Oh boy, I'm at my wit's end with this vehicle. Mazda help needed please.

2018 CX-5. It had the cylinder deactivation 'deactivated' by dealer shortly after purchase with a software update. It is current on all its software....been to 3 dealers...

181k miles on said car. Religious oil change intervals (5k, Mobile 1 0-20), filters, etc.

In the last 15k miles, the vehicle has had fuel injectors removed and bench cleaned, walnut blasted those intake valves due to build up, new exhaust manifold due to the upstream cat being a 1-piece design, new NGK plugs, new NTK coils, new NTK MAF, new upstream O2 (air fuel mix sensor) and new brake switch. Prior work on this car include resealing the timing case cover (timing chain inspection good) due to oil leaks. Trans service at 75k, 150k - new filter and Mazda fluid. Coolant valve assy was replaced upon failure, then reimbursed by Mazda once it went to recall status. In-tank fuel pump is not (today) part of the current open recall. The failure mode for that is 'it works, or it doesn't and the engine won't start'. So far there, all good.

Car runs well when it does run. Idles fine, revs ok and generally does good, but when it doesn't....

When cold, after starting, usually at the ~40mph speed, the car may stumble/jerk. Some times you can let off the gas and reapply and ease your way past that ~40mph 'wall'. Sometimes, the car freaks out, dies or near-dies, and you coast to the side of the road. Funny, it's not all the time when starting from cold. Or hot either.

Both Mrs and I see/experience a flashing check engine light. Traction control is illuminated (off) and the gauge cluster shows "smart city braking is disabled". Here's the thing: turn off the car and then restart it. Everything goes away like it never happened. No check engine light, traction is on and brake system is fine. Most often, none of this result in any codes being recorded. Not always, but I have pulled the following codes before:

U0401-00: Invalid data received from ECM/PCM 'A'; no sub type information

U0316-09: Software incompatibility with vehicle dynamics control module; component failure

U0415-68: Invalid data received from ABS control module; event information

Today, I was also able to see a misfire code for cylinder 1 too - P0301-24. Never seen a '-24' on your standard misfire code.

The last 15k or so miles, the misfires (any random 1 or more of the 4 cylinders) drove a lot of parts cannon repairs. A local Mazda dealer wanted $500 to replace 4 plugs...no kidding. Thieves. Those misfires, and overall 181k mileage on the car ate the upstream cat, hence its replacement. Downstream cat works fine. Temperature delta across cat is fine, and downstream O2 sensor is responsive and 'flat' as expected. Both O2 sensors are fine and like I said, when the car idles/runs fine, all is ok.

A Mazda forum I found also tossed the brake switch under the bus because if the sensor tosses a bad position to the computers, the smart brake system goes nuts. Old switch replaced with new - problems still happen.

All 3 local Mazda dealers have no clue, or say they do. The last dealer on their report said "found no codes. Test drove and noted hesitation when accelerating". Me trying to explain to the service writer there's no codes because I deleted them else the car would not work to get there (I printed out everything I found with freeze frame data), and said their tech noted the hesitation upon acceleration (which is the precursor to sudden failure, for which they ignored me), is why I'm here. That did not stop that dealer from telling me I NEEDED ~$4k worth of their services, from fluid changes to tires. No thanks.

What is the code combination of U0401-68, U0316-09, U0415-68 pointing to? I'm not ready to burn the car down as I believe with this taken care of, it could easily get another ~75-100k, but I am on the edge of dumping it for something else.

If anyone would like the names of the 3 local dealer goofs in the Puget Sound area, I'd be happy to pass along their poor service history. Just ask.

Thank you in advance!

 

I'm wondering if it could be something as simple as a loose ground or battery terminal...

 

With several DTCs in that category the first thing you "MUST" do is a health (load test) of the battery and as Alex pointed out to confirm the battery terminal to cable and cable to ground and starter are clean and have good connections.

The Battery must be charged and hold at least min. 12.5 volt. Anything less and the test will not be accurate, or your battery is needing to be replaced.
There are many auto parts that offer free battery load testing.

While I realize that most don't really give the exact information when going to service department at a dealership, the first post info really say to me to STOP using that dealership ?

There are several quality independent service shops in your state and city that have current ASE certified mechanics and or diagnostic technicians. Maybe you should consider using one. At least pay the hour fee and get the information on exactly what's wrong and what it needs to correct the issue.

 

Yah I'd also be getting a second opinion myself from a private mechanic who works on Japanese vehicles.

 

Thanks Alexmed2002 and Callisto, I appreciate your feedback.

The battery is relatively new, and both static and load tested fine. A little green around the neg terminal on the battery, so that was cleaned up just to 'be sure', as well as the main connection to the body just above the fuse panel. I'll trace out the other locations tomorrow, again to 'be sure'.

