wiring harness. Remove breakout box, reconnect components and repeat QUICK TEST. If engine still does not start, go to next step.

11) Isolate Shorts In PCM Turn ignition off. Disconnect CMP sensor and ICM. With breakout box installed and PCM connected, measure resistance between test pin No. 36 (SPOUT) and test pins No. 37, 40, 57 and 60. Measure resistance between test pin No. 56 (PIP) and test pins No. 37, 40, 57 and 60. If any reading is less than 500 ohms, replace PCM. Remove breakout box, reconnect components and repeat QUICK TEST. If all readings are 500 ohms or more, reconnect components and go to next step.

12) Check PIP Signal Turn ignition off. With breakout box installed and PCM connected, move timing switch to COMPUTED position. While cranking engine, measure voltage between test pin No. 56 (PIP) and test pins No. 40 and 60. If voltage is 3-7 volts, replace PCM. Remove breakout box, reconnect components and repeat QUICK TEST. If voltage is not 3-7 volts, go to next step.

13) Check PIP Circuit Continuity Turn ignition off. Disconnect PCM from breakout box. Disconnect CMP sensor and ICM. Measure resistance between test pin No. 56 and PIP circuit at ICM or CMP sensor connector. If resistance is 5 ohms or more, repair open PIP circuit. Remove breakout box, reconnect components and repeat QUICK TEST. If resistance is less than 5 ohms, remove breakout box, reconnect components and diagnose ignition system. See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS - 2.0L article.

14) Verify SPOUT Signal If spark was present in step 4), turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install breakout box, leaving PCM connected. Ensure breakout box timing switch is in COMPUTED position. Set DVOM on 20-volt scale. Measure voltage between test pin No. 36 and test pins No. 40 and 60 while cranking engine. If voltage is 3-6 volts, go to step 21). If voltage is not 3-6 volts, return to step 9).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 14) to step 21). No test procedures have been omitted.

CAUTION: Use safety precautions when working on fuel system. DO NOT allow smoking or open flame. If fuel starts leaking, immediately turn ignition off.

21) Fuel Pressure Check Connect pressure gauge to vehicle. Note initial pressure reading. Pressurize fuel system by turning ignition on for one second and observe pressure gauge. Turn ignition off and wait 10 seconds. Repeat sequence 5 times. If pressure increases, go to TEST S. If pressure does not increase, turn ignition off and repair fuel system as necessary. See FUEL SYSTEM in TESTS W/CODES - 2.0L M/T article.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 21) to step 25). No test procedures have been omitted.

25) VPWR Circuit Check Turn ignition off. Disconnect CMP sensor. Turn ignition on. Measure voltage between VPWR circuit at CMP sensor harness connector and negative battery terminal. If voltage is more than 10.5 volts, go to step 5). If voltage is 10.5 volts or less, go to next step.

26) VPWR Continuity Check Turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install breakout box, leaving PCM disconnected. Measure resistance between VPWR circuit at CMP sensor connector and test pin No. 37 or 57 at breakout box. If resistance is less than 5 ohms, go to TEST B. If resistance is 5 ohms or more, repair open in VPWR circuit. Remove breakout box, reconnect components and repeat QUICK TEST.