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I am hoping someone can help me. I have a 2008 Mazda Atenza and have owned the vehicle for approximately. two years with no issues, it has been regularly serviced by a Mazda garage. It is a keyless entry version with push start ignition and there have been no modifications to the car since I have owned it.

Approximately six weeks ago some lights flashed up on my dashboard then went away and the radio turned on and off then returned to normal. Nothing else happened so I didn't think too much of it. A couple of weeks ago the car refused to turn off after driving a short distance, I had to wait about 30 seconds before the push start/stop button turned the vehicle off. When driving the other week the red key warning light and security indicator light came on and stayed on for the duration of my drive (approximately 50mins). When I turned the car off and started it again, the lights did not display.

Whilst driving the car to a garage to get new tyres put on, several lights displayed on the dash including DSC Off, Security Indicator Light, ABS, Key Warning Light, Brake Warning Light and TCS/DSC. The radio would not turn on and the display that gives the heat controls also would not display. When I arrived at the garage the car would not turn off, nor come out of park. Mazda technicians came out and disconnected the battery to use manual override to get the car to start, they thought it could be power related and the immobiliser may have activated. Their diagnostic machine came up with several faults and codes relating to power supply and keyless entry issues. They took it to their workshop, kept it overnight and swapped some relays around which they hoped had fixed the problem, however it did not and two days later lights displayed once again on the dash and the car refused to turn off for a couple of minutes. Mazda have had the car for a further three days now and are none the wiser as to what is causing the problem.

Has anyone got any suggestions? It is in fantastic condition, never been in an accident (since I have owned it) and has done around 141,000 kms.
 

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Have you changed your tires, wheels or have you done ANYTHING to your tires at all within the last 2 months?
If not that, have you messed with anything electrical-related, such as your stereo?
 

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No nothing at all to either the stereo or tyres, or anything else in that matter. The tyres got changed after Mazda thought they had fixed the problem but they had nothing done to them before it played up.
 

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That's a head scratcher for sure.

Has the car recently been driven through any sort of deep water, or any type of water that could have been deep enough to splash up into the engine compartment? Typically the skid plate/splash guard would deflect this type of water. Do you know if your skid plate is still on the car? Sometimes it will be removed for an oil change or other work and the shop will forget to put it back.

The functions you're having trouble with seem to be split between ECU, BCM, and other things. If the issue was just the immobilizer, I wouldn't expect it to affect the radio or the HVAC systems. If it were fewer systems, I'd say look for a bad ground.

With so many different things going wrong, either you have separate causes that are coincidentally timed, or maybe you have a centralized electrical issue around the battery/alternator? If the charging system (battery+alternator) isn't providing enough power, it can cause the car's computers (plural) to behave very strangely and unpredictably. Honestly, that's where I'd start looking - make sure the battery and alternator are both providing proper output.

I'd also test the electrical system generally to try to figure out if there's a device (ie the blower motor) that's drawing more current than it should. The fuses are in place to prevent the wiring from overheating (fire) when something draws too much current. But if there isn't quite enough current draw to blow the fuse, or the fuse is faulty - maybe the vehicle's overall electrical system is getting pulled down enough to affect the computers?
 

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Interesting indeed. Can you try this out (whenever it's safe to do so that is)?
You've stated that pushing the ignition button after driving the car for a few miles does not turn off the engine. Can you try to HOLD the ignition button for 3-5 seconds and see if that does shut your engine off (depending on the car, you can also push the ignition button repeatedly 3 times in succession I believe)? The car SHOULD shut off engine immediately in this manner, and you will be in ACC (accessory) mode, with all your electrical systems still on.
 

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Discussion Starter #6
Interesting indeed. Can you try this out (whenever it's safe to do so that is)?
You've stated that pushing the ignition button after driving the car for a few miles does not turn off the engine. Can you try to HOLD the ignition button for 3-5 seconds and see if that does shut your engine off (depending on the car, you can also push the ignition button repeatedly 3 times in succession I believe)? The car SHOULD shut off engine immediately in this manner, and you will be in ACC (accessory) mode, with all your electrical systems still on.
I tried that, both methods you suggested when it refused to turn off last time and had no joy sadly. I am thinking of taking it to an auto electrican to get checked over. Not sure if that will do much but running out of ideas

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Discussion Starter #7
That's a head scratcher for sure.

Has the car recently been driven through any sort of deep water, or any type of water that could have been deep enough to splash up into the engine compartment? Typically the skid plate/splash guard would deflect this type of water. Do you know if your skid plate is still on the car? Sometimes it will be removed for an oil change or other work and the shop will forget to put it back.

The functions you're having trouble with seem to be split between ECU, BCM, and other things. If the issue was just the immobilizer, I wouldn't expect it to affect the radio or the HVAC systems. If it were fewer systems, I'd say look for a bad ground.

With so many different things going wrong, either you have separate causes that are coincidentally timed, or maybe you have a centralized electrical issue around the battery/alternator? If the charging system (battery+alternator) isn't providing enough power, it can cause the car's computers (plural) to behave very strangely and unpredictably. Honestly, that's where I'd start looking - make sure the battery and alternator are both providing proper output.

I'd also test the electrical system generally to try to figure out if there's a device (ie the blower motor) that's drawing more current than it should. The fuses are in place to prevent the wiring from overheating (fire) when something draws too much current. But if there isn't quite enough current draw to blow the fuse, or the fuse is faulty - maybe the vehicle's overall electrical system is getting pulled down enough to affect the computers?
Thank you for your reply. It hasnt been exposed to any weather elements or driven through water like you asked. An auto electrican has been suggested as a potential next step, and then a different mazda garage to see if they have any ideas. I will ask for the alternator/battery to be tested although I am pretty sure the battery isnt that old but will have it checked regardless

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I would check the battery before spending anything at a repair shop.
I have seen two different cars with both recent batteries, one was oem, one was aftermarket going with similar failures, with various electronic bugs, dash lights staying on forever, or refusing to start because of defaults in ecu.

What happens is if battery goes to low voltage during startup or shutdown of different buses the ecu or others controllers stays in a intermitent state.
Battery may take a drop in voltage when exposed to a high heat as it may be the case in summer.

How i test it, engine running you should get at least 14VDC, if not on idle, its sure it should get to 14 when throttling around 2500rpm. If not, alternator has probably failed.
Shutdown the engine, you should read at leat 12vdc constantly. If a rapid drop occurs the battery is dead. Let it rest for say, the night, and measure again, it should still show 12vdc at least if not either battery is almost dead or something is drawing current on it.
 
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