2010 Mazda6 2.5 no communication with scan tool and no start

Tayyab Technician North Carolina Posted   Latest  
Resolved
Driveability
2010 Mazda 6 GS 2.5L (A) 5-spd
No Crank / No Start

No start with no com. with scan tool. checked all powers and grounds to the PCM. MAF has 5v reference with key on. Dash lights up with all lights including security, cel, abs and bunch of others. 

Main engine relay is not engaging, I can apply voltage and can hear fuel pump kick on and throttle body engaging. What should I do next?

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Daniel Technician
California
Daniel
 

Check for communication with other modules. If no communication the can bus is down or you have a issue with the dlc. If yes what codes are stored in the modules? Loss of communication with pcm codes will indicate its a pcm related issue not vehicle side issue.

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Tayyab Technician
North Carolina
Tayyab
 

I can't connect with any modules. Can't read VIN or connect via global. There is power at the DLC

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Alan Owner/Technician
Mississippi
Alan
 

Sounds to me like you're not getting a ground output from the PCM that's what controls the main relay see if you get a ground signal from Switched power from ignition switch to main relay. It interns Powers up and energizes other critical fuses needed to crank and run. Best of luck

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Timothy Owner/Technician
Wisconsin
Timothy
 

Find out where the bus is down. Who can you comm with, aside from the PCM? Start there.

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Tayyab Technician
North Carolina
Tayyab
 

Can't communicate with anything.

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Chris Technical Support Specialist
New York
Chris
   

Have you checked terminating resistance on the can bus. This is a very basic networking inspection that can be performed at the obd2 connector. Disconnect the battery, always good to do a battery reset anyway, and check for resistance between pins 6 and 14 at the obd2 connector. Almost every can network in the automotive world should read just over 60 ohms. If it reads 120 one of the two…

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Helpful
Timothy Owner/Technician
Wisconsin
Timothy
 

Go to the DLC and check for activity at pins 14/6, should have approximately 2.5V on both of the pins. Check across the two pins, should have around .4V, this indicates something is happening. If the voltage is high, then the circuits are shorted to voltage, if the circuits are low, then shorted to ground.

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Tayyab Technician
North Carolina
Tayyab
 

I think I have a lead. With BCM plugged CAN Bus resistance is 28 ohms with all modules plugged in. If I unplug BCM, resistance jumps to 120 ohms. I suspect the BCM is bad. Is that enough evidence to call it? There is 2.5v on both pins. I can only communicate with Instrument cluster and lighting control module.

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Timothy Owner/Technician
Wisconsin
Timothy
 

You can jumper the CAN lines at the BCM, and see if the circuits come back up. That would be further confirmation that the BCM is your culprit. Since every module puts out its own messages on CAN, you should be able to communicate then.

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Tayyab Technician
North Carolina
Tayyab
 

If I jump CAN lines with the BCM unplugged, resistance drops to 0 ohms.

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Timothy Owner/Technician
Wisconsin
Timothy
 

Whoa! That's no good. The bus is shorted together. Time to start removing modules one at a time, and see if the bus lines change resistance.

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Tayyab Technician
North Carolina
Tayyab
 

Just for clarification, by jumping can lines together with a wire with bcm unplugged and I'm measuring resistance at the dlc. Meter reads 0. Remove jumper wire meter reads 120. Connect BCM, meter reads 30 ohms. I unplug PCM or any other module, meter reads 80 ohms. Wouldn't that indicate BCM is bad? It is a junkyard BCM. This car has been to several shops over the past two years. Nobody…

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Chris Technical Support Specialist
New York
Chris
 

I think the test to jumper the lines is to connect the CAN+ to CAN+ and CAN- to CAN-, not jump CAN+ to CAN-. The BCM is a bridge between two sides of the CAN network, there should be two SETS of can wires at the BCM.

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Timothy Owner/Technician
Wisconsin
Timothy
 

As Chris said, there are four wires at the BCM. You've got to jumper the + to +, and the - to-. You're essentially bypassing the BCM to see if it's causing the issue.

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Tayyab Technician
North Carolina
Tayyab
 

Update: Airbag module was bringing the entire network down. Thanks for the help!

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Tayyab Technician
North Carolina
Tayyab Resolution
 

Update to all: I appreciate the help from each and everyone of you. This has been a great learning experiencing for me. The SRS module was defective, killed the entire network. Replaced that and I could communicate with all modules.

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