(Solved) 2018 Mazda CX-5: no crank, no start

RJMARRA wrote:

vallis wrote: - - If I understood the diagram correctly, the Start Stop Unit sends power to Pin A of the starter relay, and the PCM grounds Pin E. I checked both pins with the test light by attaching one end to the + and the other to Pin E, but it did not light up. So this must mean there is no ground at the Pin. I did it the other way around for Pin A, no power when I push the start button.

With the ignition on, I supplied ground to Pin E and power to A, respectively, and it only cranked (I used a test light for Pin E as a ground medium to avoid cooking the PCM in case something goes wrong).

Pin A is wired to the start/stop unit and pin E goes to a connector the goes to both the start stop and the PCM. It does not specify if which is power and which is ground, you will have to determine that with your test light. One will be power and one will be ground. If that isn't the case we just narrowed down your problem

I have to add, it cranked only, it didn't start. It sounded like ignition and fuel are off.

RJMARRA wrote:

vallis wrote: - - If I understood the diagram correctly, the Start Stop Unit sends power to Pin A of the starter relay, and the PCM grounds Pin E. I checked both pins with the test light by attaching one end to the + and the other to Pin E, but it did not light up. So this must mean there is no ground at the Pin. I did it the other way around for Pin A, no power when I push the start button.

With the ignition on, I supplied ground to Pin E and power to A, respectively, and it only cranked (I used a test light for Pin E as a ground medium to avoid cooking the PCM in case something goes wrong).

Pin A is wired to the start/stop unit and pin E goes to a connector the goes to both the start stop and the PCM. It does not specify if which is power and which is ground, you will have to determine that with your test light. One will be power and one will be ground. If that isn't the case we just narrowed down your problem

I was thinking, the push button must send power to Pin A, in which case PCM would ground E.
The link below shows how this exact relay works even if it is for the previous model. If you scroll down to Type E, last one, you will see that the voltage is applied to Pin A and ground to E.

www.mcx5.org/relay_inspection-1142.html

If this is true and the previous model is the same way you have an input problem. Make sure the TCM PCM and Start Stop unit are all "alive"

RJMARRA wrote: If this is true and the previous model is the same way you have an input problem. Make sure the TCM PCM and Start Stop unit are all "alive"

It does seem to be an input problem. I verified that the PCM communicates with all sensors when I checked VREFs; at least we know it's not completely dead. I will check for TCM as you mentioned. As for the Start Stop unit, since the button turns the accessories on, it is somewhat awake; not sure about sending ignition signal though.

Update:

I located the j/c C-04, unplugged it, plugged in back in, then noticed the "Keyless System Malfunction" went away and it started for a few seconds, then died. I did it for the second time, and it started and died. I tried more times but no success. I wonder if disconnecting the connector resets the keyless system or there is some issue with the wires. Wires look intact and don't feel loose, although I did not do a thorough inspection.

If this is a wiring issue, wouldn't it stay running a little longer? The 2 times that it ran, it stayed on for exactly the same amount of time before it died; I'm thinking this could be a keyless system issue.

I also noticed that after it started and stopped, the throttle body stopped buzzing. I think the reason it was buzzing before is that it was thinking that the engine is running and it was trying to feed it air.

I've attached a couple of pictures of the C-04 connected and disconnected. Everything looks brand new there.

Any thoughts on this mysterious behavior?

do exactly what you did but instead of trying to start it, see if you can communicate with the PCM, if it’s enough to start it then maybe it’s enough to pull codes

RJMARRA wrote: do exactly what you did but instead of trying to start it, see if you can communicate with the PCM, if it’s enough to start it then maybe it’s enough to pull codes

I did it several times but won't start or read codes. While I was pushing the start/stop button on and off, I noticed that the turn signals do not work when the ignition is "ON". This explains why the scanner won't communicate with the vehicle and why it did not start when I supplied the power and ground to the starter relay, because the ignition was not actually ON when it looked like it's ON.

I removed the Start/Stop button and tested it as shown here: www.mcx5.org/push_button_start_inspection-207.html . Everything tested Ok although there could be an internal issue with the unit, which I suspect.

I'm going to dig for info on ignition diagnosis, but if there was anything to share, I would appreciate it!

I took a step back to start diagnosing the ignition issue and noticed several things that are not working are associated with the ignition not being fully ON.
- The shifter is stuck in park
- No turn signals
- No door chime
- No OBD2 communication
etc.

