Code U0401 and now a code of C1001
As a new owner of a used 2018 mazda, CX5, which ive had for very short time of 4-5 weeks, is now setting a code of U0401.And the snap on scanner also said anti brake ,PCM
I erased it once about 10 days ago and its back. Is there any known issues with this code that i could check ??.
Also today i got beep sounds coming from inside car for a few seconds and i saw the pass seat belt light that is above the heater controls was flashing red. But now its back to what seems normal but is has a number 2 next to the light with no one in passenger seat. So i checked for codes again and all i found then was code C1001. And i think this code is for forward camera .
Are any of these to related ? which i dont think they would be. Or any known issues or fix ?.
There is no check engine lite on at the dash and car seems to be running ok.
I erased it once about 10 days ago and its back. Is there any known issues with this code that i could check ??.
Also today i got beep sounds coming from inside car for a few seconds and i saw the pass seat belt light that is above the heater controls was flashing red. But now its back to what seems normal but is has a number 2 next to the light with no one in passenger seat. So i checked for codes again and all i found then was code C1001. And i think this code is for forward camera .
Are any of these to related ? which i dont think they would be. Or any known issues or fix ?.
There is no check engine lite on at the dash and car seems to be running ok.
Last edited by carls2018; Aug 1, 2025 at 07:54 PM.
When you clear the DTC all you are doing is turning off the dash check engine light.
You need to look further in the ECU..
The reason the Check engine light returned is because the cause was not corrected.
So starting over the first thing is to load test your battery. Then make sure there is good clean terminal , ground at source and starter connections.
please don’t tell me the age of the battery of you have not done this yet it is meaningless.
Then use your snap-on scanner (That’s an except tools I own a Solus. ) for all ares of the ECU. You will find more info than just current DTC. If you don’t know how then find an ASE service shop get a Diagnostic service and have them tell you the problem. It’s worth the cost. Make sure they have a current ASE master technician or Diagnostic technician to do the 1 hour Diagnostic evaluation.
I recommend not to randomly change any part unless you have verified them either as the problem or faulty.
Sorry I can’t teach what takes a few weeks to learn and answers you will get for the most part are going to be guessing.
You do have a few issues and some are not related to the other , which goes back to my first service attention that needs to be done.
You need to look further in the ECU..
The reason the Check engine light returned is because the cause was not corrected.
So starting over the first thing is to load test your battery. Then make sure there is good clean terminal , ground at source and starter connections.
please don’t tell me the age of the battery of you have not done this yet it is meaningless.
Then use your snap-on scanner (That’s an except tools I own a Solus. ) for all ares of the ECU. You will find more info than just current DTC. If you don’t know how then find an ASE service shop get a Diagnostic service and have them tell you the problem. It’s worth the cost. Make sure they have a current ASE master technician or Diagnostic technician to do the 1 hour Diagnostic evaluation.
I recommend not to randomly change any part unless you have verified them either as the problem or faulty.
Sorry I can’t teach what takes a few weeks to learn and answers you will get for the most part are going to be guessing.
You do have a few issues and some are not related to the other , which goes back to my first service attention that needs to be done.
When you clear the DTC all you are doing is turning off the dash check engine light.
You need to look further in the ECU..
The reason the Check engine light returned is because the cause was not corrected.
So starting over the first thing is to load test your battery. Then make sure there is good clean terminal , ground at source and starter connections.
please don’t tell me the age of the battery of you have not done this yet it is meaningless.
Then use your snap-on scanner (That’s an except tools I own a Solus. ) for all ares of the ECU. You will find more info than just current DTC. If you don’t know how then find an ASE service shop get a Diagnostic service and have them tell you the problem. It’s worth the cost. Make sure they have a current ASE master technician or Diagnostic technician to do the 1 hour Diagnostic evaluation.
I recommend not to randomly change any part unless you have verified them either as the problem or faulty.
Sorry I can’t teach what takes a few weeks to learn and answers you will get for the most part are going to be guessing.
You do have a few issues and some are not related to the other , which goes back to my first service attention that needs to be done.
You need to look further in the ECU..
The reason the Check engine light returned is because the cause was not corrected.
So starting over the first thing is to load test your battery. Then make sure there is good clean terminal , ground at source and starter connections.
please don’t tell me the age of the battery of you have not done this yet it is meaningless.
Then use your snap-on scanner (That’s an except tools I own a Solus. ) for all ares of the ECU. You will find more info than just current DTC. If you don’t know how then find an ASE service shop get a Diagnostic service and have them tell you the problem. It’s worth the cost. Make sure they have a current ASE master technician or Diagnostic technician to do the 1 hour Diagnostic evaluation.
I recommend not to randomly change any part unless you have verified them either as the problem or faulty.
Sorry I can’t teach what takes a few weeks to learn and answers you will get for the most part are going to be guessing.
You do have a few issues and some are not related to the other , which goes back to my first service attention that needs to be done.
I originally saw the code U0401 when i was diagnosing my air bag light ,, which that is fixed now. (loose wires) .
And yes i know that erasing a code isnt a FIX. Im a 45 year retired tech.
I was just reaching out to see if any of the codes were a known issue with this year and model , and if there was any known problem area to look at.
And the battery stuff i know all about that, as age or even if new means nothing and they have to be checked. And i use the good old type of load testers ,,, not those new junk hand held units.
I wont say what i think about ,,ASE master technicians
Last edited by carls2018; Aug 1, 2025 at 09:32 PM.
None of your conditions are common problems in numbers or within the model years.
congratulation on your retirement . Me sorta semi retired got bored but never let my certifications lapse. Although I declined the L2 certification last year.
And yes there are some “Techs” that feel they don’t need to stay current and tend to show that in their work. Thats why when I do recommend a shop a state find one that has a current certified mechanic or Dignostic technician employed.
Good luck on your problem seems you should know how to find the problem and no how to service it.
I just looked at your profile ….I should have recognized the user name from previous posts .
congratulation on your retirement . Me sorta semi retired got bored but never let my certifications lapse. Although I declined the L2 certification last year.
And yes there are some “Techs” that feel they don’t need to stay current and tend to show that in their work. Thats why when I do recommend a shop a state find one that has a current certified mechanic or Dignostic technician employed.
Good luck on your problem seems you should know how to find the problem and no how to service it.

I just looked at your profile ….I should have recognized the user name from previous posts .

Last edited by Callisto; Aug 1, 2025 at 11:18 PM.
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