CX5 2015 Diesel SkyActiv 2.2L, Automatic Transmission
I had my battery disconnected for a day and now it’s like the ECU etc have forgotten everything. Didn’t have any of it prior to disconnection, car was driving fine. At the moment it starts normally and idles normally despite the faults.

Anyone able to chime in? TIA

Faults
- DSC Malfunction light
- TPMS System Malfunction light
- Parking Brake System Malfunction light
- Check Engine Light
- SCBS System Malfunction (No light. Just amber text message on display)
- Car changes gears roughly when accelerating/decelerating
- When in Manual, the numbers aren’t showing after “M” when up/down shifting through the gears e.g. M1, M2… M5
- Drivers side window won’t automatically wind up (though I found a fix on YT for this and it worked)

Existing Diagnostic Codes (Unable to erase them)
- P0098 - IAT Sensor #2 High Input
- U0442 - ECM/PCM invalid data (Transmission Control Unit)
- U0401 - ECM invalid data (4WD/ABS Control Unit)

Current condition and things I’ve checked
- The battery - has 12V of charge… no obvious defects with it and it’s internal indicator is green. Haven’t checked to see if Alternator is charging it, yet. No obvious drain on battery as all lights internal/external, instrument cluster and electric windows all work normally and shine brightly.
- Driveability - currently it starts normally. Idles normally. Changes gears (P/R/D) normally. Acceleration/Deceleration is smooth. Gear changes up and down are rough. Parking Brake operates normally.

I have what this person has
https://www.mazdaforum.com/forum/maz...n-fault-55093/

 

The ECU could not have changed it noel perimeters unless you did the wrong battery disconnect procedure and reconnect procedure. But even then, it not likely. I would first before going further to *have the battery load tested. (must be at least 12.50 stable voltage for the teat) Then carefully check and or clean the battery terminals, then disconnect the ground cable and make sure the metal is bare and clean and lastly if accessible remove the cable from the starter to the battery and also make sure it is clean and bare and reconnect. *The state of voltage or the age of the battery does not in any way indicate its present state of health.

Then restart the engine. If the engine check light is still on double check all the 3 areas of the ECU and make a notation and then you could if you don't like seeing the engine check light clear the ECU. This will place all the active codes into a permanent file until at least 2-3 complete cycles have been done. If the engine runs normally drive and as soon as the check engine light is activated retrieve the most current DTC and make note.

 

Thanks Callisto! I found the cause and it wasn’t the battery… more on that, in a bit…
But all the same, I think I’m going to still follow your advice because the battery is 5+ years old. It might even be the one the car came with.
The battery icon hasn’t turned ghost blue on the infomedia screen Fuel Economy page for a while (but the engine and aircon icons do).

OK so I had some of the engine apart to do carbon cleaning of the intake manifold. It involves taking the Intake accessories, EGR and accessories off of the engine as well as the manifold.
Turns out the P0098 IAT Sensor #2 High Input was correct diagnosis of the root cause. I had it off during the cleaning, plugged it back in during re-assembly, then ‘half’ unplugged it again (not completely disconnected but not connected) to re-route the wiring correctly, and then forgot to re-seat the connector completely back in, again.

Picture attached of the guilty sensor. I’m surprised such a small thing can cause such huge car problems.
After reading the internet for similar problems - most people had replaced the Battery, a Switch or a Sensor to fix their problems.

 

Glad you solved it.. IAT,MAP MAS sensors along with the throttle body should be cleaned at least once a year after your warranty [period has expired on any vehicle. Only use specified cleaners for each part.

If you battery is 5 years old I can almost guarantee it was going bad a more ore less a year ago and would not pass a load test. However for your piece of mind and also do it ASAP before you cause issues.

 

3-5 years max on a battery and closer to 3 years is the norm on new vehicles.
The OEM in my 2020 failed at about 13 months I replaced it with a "real battery

 

Thanks Callisto and Lobstah.

I’ll get onto that battery ASAP and do the terminal cleaning and ground wire check at that time. Fortunately the climate and roads here in Auckland NZ isn’t too laborious on the car. We don’t have to worry about extreme temp changes like in other countries.

 

Compared to OEM, what's a "real battery " that you would recommend?

 

Not sure you are asking what I think you want???
Why would want to compare to OEM and there really is no empirical data and fact that could support a comparison because of real world variables of service, maintenance and overall usage.
Most of the information is from DIY and that is not really anywhere close to a reliable source.

Personally, and not suggesting that anyone get them, but they tend to work better for most all my applications and currently all my vehicles car/truck have them is ....
I use OPTIMA. My Mazda is well loaded with additional electronic that needs a very high-quality battery.

Basically, there is NO battery that will outperform or last on average longer if you stay with name brand and at least spend a little extra to get the next upgrade specification from the base line requirement.
Mazda does not manufacture their own batteries.

 

Agreed. I just replaced the OE battery in my 21 with a Weize AGM unit (https://www.weizeus.com/products/wei...o-dohc-152-cid). Price was right and it was an exact match to the OEM. I was not having issues yet, but figured at almost 4yrs why not go ahead and replace it as the price was so reasonable at the time ($135 shipped to my door). I can't say I have noticed any difference in the longevity of my batteries. In my BMW which had an AGM initially, I tried a standard battery once, no difference. They all last about 4-5 yrs in my experience.

 

Good info and battery recommendation.


I want to add that this (in highlighted yellow) is most commonly stated on forums as well any service shop you talk to. Because we are not in the NEW habit of checking the batteries condition at seasonal changes or most never do until there is a problem. Many batteries will staill start an engine and give no indication of it beginning to fail ....until that one time you go out to start or re-start your vehicle and it's a no start. The comment when you find out it's a bad battery is.. "it didn't give me any indication it was going bad"!