Yeah, stealers. Took it to the place we bought it from. Connected to Mazda's MGSS, found nothing and gave me back the keys. To their credit, they did NOT change me. Mazda #2, said 'it's your plugs', and told my wife it would be $500 to replace all 4. She was about to agree before I ended that crime. The plugs were less than a month old NGK ruthenium. I don't think so. They wanted to charge me $299 for an evaluation, to which I said pound sand, as the car never left the parking lot. They finally agreed. So I go 75 miles out of my way to stealer #3. Went there over a week in advance to tell them the details, with print outs and freeze frame data. Booked the appointment. Arrived at my 8:30 appt at 8am. I'm old school; if you're not early, you're late. They knew I was waiting in the customer lounge. Fancy looking place too. After 5 hours, I came to the desk and said 'and?'.....oh, err, well, we were just about to page you.... (not really - shop ticket closed 1.5 hr earlier). Uhh, we found nothing (tech took all the provided info and threw it away. Hooked car to MGSS, found no codes, and noted the hesitation when he drove it. Total tech time was 40 minutes.)

I griped this is EXACTLY what the problem was...the eventual warning light/limp mode fail was next. Head service writer said he's only charge me 1/2 for the 'diagnostic'. He held my keys. I paid the 1/2. On the way out they presented me with just over $4k of recommended services for the car. I just stared at him until he blinked and turned away.

Sure enough, as soon as I was puling out of the parking lot, the light show limp happened. I turned around and went right back to the guy and said 'bring out this tech'. They declined and said I would have to re-book an appointment. So I spent about 20 minutes blocking the service entry door with my dead car while taking my sweet time to erase the codes with my scanner. Once cleared the car was 'fine' and I left. The story, pictures, receipts went to Mazda USA a couple weeks ago. Stealer #3 has tried calling me 3 times to 'fix the situation'. They, too, can go pound.

I have a good independent I can turn to, so that's no issue. As these U codes screams 'software problem/fix', dealers have those jewels, not independents. My independent guy says dealers do this work, not them.

I'm open to any other suggestions, other than go buy a Toyota.

 

Please try not to take this the wrong way....
No the battery is likely NOT relatively new. This is a misconception and a topic misunderstood by so many! DIY and mechanic alike!!!
That is the first thing you need to check whenever there is anything that is battery supplied voltage.

Most all DIY should NOT be diagnosing their own vehicle if it has OBDII or CANbus and predominately manufactured from at least 2014 to preset.
This REQUIRES to be trained and I don't mean trained in surfing the internet for solutions.
As for directly relating to all your issues and many like it I post this at least every other day on various forums.... ONLY USE a service shop that has a CERTIFIDE ( and current really is a plus) Mechanic (trained in diagnostic trouble shooting) or the best is an Automotive Certified Diagnostic Technician.

Buying a Toyota will get you the same answers about from a person that actually is in the service mechanical industry with the credentials I mentioned and also DIY attempting servicing multiple problems at one time on a OBDII and CANbus ECU system

As for the advice I tried to give and help you and many other members on my time and most of the time while at work......
Sometimes it good to search information about a member responding on any forum and not assume that they are just another DIY .

 

Well then, thank you for your time. I do appreciate your prior suggestion. As for the battery, it is fine. So are the connections. Unless you suspect my Autel MS906 and BT506 are suspect. Each ground traced out and each cable ohmed out just fine. My shop manual was helpful in tracing the ground connections.

Again, appreciate your time.

 

If I were getting all these issues on a vehicle with 181,000 miles, I'd cut my losses and get another vehicle.
There comes a point in any vehicles life when throwing more money at is simply not worth it.
Is getting maybe another 20,000 miles worth the money and aggravation .
I think not, but that is my opinion, because number one I don't like throwing money away and/or giving myself unwarranted stress and headaches.
And at those miles everything else is just about worn out or already is, which means more money.
And despite all your sand pounding, you've already thrown money away

Good luck in whatever decision you make

 

Appreciate your input. I’m going to stick with this CX-5. It’s the ‘youngster’ in the family. 06 Miata 211k, 13 C-Max 240k, 03 CRV 310k and my preferred ride - 03 Acura TL-S 544k (and 3 transmissions, but that’s Honda 5spd autos for you).
Tracing wires and signals the last day. I may be on to something. Will advise.

 

Using s a multimeter and measuring ohms is not a very good method of checking earth connections. A multimeter only has 9 volts and milliamps of current to measure resistance. A voltage drop is a valid test as it measures the circuit under actual operating conditions. You may have overlooked the problem by measuring ohms.