2005 Mazda 6 S 3.0L no start security light on

Car question:

Not sure if I can fix this wife's car problem or not but after reading some of your ATS technique, I thought it might be worth a shot. Here is the problem: the engine wont start and while I am cranking, the security light is coming on but it's off after a few seconds. There is no code and both spark and injector signals are nowhere to find. How do I start?

ATS Adviser:

This problem is a bit tricky because of the security light. Good thing is, the light is not on all the time and it goes off. It means it is only coming on during cranking under load. After checking the power supply diagram for the ecm, try checking the black wire going to the ignition switch inside your steering column. When you turn your key on, you should have 12 volts in there and not lower than 10 volts.

Make sure your battery is fully charged. Next, try testing also the black yellow wire voltage. do all these measurements at KOEO. If any of this test shows lower than 10 volts with fully charged battery then there is a voltage drop drawing the power supply to the ecm causing the security light to come on during cranking. Note also that when the security light is turned on, it will shut down the fuel so it will prevent the ecm from starting the engine.

Now if you suspect that all the ignition power supply is good then the common fix is to trace the power and ground supplies to the ecm if they are good or not. This will include checking also if the ecm is producing the vref that runs your crank or cam sensor.

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