Push button was tested per service manual. It's in a good working order. I suspected the issue would be related to the BCM. I pulled the wiring diagram and upon measuring voltage, the wire going from the Start Stop Unit (pink) to the BCM has no power when I push the start button. Please see attached diagram. I checked continuity/resistance of the wire, and found no open circuit. So this leaves me with the Start Stop Unit, described here: www.mcx5.org/start_stop_unit-1320.html , www.mcx5.org/start_stop_unit_removal_installation-1324.html .

I will be checking for voltage as shown in page 2 of the diagram. Is there anything you can think of that would cause the ignition to not be fully ON?

yes, where ever you found that diagram (assuming its accurate) verify all of those measurements!

RJMARRA wrote: yes, where ever you found that diagram (assuming its accurate) verify all of those measurements!

In the diagram that I attached, the pink wire goes from the BCM to the Start Stop unit, not the other way around. That wire should have power when the ignition is on, but it's dead. Please see attachment to this post. The power comes from the battery through Hazard fuse 25A, enters the BCM, then outputs to Start Stop unit at pin 2D. This matches the pink wire in previous diagram. So, the start and stop unit does not receive power and it's not the only thing as some other accessories aren't working. I don't know if this confirms that the BCM is bad but it appears to be the case.

Back to IG2, the previous diagram shows IG2 RLY, but I can't find it anywhere, only IG2 fuse. Is it built in the Start Stop unit? Would you happen to have the front BCM diagram? The one I have isn't as detailed.

Thank you!!

vallis wrote: In the diagram that I attached, the pink wire goes from the BCM to the Start Stop unit, not the other way around. That wire should have power when the ignition is on, but it's dead. Please see attachment to this post. The power comes from the battery through Hazard fuse 25A, enters the BCM, then outputs to Start Stop unit at pin 2D. This matches the pink wire in previous diagram. So, the start and stop unit does not receive power and it's not the only thing as some other accessories aren't working. I don't know if this confirms that the BCM is bad but it appears to be the case.

Back to IG2, the previous diagram shows IG2 RLY, but I can't find it anywhere, only IG2 fuse. Is it built in the Start Stop unit? Would you happen to have the front BCM diagram? The one I have isn't as detailed.

IG2 "Relay" is solid state inside the FBCM if that diagram you posted is accurate. It switches the feed from the Hazard fuse to the IG2 circuit. The pink wire is the control for it. Can't tell from the diagram which of the two modules applies control voltage to that wire or what that voltage should be. And without a scan tool you don't even know whether the vehicle is attempting to turn IG2 on.

You need to find a way to scan the vehicle to move forward with diagnosing this.

Matt T wrote:

vallis wrote: In the diagram that I attached, the pink wire goes from the BCM to the Start Stop unit, not the other way around. That wire should have power when the ignition is on, but it's dead. Please see attachment to this post. The power comes from the battery through Hazard fuse 25A, enters the BCM, then outputs to Start Stop unit at pin 2D. This matches the pink wire in previous diagram. So, the start and stop unit does not receive power and it's not the only thing as some other accessories aren't working. I don't know if this confirms that the BCM is bad but it appears to be the case.

Back to IG2, the previous diagram shows IG2 RLY, but I can't find it anywhere, only IG2 fuse. Is it built in the Start Stop unit? Would you happen to have the front BCM diagram? The one I have isn't as detailed.

IG2 "Relay" is solid state inside the FBCM if that diagram you posted is accurate. It switches the feed from the Hazard fuse to the IG2 circuit. The pink wire is the control for it. Can't tell from the diagram which of the two modules applies control voltage to that wire or what that voltage should be. And without a scan tool you don't even know whether the vehicle is attempting to turn IG2 on.

You need to find a way to scan the vehicle to move forward with diagnosing this.

I have been trying to scan it but no success.

I was looking at the CAN, link below, to see if there is any way to tell which module controls the voltage. If you scroll down to the HS-CAN communication table, in the row where it says 'Cranking start', the the Front BCM, PCM and Instrument Cluster modules receive signal from the Start and Stop Unit. Would this mean that the Start Stop Unit sends the signal via the pink wire?

www.mcx5.org/controller_area_network_can_system-1163.html

vallis wrote: I have been trying to scan it but no success.

Do you know anybody with a pro level scan tool? Or even a bluetooth dongle might work with an app that'll scan all modules and let you manually enter the VIN. I've connected to a Nissan with a dead PCM with my MX+.

vallis wrote: If you scroll down to the HS-CAN communication table, in the row where it says 'Cranking start', the the Front BCM, PCM and Instrument Cluster modules receive signal from the Start and Stop Unit. Would this mean that the Start Stop Unit sends the signal via the pink wire?

That's referring to a "Cranking Start" message which is transmitted over the HS-CAN by the Start/Stop module. Nothing to do with that pink wire.

Matt T wrote:

vallis wrote: I have been trying to scan it but no success.

Do you know anybody with a pro level scan tool? Or even a bluetooth dongle might work with an app that'll scan all modules and let you manually enter the VIN. I've connected to a Nissan with a dead PCM with my MX+.

vallis wrote: If you scroll down to the HS-CAN communication table, in the row where it says 'Cranking start', the the Front BCM, PCM and Instrument Cluster modules receive signal from the Start and Stop Unit. Would this mean that the Start Stop Unit sends the signal via the pink wire?

That's referring to a "Cranking Start" message which is transmitted over the HS-CAN by the Start/Stop module. Nothing to do with that pink wire.

I don't know anyone who has scan tools. I have Forscan with activated license that is supposed to work, but I will have to try a different scanner.
Is this the one that you have? www.amazon.com/OBDLink-Bluetooth-Profess...&s=automotive&sr=1-2

vallis wrote: Is this the one that you have?

Yeah that's it. I pulled a VIN from ebay and it ID'd it as a 2018 Mazda. Had to manually select CX-5 and the KF option from pull downs. Shows enhanced diag available which should cover all modules on both the HS and MS CAN networks. That'll be codes and PIDs only. Their software doesn't include bi-directional controls or service functions.

Couple things before you pull the trigger on one. First the enhanced OEM stuff is only available for free in the phone apps. Their windows program is OBD-II only, but I think you can maybe pay to get some OE stuff in it.

Second I ain't saying it will communicate with your vehicle with the PCM offline. Just that it might.

Matt T wrote:

vallis wrote: Is this the one that you have?

Yeah that's it. I pulled a VIN from ebay and it ID'd it as a 2018 Mazda. Had to manually select CX-5 and the KF option from pull downs. Shows enhanced diag available which should cover all modules on both the HS and MS CAN networks. That'll be codes and PIDs only. Their software doesn't include bi-directional controls or service functions.

Couple things before you pull the trigger on one. First the enhanced OEM stuff is only available for free in the phone apps. Their windows program is OBD-II only, but I think you can maybe pay to get some OE stuff in it.

Second I ain't saying it will communicate with your vehicle with the PCM offline. Just that it might.

I will look into that, thank you!

Back with an update. I started disconnecting the modules and noticed something unusual. In the video below, as soon as I unplug the TCM (built into the control valve body), many of the accessories returned to normal, including the dash board chime, turn signals, and climate fan. The buzzing you hear in the beginning of the video is the throttle body. The fan noise is the interior fan kicking in as soon as the TCM is unplugged. I set it to high so I can hear it. Same behavior with the Electric Parking Brake module. I did not unplug all modules (I plan to) but it's not the case with the PCM.

As I was unplugging and replugging both modules, at one point the interior fan was still on with the TCM plugged in, I trying cranking it and it and started up. this time it did not die, but there was no communication. I turned it off and on about 5 times and it continued to start right up. But, when I disconnected the battery, the issue came back.

@RJMARRA, I measured voltage at the TCM pins per the diagram you shared (re-attached) and I have constant power at A, Ground at B and power at C when ignition is on.

Could there be a short in the data lines?

It is possible to have a short in the data lines, you can ohm test them. You must disconnect both sides of the line so it is not connected to anything. Take an ohm meter to both ends of the same wire which should be easy if both sides are unplugged and the wire is isolated. then after you get that reading do the same test but connect to one end of the wire (both sides still unplugged) and the other side to ground. if you have a reading there is a short to ground. you want to see OL

RJMARRA wrote: You must disconnect both sides of the line so it is not connected to anything. Take an ohm meter to both ends of the same wire which should be easy if both sides are unplugged and the wire is isolated.

Can you elaborate on the ends of wire part? I understand that I should unplug the TCM, that's one end, but where is the other end? I checked the data lines and they are all spread out across other modules. Also, since there are 4 data lines, do I test them all?

To properly ohm test a wire it must be completely isolated. This means that it must be unplugged at both ends, or if there is a splice you must unplug anything that wire connects to.